SC LR4-UGC Blast Planning

LR4LEARNER RESOURCE 4

IN UNDERGROUND COAL MINES& REPORTINGBLAST PLANNING

2 | LR4 V1 2009 © Department of Education and Training | www.skillsonline.net.au

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nAme ORGAnIsATIOn Allan Shoesmith Centennial Coal Bill Brooks WorkCover NSW Bruce McGeachie Xstrata Coal Cherie Chen DET NSW Claire Cappe DET NSW Craig Parker Pybar David Barker WorkCover Graham Cowan NSW DPI Graham Hogg Downer EDI Lawrence Buswell Barrick Gold Leanne Parker Hanson Lorenzo Laguna Rio Tinto, Northparkes Mihai Leonte NSW DPI Michael Creese Newcrest, Cadia Valley Operations

develOPed BY: Graham Terrey Mine Resilience Australia

develOPeR TeAm: Danny Duke Duke Consulting 2nd Project Coordinator David Chapman TAFE NSW Dorothy Rao SkillsDMC Giselle Mawer Giselle Mawer & Associates Robin Bishop Robin Bishop & Associates 1st Project Coordinator

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Shotfiring Course | Learners Resource 4: Blast Planning & Reporting - In Underground Coal Mines LR4 | 3

ABOUT THIS PUBLICATION: MODULE 4 – BLAST PLANNINg & REPORTINgThis Module (this ‘manual’ or LEARNERS RESOURCE, with its associated WORKBOOK) is designed to lead you on from Modules 1, 2 and 3. It makes assumptions about your knowledge and skill in storing, handling and transporting explosives, charging shotholes, and firing shots. It assumes you have the knowledge and experience to establish, implement & maintain blast plans and reports, and to become a shotfirer. It is also designed to consolidate your progress along a career path to becoming a shotfirer.

Commence work involving explosives

Work through Module 1

“Supporting Shotfiring – Storing, handling &

transporting explosives”

Be assessed for your relevant competencies

Continue to store, handle and transport explosives safely & well

Be assessed for ‘prior learning’ with explosives storing, handling & transporting


“Charging Shotholes”Be assessed for your

relevant competencies

Continue to support the shot crew and charge shotholes properly

Be assessed for ‘prior learning’ with charging shotholes


“Firing Shots”Be assessed for your

relevant competencies

Continue to connect sequences of shotholes and fire shots safely & well

Be assessed for ‘prior learning’ with firing shots


“Blast Planning & Reporting”

Be assessed for your relevant competencies

Continue as a shotfirer who supervises blasting


HOW TO USE THIS ‘LEARNERS RESOURCE’ – gETTINg STARTEDIf you have followed through Modules 1, 2 and 3, you will be familiar with these steps. This page is to help those who have dropped into the course in Module 4.

Decide to take an active role in your training and future

The material in this RESOURCE and in the WORKBOOK has been developed with countless years of combined practical experience and we hope you will find it both useful and rewarding.

Look at the ‘Contents’ of this LEARNERS RESOURCE and its associated WORKBOOK

Look in your Workbook at the Competency Units being covered, and, in particular, the Evidence Guide with its list of skills that you will be required to demonstrate (Demonstrated Ability) and the background knowledge (Required Knowledge).

Plan your training with your trainer / supervisor / manager

Your trainer will help you decide what you need to learn and help you design your training program. Your trainer will discuss with you how you might progress with this Module and/or progress to other Modules.

Start your learning and, at the points indicated throughout this RESOURCE, go to the

WORKBOOK to complete your ‘Knowledge Questions’ and ‘Learning & Assessment Tasks’

Successful completion of Knowledge Questions and Learning & Assessment Tasks is a great opportunity to gather evidence towards your assessment.

At the end of each of these activities, ask your trainer for feedback – your trainer is there to help you, and to keep you heading in the right direction.

Record your progress and get ready for your competency assessment

Use the checklist in your WORKBOOK to keep a record of your completed work. Raise any uncertainty with your trainer.

We’d appreciate any feedback to help make this material even better for future trainees

Jot down anything you come across during your work that:

1. was particularly valuable, or

2. could be made better

and discuss it with your trainer, who will pass your comments back to us.


‘REqUIRED KNOWLEDgE’ COVERED This publication is for people who are able to store, handle & transport explosives, who can charge shotholes, and fire shots, and now want to consolidate those skills and knowledge into becoming a shotfirer, specifically to:

1. Design & survey blasts:a. Knowing where and how you’re going to blast;b. Designing & surveying a blast;c. Thinking about the basic factors involved in a blast design;d. Understanding what happens in a blast;e. Calculating the burden & spacing of shotholes.

Then, having designed a blast, to:

2. Calculating the quantities of explosives required:a. Designing a range of blasting applications;b. Selecting a suitable powder factor; and,c. Calculating the explosive usage.

And, by knowing how much explosives is being used:

3. Identify the ‘Maximum Instantaneous Charge’:a. Knowing any restrictions;b. Remembering public safety too;c. Thinking about the tightness of the shot and

environmental consequences;d. Adjusting your ‘rule of thumb’ for site experience;e. Identifying problems and possible solutions;f. Selecting a shothole pattern; and,g. Planning the blast delay.

4. Monitor environmental impacts:

a. Being aware of environmental disturbances;b. Identifying causes of disturbance; and,c. Improving community awareness.

5. Reduce blast impacts:

a. Controlling variables;b. Reducing flyrock risk;c. Reducing ‘noise’;d. Minimising ground vibration

6. Dispose of unwanted explosives:a. Collecting and removing them;b. Destroying explosives;c. Complying with legal obligations

7. Maintain documents & Report:

a. Taking a systematic approach;b. Maintaining various records; and, c. Reporting.


CONTENTS

HOw TO use THIs ‘leARneRs ResOuRCe’ – GeTTInG sTARTed 4

‘ReQuIRed knOwledGe’ COveRed – BlAsT PlAnnInG & RePORTInG 5

BlAsT PlAnnInG & RePORTInG 9

WELCOME TO MODULE 4 9

Topics covered in each of the modules 9

PREVIEW 11

01 desIGn & suRveY BlAsTs 13

1.1 KNOWING WHERE AND HOW YOU’RE GOING TO BLAST 13

1.2 DESIGNING & SURVEYING A BLAST 14

1.3 THINKING ABOUT THE BASIC FACTORS INVOLVED IN A BLAST DESIGN 15

1.4 UNDERSTANDING WHAT HAPPENS DURING A BLAST 15

1.4.1 Stage 1 – Shock waves create micro-cracks in the rock 15

1.4.2 Stage 2 – High pressure gases push the ground apart 16

1.5 CALCULATING THE BURDEN AND SPACING OF SHOTHOLES 16

1.6 MANAGING SPECIAL CONDITIONS 18

02 CAlCulATe THe QuAnTITIes OF eXPlOsIves ReQuIRed 20

2.1 SMOOTH-WALL (INCLUDING LINE-DRILLING, PERIMETER & PRE-SPLITTING) BLASTING 20

2.2 SINKING A SHAFT OR WELL 24

2.2.1 Excavating a shaft 25

LEARNING & ASSESSMENT TASK 4.1A CALCULATE HOLE SPACINGS AND POWDER FACTORS 26

LEARNING & ASSESSMENT TASK 4.1B - SECONDARY BLASTING PROCEDURE 26

2.3 SELECTING A SUITABLE POWDER FACTOR 27

2.4 CALCULATING EXPLOSIVE REQUIREMENTS 27

LEARNING & ASSESSMENT TASK 4.2 QUANTITIES OF EXPLOSIVE REQUIRED 34


03 IdenTIFY THe mAXImum InsTAnTAneOus CHARGe & delAYs 35

3.1 KNOWING WHETHER YOU ARE RESTRICTED IN THE AMOUNT OF EXPLOSIVE FIRED ON ONE DELAY 35

3.2 REMEMBERING PUBLIC SAFETY, TOO 36

3.3 THINKING ALSO ABOUT THE TIGHTNESS OF THE SHOT & THE ENVIRONMENTAL CONSEQUENCES 36

3.4 ADJUSTING YOUR RULE OF THUMB FOR SITE EXPERIENCE 36

3.5 IDENTIFYING EXPLOSIVE QUANTITY PROBLEMS & POSSIBLE SOLUTIONS 37

3.6 SELECTING THE SHOTHOLE PATTERN 37

3.7 PLANNING THE BLAST DELAY 38

3.7.1 Blasting using delays 38

LEARNING & ASSESSMENT TASK 4.3 - MIC & DELAYS 39

04 mOnITOR envIROnmenTAl ImPACTs 40

4.1 BEING AWARE OF ENVIRONMENTAL DISTURBANCES 40

4.2 IDENTIFYING CAUSES OF DISTURBANCE 41

4.2.1 Flyrock 41

4.2.2 Dust 42

4.2.3 ‘Noise’, or airblast overpressure 42

4.2.4 Ground vibrations 44

4.2.5 Concussion from underwater blasting 45

4.3 IMPROVING COMMUNITY AWARENESS 46

LEARNING & ASSESSMENT TASK 4.4 – ENVIRONMENTAL MONITORING 48

05 ReduCe BlAsT ImPACTs 49

5.1 CONTROLLING VARIABLES 49

5.2 REDUCING FLYROCK RISK 50

5.2.1 Using a flyrock prevention Checklist 50

5.2.2 Using blasting mats 50

5.3 REDUCING DUST 51

5.4 REDUCING ‘NOISE’, OR AIRBLAST OVERPRESSURE 51

5.5 MINIMISING GROUND VIBRATION 53

LEARNING & ASSESSMENT TASK 4.5 – BLAST IMPACT REDUCTION 53


06 dIsPOse OF deTeRIORATed, ABAndOned OR deFeCTIve eXPlOsIves 54

6.1 COLLECTING & REMOVING EXPLOSIVES 54

6.2 DESTROYING EXPLOSIVES AND DETONATORS 55

6.3 COMPLYING WITH LEGAL CONSIDERATIONS 56

LEARNING & ASSESSMENT TASK 4.6 DISPOSAL OF DETERIORATED EXPLOSIVES – SAFE OPERATING OR WORK PROCEDURES 56

07 mAInTAIn dOCumenTATIOn & RePORT 57

7.1 TAKING A SYSTEMATIC APPROACH TO THE MANAGEMENT OF EXPLOSIVES USAGE AND RISKS 57

7.2 BEING ACCOUNTABLE & RESPONSIBLE FOR RECORDS 58

7.3 GIVING COMMITMENT TO YOUR SAFETY POLICY 58

7.3.1 Blast Management Plan 60

7.4 KEEPING RISK MANAGEMENT RECORDS 60

7.5 DOCUMENTING PROCEDURES 60

7.6 TRAINING & RECORDS 61

7.7 SUPERVISING & MAINTAINING SHIFT RECORDS 61

7.8 MAINTAINING SITE SECURITY, INDUCTION & ACCESS 61

7.9 MAINTAINING EQUIPMENT AND FACILITIES 61

7.10 MONITORING SAFETY & HEALTH, PRODUCTION, ENVIRONMENT AND COMMUNITY RELATIONS PERFORMANCE 62

7.10.1 Using Diaries 62

7.10.2 Complying with, or Enforcing Rules and Standards 62

7.10.3 Managing Risks - Risk Reccords 62

LEARNING & ASSESSMENT TASK 4.7 - RECORD-KEEPING 69

GlOssARY OF TeRms 70

A1 APPendIX 1 - nITROGlYCeRIne desTROYeR 77

A2 APPendIX 2 - BlAsT mAnAGemenT PlAns 78


BLAST PLANNINg & REPORTINg

WELCOME TO MODULE 4Welcome to Module 4 of the Shotfiring Course, which has been structured as a series of four modules each with a Learner Resource and Learner Workbook. The four modules are:

1. Storing, Handling, and Transporting Explosives

2. Charging Blast Holes

3. Firing Shots

4. Blast Planning & Reporting

This structure allows flexibility in the delivery of the training to accommodate differing roles, responsibilities and requirements of those who are involved in shotfiring.

TOPICs COveRed In eACH OF THe mOdules

MODULE 1

sTORInG, HAndlInG, & TRAnsPORTInG eXPlOsIves

1. Identify explosives & associated hazards and comply with Acts, Regulations, Standards and Codes by implementing risk management & procedures

2. Access & maintain storage and security of explosives

3. Transport explosives including defective explosives & emergency plans & response

MODULE 2

CHARGInG BlAsT HOles

1. Prepare for charging, including safety requirements and checking blast area and shotholes

2. Mix / manufacture explosives

3. Prime shotholes

4. Load explosives

5. Clean-up & Report


MODULE 3

FIRInG sHOTs

1. Hook up and test

2. Clear/isolate the area affected by the blast

3. Fire the shot

4. Conduct post-blast checks

5. Report

6. Return surplus explosives

7. Handle misfires

MODULE 4

BlAsT PlAnnInG & RePORTInG

1. Design / survey blasts

2. Calculate quantities of explosives required

3. Identify the Maximum Instantaneous Charge

4. Monitor environmental impacts

5. Reduce blast impacts

6. Dispose of explosives

7. Report

This publication is for people who are already familiar with storing, handling & transporting explosives, charging shotholes, and firing shots. Blast planning and reporting is a necessary part of being a shotfirer, who is accountable for conducting safe and efficient blasts and maintaining records, and specifically to:

1. Design / survey blasts:

a. Knowing where and how you’re going to blast;

b. Designing & surveying a blast;

c. Thinking about the basic factors involved in a blast design;

d. Understanding what happens during a blast;

e. Calculating the burden & spacing of shotholes;

f. Managing special conditions.

2. Calculate quantities of explosives required:

a. smooth-wall blasting;

b. testing against the real situation;

c. sinking a shaft or well;

d. calculating explosives requirements.

3. Identify the Maximum Instantaneous Charge & delays:

a. Knowing whether you are restricted in the amount of explosives fired on one delay;

b. Remembering public safety too;

c. Thinking about the tightness of the shot & environmental consequences;

d. Adjusting your rule of thumb for site experience

e. Identifying problems & possible solutions;

f. Selecting the shothole pattern;

g. Planning the blast delay.

4. Monitor environmental impacts:

a. Being aware of environmental disturbances;

b. Identifying causes of disturbance;

c. Improving community awareness.

5. Reduce blast impacts:

a. Controlling variables;

b. Reducing flyrock risk;

c. Reducing dust;

d. Reducing ‘noise’ or airblast overpressure;

e. Minimising ground vibration.

6. Dispose of explosives:

a. Collecting and removing explosives;

b. Destroying explosives and detonators;

c. Complying with legal obligations.


7. Maintain documentation & Report:

a. Taking a systematic approach to the management of explosives usage & risks;

b. Being accountable & responsible for records;

c. Giving commitment to your safety policy – including having a blast management plan;

d. Keeping risk management records;

e. Documenting procedures;

f. Training & records;

g. Supervising & maintaining shift records;

h. Maintaining site security, induction & access;

i. Maintaining equipment & facilities;

j. Monitoring safety & health, production, environment & community relations performance;

k. Complying with, or enforcing rules & standards.

PREVIEWWelcome to Module 4 in Shotfiring. The first Module covered storage, handling and transport of explosives, while Module 2 covered charging shotholes, and Module 3 discussed connecting and firing shots. These activities were performed as a member of a shot crew. In Module 1, you learned to treat explosives with respect. You learned that explosives contain large and powerful chemical energies, so it is vital to get their storage, handling and transport right the first time. They can be very unforgiving if mistreated but they are manufactured to deliver their energies in special ways in the robust environment of the mining, quarrying and civil construction industry.

In Module 2 you learned that once a shot is charged it is very hard, and can be very dangerous to make changes. There is little room for error, so the person who is responsible for the shot will want to be very certain that the whole team follows the charging procedure.

In Module 3 you learned that, following the charging of shotholes with explosives, you then connect the individual shots into a firing sequence. In doing this you must take care to avoid any cut-off risk, flyrock or misfire, so some basic checks are required. Every blast crew must follow a regular discipline in connecting primers from different holes. Each member of the blast crew must connect the

lines or leads the same way every time. Of course, you must also make sure no person or property is damaged. There are some key steps to take before the shot is fired and before anyone re-enters the area. Fragmentation is an important post-blast check but it is not the only check and a competent shotfirer will look at many things – from the throw of the blast to over-break and so on. Once the all-clear has been given, work may return to normal. Blasts must be recorded. These are essential for fine-tuning of explosives use, and charging and firing practices. They are also very useful in dealing with any complaint or legal challenge. Firing shots must be done carefully and in accordance with legal obligations.

Now, you are going to consolidate the knowledge and skills you’ve acquired – to improve your efficiency and effectiveness in using explosives – by helping you to fulfil blast management plan issues, including reporting in relation to blasting.

Preparation for blasting and thinking about blast survey and design requirements is the key to blasting efficiency and safety at work. Remember that explosives contain large amounts of energy that sometimes don’t give you a second chance. Always check the blast plan and the quality and accuracy of shotholes as one of the key steps in preparing to use explosives.

Also always calculate the amount of explosive to be loaded into each hole. Do this well before the charging and you’ll have the opportunity to refine your blasting or to take account of factors such as geology and perimeter (eg rib, roof) control that are easily forgotten to your regret. Think about the impact of the blast on the local community, too. Continually watch the amount of explosive in a shothole. The driller should have reported on any cavities in rock and any drilling irregularities. This helps refine a blast so that people not involved in the blasting can be protected. All blast design commences with ensuring protection against harm to people and property and meeting environmental restrictions.

Make sure everyone knows what to do and how to do it; they must be adequately trained in explosive-handling procedures and the blasting plan, so that everyone does the job the right way the first time. Explosives use is a team effort and everyone must do the same job the same way every time so anything out of the ordinary is easier to spot, and there are no frustrations. If a change is required the team should discuss the change and all agree that it’s best to make the change.


Be prepared for the worst so it doesn’t happen. Occasionally a misfire will happen so this was discussed in Module 3. Always check the blast for misfires before people are allowed to return to their work, but always check the blast for potential improvements and to refine the blast planning. Keep records to make these improvements. Blast planning and reporting must be done carefully and in accordance with legal obligations. Blast records are important in the event of a complaint, too.

These are some of the considerations you make when using explosives and this Module expands on these issues.

On completion of this Module you should be able to:

1. Estimate hole separation distances (the burden and spacing) for different blasts and work out how much explosive you will need for the shot and for each shothole. You will also be able to calculate the powder factor by knowing the burden and spacing.

2. Select the most appropriate powder factor, which is the amount of explosive you will need to break every cubic metre of rock under different situations. Alternatively you will be able to work back from a powder factor to work out the hole separation distances.

3. Restrict the amount of explosive going off on any one delay during the shot in order to comply with statutory limits or to improve the efficiency of your blast.

4. Monitor the environmental impacts from blasting to avoid undesirable disturbance for your neighbours or to help fine-tune your blasting method.

5. Control environmental impacts in different situations.

6. Dispose of unwanted explosives safely and legally with a view also to sharing information with other shotfirers/explosive users.

7. Maintain records and manage risks associated with explosive use.

Being able to demonstrate competency in the firing shots is necessary as part of the requirements to obtain a shotfirer’s licence. Other units of competency are also required for a shotfirer’s licence It is important that you check the requirements in your state/territory as requirements may differ for different types of shotfiring and in each state/territory.

AS2187.2 Use of Explosives

An explosive is any material or mixture of materials, which when initiated, undergoes a rapid chemical change with the development of heat and high pressure (see Australian Standard AS 2187.0 Use of Explosives, Glossary. AS2187 comprises three parts of particular interest to shotfirers; Part 0 is a glossary of terms or definitions, Part 1 deals with ‘Storage’, while Part 2 deals with actual usage or explosives practice).

The reaction proceeds very rapidly, and is self-sustained, as it follows and consumes its own available fuel. With the development of heat and high pressure, this reaction produces other more stable and largely gaseous substances.

AS2187.2 contains valuable information in addition to this Resource manual.

This resource deals only with commercially available explosives that have been approved by the Competent Regulatory Authority.


01DESIgN & SURVEY BLASTS

1.1 KNOWINg WHERE AND HOW YOU’RE gOINg TO BLASTA good system helps you to be organised so that it is easy to work with the changes that occur daily. Attendance at start-up meetings, pre-shift briefings or toolbox talks is vital to understand how your work will fit in with others and what sort of coordination is needed on the day. You will need to clarify where you are working and whether there are any others who might be affected by your work. The pre-work meetings provide an opportunity to sort out any difficulties before a problem arises.

You must know how much you’re blasting and check powder factors whether you’re working in an above–ground mine or working underground - both operations produce rock products for further treatment and sale. Explosives contain energy that works in two ways – sending out a shattering shock wave and exerting gas pressure to work on the shattering cracks and heave the ground apart. In the case of underground coal mining, the shattering shock wave is less influential in coal than it is in stone, but the heave is more effective in coal than in stone, but you should understand the difference. One day you might want to extend you underground experience to the surface. The construction of a road through rock is similar to mine or quarry blasts; in road cuttings you follow surveyed design lines and produce a certain volume of fragmented rock for filling, while cutting the excavation. Trenching is much the same, even if it is often of a smaller scale. Smooth–wall blasting is used to minimise ground disturbance, and enhance the long–term stability of the free rock faces, whether this is in a road cutting, for the final pit wall or in an underground crusher chamber. You probably won’t get a good feel for smooth-wall blasting while firing underground coal mine shots unless you do some ripping of the roof and you need to produce a smooth perimeter overhead for safety’s sake. You have to know where you’re going and what the result will be.

The thing that will change most is the direction of the throw of the rock in relation to shotholes. In typical quarrying shots and large stopes underground the rock throws perpendicular to the shotholes, while in a tunnel the rock commonly throws parallel to the drill hole. Trenching varies somewhere in between depending on trench dimensions, ground conditions and your drilling


design. In shooting coal underground you will mostly be shooting the coal at right angles to the shothole, while in shooting stone you will probably be shooting more like a standard tunnel where much of the rock travels somewhat parallel to the shotholes.

Important

All blast design commences with ensuring personal and public safety and meeting environmental restrictions, and ends in a factual analysis of the result so that you can make on-going improvements.

In all cases, a shotfirer must be able to produce the volume and fragmentation of rock required for the project. This will require a blasting plan, the scheduling of blasts, and the skills to prepare and confidently initiate the blast.

A plan of the blast site is essential and there are many ways to produce such a plan. In the case of underground roadways there will be a standard drawing so it will simply be a case of marking up the face and proceeding with drilling. For underground coal shooting a plan does not need to be complicated, but the hole layout needs to be fairly accurate with measurements of separation distances between holes and the face(s). A fairly simple plan drawing is far better than no drawing.

1.2 DESIgNINg & SURVEYINg A BLASTCommon steps in blasting are to:

1. Measure up the area to be blasted and establish the corners of the blast site and establish at least three reference points outside the blast area to know how far you are from cut-throughs or other structures / features.

2. Clean the area where you will be working and set it up properly.

3. Mark the boundary limits of the blast.

4. Design a blast using standard calculations using rules of thumb and/or mathematical formulae.

5. Decide which are the blast’s free faces and think about the geology and perimeter control required of the blast. This will help you decide on a suitable ratio or rule of thumb for your drillholes and their burden and spacing.

6. Select or check the powder factor suitable for the job, thinking twice about the hardness of stone, various stone bands, breaks in coal and water in holes.

7. Check the length and direction of the shotholes.

8. Drill all holes according to a design / pattern, ensuring they are of correct depth, inclination and location. Inaccurate drilling can reduce the actual burden and may cause a blow-out and flyrock.

9. Use a tamping stick, or other method to check the direction and inclination of each hole and move all drilling equipment away from the blast site.

10. Limit the charge or reduce the charge in each shothole according to the burden, or other key factor such as when smooth-wall blasting in stone is to incorporated.

11. Locate the primers at the bottom of each shothole based on a planned delay sequence. All explosives should be stacked on-the-job away from detonators and for preference in proper day storage boxes.

12. Fill each hole with explosive to stemming height, and in accordance with limits for the amount of explosive in each shothole.

13. Stem each shothole adequately. As a general rule, the stemming length should be greater than or equal to the burden and be at least 600mm in coal to keep the flame in the shothole.

14. Connect the initiation system.

15. Move everyone affected to a safe place and secure the area. Commence the usual warning sequence.

16. Conduct necessary tests and inspections and, if satisfactory, initiate the blast.

17. Return to the site after the dust and fumes have cleared. Check for misfires.

18. Give the “ALL CLEAR” signal.

Important

Good site planning and organisation are integral to safe blasting.


1.3 THINKINg ABOUT THE BASIC FACTORS INVOLVED IN A BLAST DESIgNTo design a blast it is important to understand the mechanisms of fracturing in-situ rock or other materials using explosives. As discussed in Module 1, when high explosives are properly detonated, they are rapidly and violently converted into gases at very high temperatures and pressures. We refer to this rapid conversion as detonation. The detonation creates both a shock wave and gas pressure, and you must think about how important a role each plays in a blast – it varies between coal and stone shots. Stone blasting takes advantage of both shock and gas pressure, while in coal you will have very little shattering effect or shock so you will be relying on gas pressure.

When a hole is charged and the energy is transmitted through rock, the rock will fragment according to the:

• strengthoftherock

• strengthoftheexplosive

• presenceofgeologicalfeaturessuch as joints, fault planes

• composition,extentandformationoftherock,and

• geometryoftheblast.

Basically, for any material to be broken, ruptured or penetrated, the explosive strength must be greater than the material strength. Geology plays an important role because, for example, shock waves won’t cross very well any joints that are pronounced in the rock mass.

1.4 UNDERSTANDINg WHAT HAPPENS DURINg A BLAST

1.4.1 sTAGe 1 – sHOCk wAves CReATe mICRO-CRACks In THe ROCk

Initially, the detonation of any high explosive sets up, almost instantaneously, shock (or stress) waves, which radiate from the drill-hole and into the surrounding rock as a compression wave. The extremely high pressure compresses the rock adjacent to the charge, and initiates radial cracks. These stress waves (compressive waves) move equally in all directions through the rock, provided the rock is intact; natural cracks in rock interfere with energy transmission. This is just like dropping a rock into a pond and watching the ripple spread out from there; the top of the ripple is the compression wave in action. The stress wave reduces in intensity with increasing distance, and with the condition of the ground, just like the ripple in the pond decreases in size the further out it goes. Rock is strong in compression (and much weaker in tension), so little rock disturbance occurs during that phase, except near the hole. The expanded gases remain confined in the shothole and radial cracks, provided the stemming has not been ejected.

To have the right sort of cracks develop there must be the right amount of explosive per cubic metre of rock. This is called the powder factor. For example, the powder factor for a quarry or open stope shot is typically 0.5kg of explosive for every cubic metre of rock, or 0.5kg/m3. This is where the rock moves at right angles to the shothole. In underground coal shots a typical powder factor is 2kg/m3, and this higher amount of explosive for every cubic metre of rock is due, in the case of stone, to the tightness of the shot – where the rock moves mostly parallel to the shothole even though you may have a drag round or reamed cut holes, which really only help the initial holes work to a free face at right angles to the shothole and give some room to expand. Very quickly this room is filled and there is nowhere for the rock to go except back along the tunnel – and parallel to the shotholes. In coal the powder factor has more to do with the lack of explosive efficiency caused by the softer nature of coal – meaning that you only have gas pressure to help you.


When the compression wave reaches a free rock face, it is usually reflected back as tension wave. This is just like the ripple bouncing back when it hits the edge of the pond. The bottom of the ripple wave in the pond is the tension zone, so the water or rock goes from compression to tension and back again in rapid succession. Since rock is much weaker in tension than it is in compression, the tensile shock wave fractures the rock material and cemented joints, leaving a trail of fractured material. The cracks are very fine, but play an important part in the ultimate result.

1.4.2 sTAGe 2 – HIGH PRessuRe GAses PusH THe GROund APART

The second stage of the explosion is a slower action; the explosive gases work much slower than the shock wave travels through the rock. Shock waves spread out very quickly. The fractures caused by the primary radial cracks, and the reflected tensile wave, destroy the strength of the rock between the hole and the free face. The compressed gases enter these cracks, and push the fragmented rock in the direction of the free face. If the shot has been properly designed, the gas pressure will cause the free rock in front of the drill-hole to yield, and move forward. In a proper design the explosives will be located at just the right distance from the free face, which is the easiest path for the gas to push the rock after it has been micro-fractured by the shock wave.

The tightness of the shot (as well as selecting suitable sequencing of shotholes) need to be considered when determining what powder factors are used. High and wide free faces will reduce a powder factor while narrower and deeper shots require higher powder factors.

The energy released when explosives detonate acts equally in all directions. However, fragmentation and rock movement occur through the paths of least resistance. In order to gain the maximum benefit from the detonation, shotholes should be charged and stemmed; gases are therefore confined, and forced to provide breakage, displacement and loosening of the surrounding rock. Stemming placed in the shothole with the explosive provides a gas-tight seal and improves performance, as discussed in Module 2, and in underground coal shotfiring there is an additional imperative in preventing gas or dust explosions.

The right design puts the explosive at the right distance from the free face to result in good fragmentation – the distance to the nearest free face is called the burden, while the distance that the holes are apart across the face is called the spacing.

Important

Every blast, other than pre-splitting, needs a free face or surface for the stress waves to reflect and fracture ground. In the case of pre-splitting, the shockwave emphasises the compression and consequently the tension that acts at right angles to crack the rock apart between the shotholes (Note that in pre-splitting, for the shockwave to work the holes must detonate at the same time to maximise the tension)

1.5 CALCULATINg THE BURDEN AND SPACINg OF SHOTHOLESThe following discussion aims to help you get a good feel for the differences in shooting stone and coal. It also assumes that might wish to extend your experience to tunnel work or surface shotfiring in the future. You will normally drill shotholes in coal at diameters of 38 – 40mm. This has increased over time from 28-32mm so the spacing of shotholes will have increased proportionally.

The drilling equipment that you already have on site will dictate to a large extent the burden and spacing of your shotholes. The bigger the shothole the further out the shockwave will have an impact because you have more explosive in each shothole. This helps you determine how far apart to spread the explosive throughout the rock. Larger diameter drill holes are generally cheaper to drill so the temptation is to drill larger diameter holes. However, these holes, which must be further apart for powder factor reasons, require longer stemming and can result in oversize rocks in the muckpile coming from the ground in between the shotholes, so there is limit to how far you can stretch the holes apart. The more consistent the rock is, and the more brittle the rock is, the more you can stretch the shotholes apart.


In a typical surface or quarry shot, open stope firing, road cutting or similar situation (where the rock is relatively strong and will travel at right angles to the shothole, and with gravity working for you by dropping the rock on the ground in front of the shot), shotholes holes will be about 30 times the hole diameter apart; this is a rule of thumb for your guidance, that you will refine with experience at a site. For example, shotholes of 89mm diameter will commonly be spaced 30 x 89 = roughly 2.7m apart (note: precision isn’t expected here because you’re dealing with a rule of thumb that depends on ground conditions and it would be unrealistic to expect precision about hole location). If the ground is riddled with imperfections such as jointing planes the shock wave will find it harder to travel and have an impact, but the gases might find it easier to work so the distance apart might go up or down with experience from the typical figure of 2.7m. The more brittle the rock the further apart will be the shotholes, but it would be rare to have a shothole more than 40 times the diameter apart. Columnar basalt will have to have holes a bit closer because the shockwave doesn’t cross the boundaries of the columns all that well. The geometry of the blast will also have an impact – the shorter the round compared to its width and height the easier it is for the rock to break loose, so the distance apart can increase. Rock that has strong walls – such as may be the case with some conglomerates – or that are close in will confine the rock and therefore need extra explosive so the holes will come in a bit closer.

In a tunnel underground the rock is held in tightly by the walls and will have to travel for the most part parallel to the shothole. Gravity is not working for you with the lower half of the shot so you will need to help by providing a bit more heave. In a typical tunnel the distance that the shotholes are apart is reduced to 20 times shothole diameter - because the explosive has to work harder. If a tunnel has holes of 45mm diameter then they will commonly be 45 x 20 = 900mm apart and for holes that are 50mm in diameter they will be 20 x 50 = 1m apart. This doesn’t apply to every hole of course; the holes

around the ‘cut’ will be up to half this distance apart due to the tightness of the shothole, consequently the need to turn the rock to fine particles and shoot it out so that other holes have somewhere into which they can expand – and to reduce the damage to the perimeter of the shot.

Trenches and other development will be somewhere in-between, depending on how tight the shot is going to be, and could, for example, be 25 times hole diameter for inclined holes and a wider trench, or 20 times hole diameter for a narrow/deep trench in rock. A drop-cut or box-cut to start a new road down into the next bench of quarry will be closer to a typical quarry shot in hole spacing but it will still be a tight shot, especially for the longer holes at the bottom of the drop cut. A wide sump will be like a fat trench, and so on.

A tunnel that is 5m wide by 5m high will have a hole spacing of around 20 times hole diameter for depth of round of 3.6 – 4m. However, if you were to try and pull a round of 5m deep you might need to close up the pattern (to around 17 times hole diameter) because the shot will be tighter.

A line of stripping holes along the walls of a tunnel will be different to the tunnel face, because the rock is not as tightly held in. Indeed, it will be more like a quarry shot because the rock is going to move at right angles to the holes. As a consequence you can spread out the holes to more like 30 times hole diameter. Some mines still use a hand-held drill for such stripping so the ratio of spacing to hole diameter can be useful.


Once you have the hole pattern, charts, such as Diagram 1 below, can help you work out how much weight of explosive will be charged into holes of different diameters for explosives of different densities, so you could calculate

the total weight of explosive used for a certain volume of rock. This – so many kilograms per cubic metre of rock - is called the powder factor, and different applications have different powder factors to guide you.

In coal, hole spacings are influenced by the nature of the coal itself and the consequent inefficiencies of the explosive in the softer rock, and are more likely to be of the order of 12.5 – 15 times hole diameter.

1.6 MANAgINg SPECIAL CONDITIONSFrom time to time difficult problems arise to give the blast designer something more to think about. One of these situations is hot and / or reactive ground. Remember that you shouldn’t use ordinary explosives and initiators in ground above 50 degrees Celcius. The ground you want to blast may be hotter than normal because it is:

• inanareaofgeothermalactivity

• agoodconductorofheatandishotonthe surface, particularly in an underground mine, despite the ventilation

• inornearburningcoalseams

• oxidisingsulphidemineralisation,especiallyifit very fine grained mineral such as pyrite.

Diagram 1: Charge weight chart (courtesy Orica, but another example can be obtained from Dyno Nobel)


Sometimes the ground is ‘reactive’. In this case, the chemical reaction involved is commonly of iron sulphides (pyrites in particular) being exposed to the air and water – resulting in ferrous ions and sulphuric acid. This particular chemical reaction produces heat. When you add nitrates to this, such as ammonium nitrate (the core ingredient in emulsion explosives with it’s excellent source of oxygen), the result is nitric oxide plus ferric ions and heat. The heat from this reaction supports increased oxidation and this causes the rock to heat up even more, until the heat build-up starts to run away. It has caused priming charges and plastics to melt, and explosives to burn and to detonate. Sometimes the ground is both hot and reactive.

It is always vital that you check the geology of the ground to be blasted, but it is even more important if you are in minerals that oxidise. This can happen in any rock – it can occur in a civil construction site, or in stone or coal seam in a coal mine - not just a metalliferous mine. It has happened surprisingly often in surface coal mines.

The hazards involved go beyond the chemical energy of the explosive itself, and include:

• hotsteamandgasesthatscaldaperson, as well as toxic vapours

• ignitionofvapourssuchashydrogensulphide (rotten egg gas)

• softeningandmeltingofplasticsusedinpriming charges and other initiators,

• meltinganddecompositionoftheexplosive products, and finally,

• detonationafterdecompositionofthe explosive products.

If you are going to blast in any rock it is wise to have someone with geotechnical skills to take a look at the mineralisation as well as any geological structures. You must be on the look-out for hot and / or reactive ground, and you must keep monitoring if you have the potential for reactive ground. With good information you can conduct a risk assessment and you may be able to identify zones of high, medium and low risk.

Once you have done the risk assessment you can write up some procedures and conduct training and education in how to treat the risks and respond appropriately. The sorts of things to cover can include:

1. marking out and defining zones of medium and high risk

2. constantly testing and monitoring the ground – maintaining a close watch on hole as well as surface temperatures in some cases – and this can go down to individual holes and zones within the shothole

3. minimising sleep times

4. potentially insulating or keeping the explosives away from the reactive ground – but be careful not to rely too heavily on shothole liners for this

5. charging shotholes from the initiation point so that you can quickly connect and fire if the temperature or other monitoring tells you that temperatures are rising to an unsafe level

6. other monitoring that might involve observers on the look-out for smoking or hazy ground

7. having a bigger buffer zone to expedite clearing the affected area in the event that you have to fire quickly

8. cleaning up any waste as soon as possible – spillage in surface shotfiring has been known to catch fire

9. choosing your initiation system carefully – you may not want extra delays

10. avoiding drill cuttings for stemming material, where these drill cuttings may be of the same reactive ground

11. gas monitoring in situations where toxic gases are being produced, with breathing apparatus at the ready in some cases, and

12. preparing to treat misfires. Time may be critical. It might make matters worse in some cases to wash out the explosive in the case of reactive ground while it may be preferable to do this in hot (but not reactive) ground. Observers may be vital during this operation – on the look-out for smoke and haze.

Reference

Additional reference material: An excellent Code exists for managing the risks of hot and / or reactive ground, and is produced by the Australian Explosives Industry & Safety Group (AEISG)


02CALCULATE THE qUANTITIES OF EXPLOSIVES REqUIRED

2.1 SMOOTH-WALL (INCLUDINg LINE-DRILLINg, PERIMETER & PRE-SPLITTINg) BLASTINgWall control is, like geological conditions, one of the most important factors to consider in blast designs in stone. Smooth-wall blasting is a method to help protect the stability of walls. Smooth-wall blasting is used to shape rock surfaces and produce smooth stable walls to minimise the need for secondary support and to ensure the long-term safety of the rock structure. Smooth-wall blasting is a pattern of closely-spaced shotholes that require no modification of the main blast, such as by pre-splitting. Perimeter blasting is a pattern of closely-spaced holes on the perimeter or final design line with a modified burden, and spacing for one or more rows in front of the perimeter holes. Perimeter-blasting underground would be very rare but the principle is important to understand because you may want to use it on the odd occasion. It is practised in underground metalliferous drives or tunnels.

Smooth wall blasting using post-splitting

Post-splitting is a perimeter-blasting method in which the bulk of the rock is removed in advance, such as might be the case in roadway headings – you would even contemplate perimeter-blasting in coal because you can’t take advantage of a shock wave in coal. Perimeter holes are charged at half the rate of the rest of the round and would not be tamped – you actually want the explosive to be de-coupled and to impart only a shock wave in the stone. Ideally they would be initiated on the same delay to maximise the collision of the shock wave between shotholes and the resulting optimum tension outwards from the line between shotholes. If they are not initiated on the same delay you are really only shooting more lightly than for the rest of the shot, so you would want to reduce the burden and spacing on each shothole.


2.2 TESTINg AgAINST THE REAL SITUATIONOnce you have a rough pattern you will often have to adjust the pattern to fit into the blast dimensions for the required opening. You will also have to allow for extra holes in the cut, and around the sides of the shot. You should take these into account when checking your powder factor.

Diagram 2a: Basic pattern for heading in stone

Types of cuts used in tunnelling and driving

Cut-holes can be a combination of charged of uncharged holes for developing free faces in rock to obtain the maximum advance per round. The type of cuts commonly used in tunnels are:

1. wedge cut

2. pyramid cut

3. drag cut

4. burn cut.

These cuts are generally placed in the centre of the drive to form the free faces necessary to fracture and displace the rock, as shown in Diagrams 2a to 2e. Every cut has an application so selection of the most suitable cut is important.

Angle cuts like wedge and pyramid cuts result in large pieces of rock being projected great distances along tunnels, risking damage to equipment. These cuts are most suited to smaller diameter and hand-held drills when reamed-out cut holes are not available. Wedge and pyramid cuts are not suited to long rounds that are more than about half the height of the tunnel because they are hard to drill. A pyramid cut is suitable for stone, but, like all angle cuts, results in projected rocks.

A drag cut can be placed at either side or at the top or bottom of the face, and is particularly useful in taking advantage of a potential slide, joint or head in the advancing face, or when blasting off a tunnel or drive that has important services in it, that you don’t want to damage. Because you are using the principle of firing to a free face - where the rock will move at right angles to the drill hole - you should get less rock projected in a way that causes damage.

A burn cut gives a relatively larger advance in small tunnels or drives. It is easier to set up, gives less scatter, and should only have water in the bottom lifter holes. It is not suitable for all types of rocks and it requires drill rigs that are (financially) not available to infrequent users. It increases the risk of gas or dust explosions by having a reduced burden and a greater chance of a blow-out to the reamed holes. A burn cut has a couple of extra (bulk) holes to help open up the cut.


Diagram 2b: Wedge cut in a tunnel blastDiagram 2c: Pyramid cut in a tunnel blast

Diagram 2d: Drag cut in a tunnel blast (holes not charged in roof represents smooth wall blasting)


Diagram 2e: Burn cut in a tunnel blast

Bulk holes and perimeter holes in tunnels or drives

Bulk holes are charged shotholes that fire to the hole created by the cut-holes, and which excavate the majority of the round as shown in Diagram 2a. Perimeter holes are charged and may contain some uncharged holes that form the final shape of the excavation, and may be increased in number with reduced burden and charge to protect the walls of the excavation; see Diagram 2d. In poor ground conditions, perimeter holes are charged with low strength, or cushion explosives, to minimise overbreak, so in underground coal mines in stone you might use less explosives and not tamp cartridges in perimeter holes – relying more on the shock wave and less on the heave of the high pressure gas that will work on the cracks created by explosives in good contact with the ground.

In civil works the tunnel shape will depend on the purpose. A typical tunnel used in a sewerage project in the Sydney area is detailed in Diagram 2f. In designing a tunnel blast, you could still set out the pattern on a ration of hole size to spacing. Alternatively you could refer to Diagram 2g and Diagram 2h respectively for

the recommended number of shotholes and explosives consumption for a given size of tunnel. Both diagrams apply to 45 mm diameter shotholes and 38 mm diameter explosives.

Diagram 2f: Sandstone tunnel blast plan

Diagram 2g: Determining the number of shotholes for a tunnel blast


Diagram 2h: Determining the explosive consumption for a tunnel blast

The burden and spacing of the charged and uncharged perimeter holes are commonly equal to, or less than, the burden and spacing of the bulk shotholes. Given that the calculated burden and spacing are only estimates, the appropriate burden and spacing can be determined by modifying these parameters with each consecutive blast until the desired result is achieved.

The powder factor in tunnels and drives is higher than for quarrying because you don’t have the free faces available in quarrying and gravity is not working with you for some of the holes. Typical powder factors in tunnels are around 2kg/m3, and this will go up to 2.3 for heavily jointed rock in which the shock wave cannot as readily cross joints, and down to 1.7 for massive or solid rock.

Remember that P1 and P3 explosives are normally used in shaft sinking or drift blasting, and can be fired singly, simultaneously or with a delay, where there is a risk of a gas or dust explosion. An example of a P1 explosive is Powergel Permitted 3000. To reduce the risk of flame igniting methane / dust mixtures, you will normally be restricted (by law, as is the case in NSW) to blasting no more than 800g (one 400mm long by 32mm diameter cartridge of Powergel Permitted 3000 has a weight of about 370g so you would normally be restricted to two cartridges) per shothole. You might be able to fire 1200g (three cartridges of 400mm x 32mm Powergel Permitted 3000) if your site has done a formal risk assessment and if the shotholes are up to 1800mm long, with a minimum burden between shotholes of 500mm and a minimum

length of stemming of 600mm. The total amount of P1 or P3 explosive to be fired in one shot is (in NSW) 1600g (approximately four cartridges of Powergel Permitted 3000 of 400mm by 32mm).

If you look at the following diagram of a roadway round in stone with a medium risk , for a roadway 4m wide by 3m high and 1.8m deep, giving a volume of = 4m x 3m x 1.8m = 21.6m3. There are 37 holes in the round. You would need to use Powergel Permitted 3000 of 370g per cartridge, with no more than 3 cartridges (= 1.1kg) in each hole so you would have = 37 x 1.1 = 41kg in the shot. The powder factor for this round = 41kg / 21.6m3 = 1.9kg/m3.

Diagram 2i: A drift round in a medium risk situation in stone

2.2 SINKINg A SHAFT OR WELLThe vital thing to understand with explosive use in shaft sinking is the reason for a high powder factor; typical powder factors range from 3 - 4kg/m3. Shaft-sinking is a procedure for excavating a steeply inclined to vertical opening from the surface of the earth to a desired depth for mining, ventilation, exploration purposes or for obtaining water. The shape of the shaft may be circular, rectangular or square in section - it will vary in dimensions depending upon its use, ground conditions, required depth, available capital and time.


Diagram 2j: Large-diameter circular shaft

The more drill holes on the perimeter of the shaft, the smoother the wall. For a larger-diameter circular shaft, the shothole pattern is generally arranged in concentric circular rings, with a central pyramid cut shown in Diagram 2j. In this excavation, the cut-holes form the new free in the rock, the bulkholes excavating the main volume of rock, and the perimeter holes defining the final shape. Information to calculate the number of holes required to blast a shaft for a given shaft area and powder factor is contained in Diagram 2k. The shaft design will depend on ground conditions and diameter. For example, if a 6 m diameter shaft is to be excavated, the estimated number of shotholes would be:

- in soft to medium strength rock 75 holes

- in medium strength rock 90 holes

- in hard, jointed rock 105 holes.

shaft diameter (m)

shaft area (m2) number of holes

3 7.0 30–50

4 12.5 40–65

5 19.6 60–80

6 28.3 75–105

7 38.5 100–115

8 50.3 130–170

9 63.6 150–205

10 78.5 180–250

Diagram 2k: Number of shotholes for shafts of various sizes

2.2.1 eXCAvATInG A sHAFT

1. Locate the shaft on a surface plan.

2. Mark the centre of the shaft, and securely establish four reference points away from the shaft for the purpose of locating the centre after each blasting.

3. Excavate the loose and unconsolidated material to competent rock, and stabilise the sides and surface platform.

4. Determine the shape of the shaft.

5. Determine the cut-hole pattern, and drill-hole pattern of the shaft and the total number of holes.

6. Prepare a chain or rope with links to locate the holes from a centre peg in the shaft.

7. Drill all holes to the required depth.

8. After drilling all holes, remove the drilling gear and blow out all holes with compressed air. Lightning strikes have been known to set off electric detonators in shaft-sinking operations more frequently than in other underground operations. All work should stop when lightning is in the area.

9. Prepare the primers. A major problem with shaft-sinking is water and the shorting of electric firing currents. Nonel, signal tube detonating systems can be a better alternative in low risk (of gas or dust explosion) situations.

10. If electric detonators are used, purchase a shaft harnesses with detonators already connected into a circuit, and positioned according to the blasting plan for easy placement into holes. Manufacturers supply the right length of detonators lead-wires, suitably connected and insulated. These harnesses


have heavier-gauge wire with heavy insulation in the ring-wires to prevent abrasion. The cost of the harness is offset by the improved results such as fewer misfires, better fragmentation and safety.

11. Place the primers in the bottom of each hole, and load the remainder of the hole with water-resistant explosive cartridges almost to the collar of each hole. Exercise full control over the exploder, or mains firing, and short-circuit box keys while explosives loading is in progress.

12. Join the electric detonator lead-wires in a series circuit with insulated joints.

13. Double check the blasting circuit.

14. Join the two single lead-wires of the blasting circuit to the firing cable as you move out of the shaft.

15. Leave any water in the bottom of the shaft to act as stemming and allay dust but make sure any connections are out of water.

16. Untwist, at the top of the shaft and in a safe place, the two wires of the firing cable and test the circuit.

17. If satisfactory, clear the area and initiate the shot. Initiate a shaft blast directly from a safe place.

18. After the blast, disconnect the exploder and join the wires of the firing cable.

19. Ventilate the shaft and only enter when the fumes have cleared. Do not to allow re-entry to the site until fumes generated by the explosions have cleared. Remember, fumes are toxic.

20. Before entering the shaft, disconnect electric detonator lead-wires from firing cable, short wires of firing cable and inspect blast.

21. Check for misfires.

22. Bar down any loose rock on the sides of the shaft.

23. Make the area safe before others enter the site.

LEARNINg & ASSESSMENT TASK 4.1A CALCULATE HOLE SPACINgS AND POWDER FACTORS

Assessment

Go to Assessment Task 4.1A in your Learners Workbook 4 “Blast Planning & Reporting”. Obtain a copy of two different blasting plans or standard designs used at your site. Find out what hole diameter(s) is drilled and the burden and spacing for shotholes; you may have two or more main sizes of drill holes – for example, one for development rounds and another for production blasts. Calculate the relationship between the burden and spacing and the diameter of the shothole(s). Compare your result with typical relationships for quarry/stope blasts or tunnel/drive headings. Comment on the difference or similarity and explain the difference or similarity.

LEARNINg & ASSESSMENT TASK 4.1B - SECONDARY BLASTINg PROCEDURE

Activity

Go to Learning & Assessment Task 4.1B in your Learners Workbook. Obtain a copy of the standard operating procedure for secondary blasting on your site, or describe the procedure used on your site.

If your site has chosen not to break rocks by secondary blasting, interview your supervisor or the person to whom they refer you, and write down or explain the reasons for this choice, and any circumstances that might cause them to reconsider their choice.

Cover all possibilities for secondary blasting including breaking up large boulders from main blasts, clearing large boulders from a crusher, and clearing large boulders as part of site clearing.


2.3 SELECTINg A SUITABLE POWDER FACTORIn the previous section we discussed a blast design that starts by calculating shothole spacings and check this against powder factors. You could just as easily have started blast designs by using rules of thumb for powder factors and checking your result against typical shothole spacing rules of thumb. Powder factor (sometimes in units of kilograms of explosive per tonne of rock, but please use the units of kilograms of explosive for every cubic metre of rock, or kg/m3) is the weight of explosive required to blast a unit of rock to the required size. The units commonly used are kilograms per (pre-blasted, in-situ or solid) cubic metre and grams per square metre for pre-splitting (g/m2). The following table sets out some suggested powder factors that you might use in blast designs.

Application Powder Factor

Quarry & large underground open stope blasting

0.5 kg/m3 of in-situ rock to be broken

submarine blasting 3-6 kg/m3 of in-situ rock using drill-holes to be broken

Trenching 0.5-1.5 kg/m3 of in-situ rock to be broken

Tunnelling 2kg/m3

shaft sinking 3-4 kg/m3 of in-situ rock to be broken

Plaster blasting 200g/m3 of free-standing rock

Plaster blasting 250-600g/m3 of embedded rock

Popping 100g/m3 of a free-standing using drill-holes rock

Popping 200g/m3 of embedded rock using drill-holes

Presplitting 250-400g/m2

Postsplitting 0.26kg/m3

Diagram 3: Typical powder factors

Example:

A tunnel blast of 21.6 cubic metres will typically require 21.6m3 x 2 kg / m3 = 43.2kg of explosive. This might be a face that is 4m wide by 3m high and drilling to a depth of 1.8m, resulting in a volume of rock 3m x 4m = 12 square metres by 1.8m deep = 12 x 1.8 = 21.6 cubic metres.

Knowing the amount of explosive required helps you get prepared for a shot. This is going to be more important for shots that change all the time, such as typical quarry shots or road cutting shots or open stope shots underground. However, if you were a shotfirer in an underground coal mine and the face you were about to charge was changed from your standard face you could easily tell the nipper how much explosive to collect by calculating it from the powder factor. You would need 2 kg for every cubic metre of face = 2 (25kg) cases in the example above.

2.4 CALCULATINg EXPLOSIVE REqUIREMENTSThere are three basic methods available for designing a blast:

1. a rough calculation method using the powder factor as the main parameter

2. an empirical method, which is based on the collection of data from research and productions blasts and presented as rules of thumb.

3. the use of computer programs to produce the optimum result in the design and calculation of blasting options.

All of these methods will only give an approximation of the solution. It will be necessary to refine your powder factor in consecutive blasts until the required (mainly fragmentation or wall control but possibly muckpile profile) results are achieved. The design of the perimeter holes should be considered.


In designing a blast that is close to the surface, first identify:

1. environmental constraints

2. airblast overpressure

3. ground vibration

4. flyrock

5. public safety

6. face height

7. selected powder factor

8. wet or dry holes

9. explosive type to be used and density

10. stemming depth selected

11. available hole diameters.

Also think that the rock will fragment according to the:

1. strength of the rock

2. strength of the explosive

3. presence of geological features such as joints, fault planes

4. composition, extent and formation of the rock, and

5. geometry of the blast

6. wall protection you want at the edges of the blast.

Case Study 1

Designing a low risk stone roadway blast

In designing a roadway blast as with most blasts, you might start with the ratio between the shothole diameter and the typical burden and spacing. For most blasts you already know what your drill hole diameter is going to be, because you already have a drill rig. We’ll do a couple of blast designs soon where you might start from another angle and calculate the drill hole diameter size required, but first try this way. In this example, you’ll be using a variation of a more common roadway design using permitted explosives, to illustrate how you might work out a design from first principles.

Step 1. Estimate the blast pattern

If the holes you use on site are 40mm diameter and it is a typical roadway shot then the ratio between hole diameter and hole separation is = 17 x hole diameter for emulsion use

= 17 x 40mm = 680mm or near enough to 700m for the burden (between rows) and spacing (between adjacent shotholes). The burden and spacing then lets you make other estimates or assumptions, namely for the length of stemming (and, in the case of a shaft sink, the length of sub-drill) to give you the total length of charge in the shothole. You would normally plan, with this separation, for stemming length to be equal or greater than the burden, say 700mm because this is a low-risk situation. So, if the round is 1.8m deep, the length of charge is 1.8m – 0.7m stemming = 1.1m of charge. Because you know the diameter of the shothole and the length of charge you can find the total amount of explosive in the shothole – for explosives of different densities – by using a loading density table. Later, we’ll use the example of a medium-risk situation in which case you’ll need to use Powergel Permitted 3000, and you are restricted in the amount of explosive per shothole.

You arrive at a design for a 4m wide face, 3m high as shown in the following diagram.

Diagram 4: Tunnel round in low-medium risk stone

This face has a volume of 3m x 4m x 1.8m = 21.6m3.

Step 2. Calculate the weight of explosive in each shothole

Using a loading density (or charge weight) table – see Diagram 5 below - you would see down the left hand column the diameter of 38mm, and you’d go across that row until you get to the column headed 0.95g/cc for pressure-loaded ANFO (remembering that this is a low-risk situation), to find that 1.08kg of ANFO is pressure-loaded into a 1m length of a 38mm diameter hole. But you’ll be charging 1.1m of the shothole, so you’ll have 1.1 x 1.08kg = 1.2kg per hole.


Step 3. Calculate the total weight of explosive

There are 37 shotholes, each with 1.2kg of explosive, so the total weight of explosive is = 37 x 1.2 = 44.4kg.

Step 4. Check the powder factor (as a reality check)

You are using 44.4kg to break 21.6m3, so the powder factor is = 44.4kg / 21.6m3 = 2.06kg/m3. This is the sort of powder that is typical of tunnels in this sort of rock so the design has probably made the right assumptions for the pattern and adjusted suitably for the desired opening.

If you’d drilled this out for ANFO and suddenly found the holes were making water, changing your explosive to an emulsion with a higher density, say 1.25g/cc, you’d have more weight of explosive in the shothole. In this

case you’d go down the left hand column of your loading density table to the 38mm diameter row and across the row until you got to the column headed 1.25g/cc, to find that now you’d have 1.1 x 1.42 = 1.375 or near enough to 1.4kg/metre for each charged shothole. You would now have a total weight of 37 x 1.4 = 51kg of emulsion in the blast. Recalculating the powder factor now gives you 51kg / 21.6 m3 = 2.4 kg/ m3, which is higher than with ANFO, so the environmental impacts will be more noticeable.

Hopefully, you would have found the wet holes before you’d gone too far with the drilling and you would have spread out your holes to account for the higher strength explosive. The shotholes could have been spread out in rough proportion to the increased density = [1.25 / 0.95] x 0.7 = 900mm.

Loading density tables indicate the weight of explosive it would take to fill one linear metre of shothole of a given diameter for a given density of explosive. Using a hole of 102 mm and an explosive density of 0.8 gm/cc (pour-loaded ANFO), the loading density is 6.54 kg/m (that is, for this diameter of shothole you can pour 6.54kg of ANFO into a shothole and it will fill 1metre of the hole).

The weight of explosives to be placed into each shothole

= length of shothole to be charged x loading density

= 8m of charge x 6.54kg for every metre of charge

= 52.32 kg total in the shothole

Diagram 5: Shothole Loading Density Table (Orica)


By knowing the powder factor which indicates the weight of explosive it takes to break one cubic metre of rock, you can calculate the volume of rock which one shothole can break. So, if it takes 0.35 kg of explosive to break a cubic metre of rock at this quarry, then 52.32 kg (in one shothole) will break 52.32kg / 0.35kg for every cubic metre = 149.5 m3.

Case Study 2

Designing a stone roadway blast in a medium-risk situation

In a medium risk situation you could still use a burn cut as before. However, you must now use Powergel Permitted 3000 and restrict your charge weights to less than 1200g per shothole. This means that each shothole will have three cartridges, each weighing 370 g = 1.1kg per shothole.

You still have 37 shotholes, so the total charge weight is now = 37 x 1.1kg = 40.7kg, and, since this is still required to break 21.6m3, the powder factor becomes = 40.7kg / 21.6m3 = 1.9kg/m3, which is now becoming, potentially a bit light, so you might end up with butts or drill sockets left in the face.

Case Study 3

A development heading or tunnel underground

This case study illustrates the same calculations for a typical round in zero risk conditions; it will be used to compare a method that uses charts. Your drill rig drills holes that are 45mm in diameter in a tunnel face, and you are going to pull a round 3.6m deep - so what is your powder factor?

The normal ratio between shotholes where the rock moves parallel to the drillhole is 20 times hole diameter, so in this case your spacing on average will be 20 x 45

= 900mm

Looking at the loading density table for 45mm holes, with pressure-loaded ANFO at a density of 0.95g/cc you will be loading 1.5kg of ANFO in every metre of the shothole charge. This means that a shothole 3.6m long (and charged to 500mm from the collar), will have a charge length of 3.6 – 0.5 = 3.1m, and 3.1m x 1.5kg/m

= 4.65kg in each shothole.

Each shothole is responsible for shattering and moving a block of rock that is 900mm x 900mm x 3.6m

= 2.916m3.

A powder factor will be 4.65kg / 2.916m3

= 1.6 kg/m3, which is lower than the normal average 2kg/m3, but you will have additional cut-holes that are charged. Note that if you’d charged to the collar, the powder factor would have been 1.85, so a figure of 2kg/m3 is ideal for planning purposes – for example, a drive round that is 5m wide x 5m high x 3.6m deep has an overall volume of 5x5x3.6 = 90m3, and you need 2kg of ANFO for every m3 so you’d need to get the nipper to bring 2 x 90 = 180kg or 8 x 25kg bags, say 9 bags to be safe (and you’re likely to spill a bit).

Case Study 4

Underground tunnel or drive heading

This is a different way of designing a blast in a tunnel to the earlier case study. It uses a Table rather than the ‘rules of thumb’ that you used earlier. In this case study, we are assuming the tunnel is for a civil construction project involving soft or weathered granite. A drive is to be excavated with dimensions 5m wide by 4m high in weathered granite using 45mm diameter shotholes and an advance of 3m per round. You are going to use explosive cartridges of 38mm diameter for primers, with all holes charged with pressure-loaded ANFO primed by 200 mm emulsion explosive (260 g per cartridge). Note; in reality, you’d probably charge the lifters with long cartridges of emulsion due to these holes being wet, and you’d lightly charge the perimeter holes, but these are not going to change the calculations or design in any significant way.

Calculate the:

1. number of shotholes

2. in-situ volume per round

3. loading density per hole

4. weight of explosives per round

5. number of priming charges per round

6. number of long delays required per round

7. burden and spacing of the shotholes.


1. In tunnel rounds a typical ratio for hole spacings is 20 times hole diameter, so in this example, this would be 20 x 45mm = 900mm. For a drive heading 5m wide this would mean (5m / 900mm spacing per hole = 5.6 holes, rounded up to 6 holes, plus one for the wall) = 7 gridlines across the face with one gridline up each wall, allowing for wall holes to be more lightly charged. Similarly, for a drive of 4m height this would mean (4m / 900mm per hole = 4.5 holes = 5 holes plus 1 for the lifters) = 6 grid lines and this allows for back holes to be more lightly charged. In reality there will be extra holes around the cut to make sure this part of the round comes out easily. So you would have 7 x 6 = 42 holes plus an extra four around the cut holes, totalling 46 holes. This is relatively easy to see for a rectangular drive heading but is the same end result for all shapes. However, another way of calculating the number of shotholes is to look at Diagram 2g, which shows the number of shotholes for different rock types, taking account of the different powder factors for different rock types. From Diagram 2g, the number of holes for a face area of 20m2 in granite is 45 holes, which is almost exactly what you’ve estimated so continue the calculations using 46 holes.

2. In-situ volume per round is:

= face area x advance = 20m2 x 3m deep

= 60 m3

3. A standard drive round requires 2kg explosive for every cubic metre of rock. Other experience, see Diagram 2h, suggests that the powder factor for a 20m2 area in granite is about 2.5 kg/m3, so use this powder factor for design purposes and be prepared to adjust it in light of the results you’re going to get.

4. Weight of explosive per round is:

= in-situ rock volume per round (m3) x powder factor (kg/m3) = 60m3 x 2.5kg/m3 (that is, for every cubic metre of rock you’ll need 2.5kg of explosive, and you’ve got 60cubic metres of rock to blast, so 2.5 x 60 = 150)

= 150 kg of explosive for the round (which means that you’d get the nipper to bring 7 bags of 25kg ANFO for the round just to be on the safe side even though you might only need 6bags. You could also estimate for 46 holes that there will be 150kg / 46holes = 3.26 kg per hole)

Loading density per hole is – from Loading Density Tables, with pressure loaded ANFO with a density of 0.95 and hole diameter of 38mm:

= each shothole will require 1.08kg of ANFO for each metre of charged length, so for 3.26 kg explosive you’d need to charge 3.26kg /1.08kg/m = 3m so you’ll need to charge each shothole up to the collar. Alternatively you could add more holes and change the spacing a bit – for example closing up the spacing from 900 to 750mm for the ring of holes around the cut box-holes and closing up the spacing from 900 to 800mm for the ring inside the wall holes.

5. The number of priming charges required is 46.

6. The number of long delay detonators is 46 plus about 25m of detonating cord trunkline and one electric detonator to initiate the circuit, requiring bell wire to connect to the firing cable.

7. Use graph paper to locate the shotholes on a drill plan.

Case Study 5

Trench blast

You have been asked to blast a trench in solid, massive (homogeneous) basalt on the surface of your underground coal mine, with a design width of 0.5 m and a depth of 1.5 m (see Diagram 5), and situated about 40 m from the closest residence. The total length of the trench needs to be 100 m. There is no topsoil, and a subgrade of 200 mm has been used successfully before. You have a rock drill capable of drilling 38 mm diameter holes. Your standard explosive is 25 mm diameter by 200 mm explosive cartridges, having a weight of 150 g each. The powder factor for this type of rock and size of trench is 1 kg/m3 (which is in the mid-range for trenches).


Diagram 6: Trench dimensions

Commence this calculation on the first metre length of trench.

The volume of in-situ rock to broken at the required grade line in the first 1m is:

= in-situ volume = length x breadth x depth

= 1m x 0.5m x 1.5m

= 0.75 m3 (for one metre of trench)

The amount of explosive required for each metre of trench is:

= weight of explosive = powder factor (kg/m3) x volume (m3)

= 1kg/m3 x 0.75m3

= 0.75 kg (= 750g)

Equating this to 25 mm diameter x 200 mm cartridges is:

= number of cartridges = weight of explosive per metre of trench divided by the weight of a single cartridge (150g)

= 750 g/ 150 g per cartridge

= 5 cartridges (per 1m length)

Because the trench is only 40 m from a house, you can:

1. drill and fill one shothole with 5 plugs with a burden of 1 m, as shown in Diagram 5, or

2. drill two shotholes in a staggered pattern and load the holes with 2.5 cartridges each, as shown in Diagram 5, or

3. deck-load the two shotholes with 0.3 m of stemming, to distribute the explosives energy over the full length of the hole.

The single-hole blast is satisfactory in soft rock and with trenches having a narrow width. The edges and toe will be very uneven. If all of the explosive required for that 1m length will not fit into one shothole, two or more shotholes will be required. The holes are staggered to give smoother trench walls. Such patterns are more common where rigid pipes are to be placed in the trench. This pattern is useful in wider trenches.

The total number of holes required using a staggered hole pattern is:

= holes per metre of trench x length of trench (m)

= 2 x 100

= 200 shotholes

The total amount of explosives required is:

= explosive weight per metre of trench x length of trench

= 0.75 x 100

= 75 kg

In all of the three methods use delays to allow progressive relief and to control ground vibration.

The total volume of rock to be blasted is:

= in-situ volume of rock per metre of trench x length of trench

= 0.75 x 100

=75 m3

The position of the shotholes can be placed on a plan and adjusted as the blasting progresses to obtain the best results. A trench is normally loaded by distributing the explosive charge along the full length of the hole, and is initiated using either instantaneous or millisecond delays.

Case Study 6

Shaft sinking blast in a zero risk shaft

This case study illustrates that there are many ways to work out how you are going to design and plan a blast. A 5m diameter circular shaft is to be excavated in basalt to a depth of 150m. Your chosen powder factor is 4kg/m3, which is at the top end of the range of powder factors for


shaft sinking because it is only 5m in diameter making it a tighter shot than a larger diameter shaft. The density of the bulk emulsion explosive is 1.2 gm/cc. Each round has an advance of 2 m. Calculate the following per round:

1. number of shotholes

2. in-situ volume of rock to be broken

3. diameter of the shotholes

4. total amount of explosive required

5. total number of priming charges

6. total number of detonators

7. determine the location of these holes in a drill plan.

1. From Diagram 2k, the average number of shotholes would be 70 for medium-strength rock.

2. The in-situ volume of rock per round is:

= π x (radius)2 x advance = π x (2.5m x 2.5m) x 2m

= 39.3 m3

3. The weight of explosive per round is:

= in-situ volume per round x powder factor = 39.3 x 4kg/m

= 157 kg

Weight of explosive per shothole required is:

= 157 / 70 shotholes in the round

= 2.25kg per hole

Weight of explosive to load 1m of shothole is:

= 2.25kg / 2m

= 1.125kg/m

4. From the shothole charging density tables, it will take 1.36 kg/m of emulsion (with a density of 1.2 g/cc) to fill a 38 mm diameter hole, so 38 mm diameter shotholes would be suitable.

To get the total amount of explosive required for the shaft sink first find out how many rounds because you’ve already worked out how much explosive is required for each round:

= depth of shaft / length of each round to get the number of rounds

= 150m / 2m per round

= 75 rounds

so, total amount of explosives required for the shaft sink:

= explosive per round x no. of rounds = 157 x 75

= 11,775 kg

5. Only one primer per hole would be required, so the number of priming charges per round is 70.

6. The number of long-delay detonators per round is 70, because you’ll have one per hole.

7. To locate the shotholes on a drill plan, determine the number of holes for the cut, and equally space the remaining holes over the shaft area. If the blast impact and the ground conditions make the shaft walls a bit ragged, you can always place additional holes on the perimeter for a smoother finish.

There are formulae and computer programs that give a reasonable burden and spacing, but the most practical solution is to plot the shotholes on graph paper, starting with an approximation for spacing of 20 x hole diameter = 20 x 38mm = 760mm because its like a tunnel round where the rock is mostly going to fly parallel to the shotholes. Modify the burden and spacing with each consecutive blast until the desired result is achieved. Note that the burden on the shotholes can be increased as the drill pattern moves away from the cut, but you might shorten this up for the last ring because you might decrease the explosive in each hole around the outside. Where a large-diameter rectangular shaft is required, a wedge cut would be suitable.


For shaft-sinking, half-second or long-delay detonators are required to provide sufficient time for the rock to fracture and move between delays. Without a sufficient delay time, the broken rock will choke, resulting in a poor advance with a very rough face, making digging as well as subsequent drilling very hard.

LEARNINg & ASSESSMENT TASK 4.2 qUANTITIES OF EXPLOSIVE REqUIRED

Assessment

Go to Learning & Assessment Task 4.2 in your Learners Workbook 4 “Blast Planning & Reporting”. Calculate the powder factors used in at least two different types of blasts on your site; calculate this powder factor as the weight of explosive in kilograms per cubic metre of rock and compare your result with typical relationships for quarry/stope blasts or tunnel/drive headings. (Note: some sites refer to powder factors in terms of kilograms of explosive per tonne of rock, so for the purposes of this assessment task you will need to convert this from kg/t to kg/m3; if you need help doing this ask your supervisor or ask someone for the density of the rock to convert tonnes to cubic metres.) Comment on the difference or similarity in the powder factors on your site, compared with typical powder factors, and explain the difference or similarity.


03IDENTIFY THE MAXIMUM INSTANTANEOUS CHARgE & DELAYS

3.1 KNOWINg WHETHER YOU ARE RESTRICTED IN THE AMOUNT OF EXPLOSIVE FIRED ON ONE DELAYIn the previous section we discussed the quantities of explosives required in a blast. Airblast overpressure and ground vibration restrictions or limitations imposed by government regulators may dictate the ‘maximum instantaneous charge’ that can be fired on a single delay; and is generally determined by the distance from your nearest neighbour. This will in turn influence hole diameter and length. It is unlikely to impact on blasting underground in solid coal, but it could have an impact on your shots in stone, especially if you’re near the surface such as with a shaft sink or commencing a drift, and it will almost certainly impact on any blasting you do on the surface.

Maximum Instantaneous Charge (MIC) is the maximum explosive charge initiated at any instant of time, which normally means the amount of explosives going off on any one delay during the blast. In practice this means within 8 milliseconds of another charge. It is called the ‘Effective Charge Weight per Delay’ in AS2187.2 and is the most common restriction applied to blasting at a site.


Calculate the permitted MIC in a blast design by knowing:

Face height Metres (m)

subdrill Metres (m)

Total drill depth Metres (m)

stemming depth Metres (m)

explosive column length Metres (m)

Hole diameter Millimetres (mm)

weight explosive per meter of hole

Kilograms (kg)

weight of explosive per hole

Kilograms (kg)

selected powder factor Kilograms per ‘bank’ cubic metres (kg/m3), BCM

volume of rock per hole Bank cubic metres (m3) (weight of explosive per hole x powder factor)

surface area of drill pattern

square metres (m2)

divide the volume of rock per hole by the face height

drill pattern

- square - Rectangular - staggered

Calculated for the surface area of the drill pattern

Burden Metres (m)

spacing Metres (m)

3.2 REMEMBERINg PUBLIC SAFETY, TOOHigher powder factors increase the risk of flyrock. When selecting a powder factor consider:

1. Environmental constraints (imposed on the site under licence conditions)

2. Airblast overpressure

3. Ground vibration

4. Proximity of buildings and structures

5. Risk of flyrock.

This might be an issue if you were to destroy explosives by burning on the surface, because you will assume that a detonation might occur.

3.3 THINKINg ALSO ABOUT THE TIgHTNESS OF THE SHOT & THE ENVIRONMENTAL CONSEqUENCESEven if you are not restricted to a certain weight of explosive to be fired per delay you might want to think how the shot will fire and the environmental consequences if the shot is a tight one. A tight shot will probably result in higher than expected ground vibrations, or flyrock or noise. A blast that is confined such as in a shaft, will require a higher powder factor than an open face in a quarry. The objective is to select the lowest (and hence most economical and community-minded) powder factor to meet all the above requirements. This is just the same as the earlier discussion on adjusting the rule of thumb for holes spaced apart at varying distances depending on the tightness of the shot.

Important

For each blast pattern, the powder factor will vary with the face height or geometry, and, consequently the tightness, of the shot varies.

3.4 ADJUSTINg YOUR RULE OF THUMB FOR SITE EXPERIENCEAs a starting point for blast design assume that all the commonly available explosives give the same results weight for weight. Experience gained in a particular project may show that one type of explosive is more effective than another type and allow a reduction in the powder factor required to achieve the specified results. Two important concepts to understand are:

1. The shock impact from the blast (sometimes called ‘brisance’) - this is the ability of an explosive to shatter rock by shock or impact as distinct from gas pressure


2. Gas pressure (sometimes called ‘heave’) - this is the extent to which the broken mass of rock is moved from its original location.

High shock (high brisance, or high shattering effect) is important in breaking very strong rocks into small rocks, which is vital in shaft sinking, while heave (caused by gas pressure) is important in softer rocks and to provide a good muckpile for loading out, such as in a drift.

Important

After selecting a powder factor for a new project, always undertake a small trial blast to ensure that the desired environmental, safety and fragmentation results are met.

The number of drill holes required can be calculated by dividing the required quantity of rock by the volume per hole. These holes can then be laid out for drilling using the burden and spacing calculated commonly by assuming the burden and the spacing are the same. In reality they may be a little different due to the final size of the area to be blasted – especially in civil construction, such as in a tunnel. The available face length will determine the number of rows required for the calculated number of holes.

Controlling the MIC is a concern when designing a blasting sequence.

3.5 IDENTIFYINg EXPLOSIVE qUANTITY PROBLEMS & POSSIBLE SOLUTIONS

Problem Possible solution

excess back-break Decrease burden, increase explosives column height–may spread pattern to maintain powder factor. Change direction of face.

Rocks excessively scatter

Increase burden.

Rocks come out, but fragmentation poor

Decrease burden. Increase powder factor

excess back-shatter Decrease burden. Increase delays between rows.

Toe between holes Decrease hole spacing.

High bottom Increase hole depth, use heavier bottom loads.

Boulder in front of pile

Use back-shatter solutions.

Boulders on top of pile

Increase explosive column height.

Boulders on floor Treat as toe problem.

Boulder within pile, good fragmentation

Misfires, poor explosives performance, inaccurate drilling so deal with each or any of these.

Diagram 7: Summary of solutions to improve blasting

3.6 SELECTINg THE SHOTHOLE PATTERNSelecting a shothole pattern depends on the rock type being blasted and yield the rock product required. Explosive manufacturers have conducted extensive blast monitoring, analysed blast results and have a wealth of information to advise and assist in the selection of a blast pattern for a given application and rock conditions. A blast pattern is refined by careful observation of many blasts and modification or fine-tuning of blast-design


parameters such as spacing, burden, subgrade and delay sequence. Patterns help reduce the number of holes going off on any one delay, which is one of the best ways of reducing ground vibration and airblast overpressure.

In stone, the minimum distance between shotholes depends on the level of risk, but as a rule of thumb you might make them 700mm (roughly 17 times hole diameter) and never closer than 500mm for the bulk of the holes and no closer than 250mm for burn cut holes – this depending on the level of risk of a methane or dust explosion. Burn cuts should not be used if there is any risk of methane or dust explosion, in which case you would want to use a drag (or fan-cut) round with a minimum of 400mm between the closest explosives which is probably in the bottoms of any holes. The collars of the drag (or fan-cut) round might be 300mm apart but they won’t have explosives in them until the diverging shotholes are at least 400mm apart.

Diagram 8: A blast pattern for a medium risk roadway round in stone

The MIC in this round would be ten holes on the No. 9 delay so, if the charge in each hole were three cartridges of Powergel Permitted 3000 at 370g per cartridge, the MIC = 10 x 3 x 370 = 11.1kg.

3.7 PLANNINg THE BLAST DELAYA sequence for firing a drift round is shown by the numbers in the diagram above. The burn cut helps develop a free face by opening up the uncharged reamer holes. Having the three delays in the burn cut allows the cut to open up progressively. The next round might have the cut on the right hand side to reduce the problem of not drilling into old butts or drill sockets.

Delayed blasts give better fragmentation than a simultaneous blast because it allows for better fracturing. Lower ground vibration levels should be expected because there is less energy released than the simultaneous blast. On the negative side, a large time delay may interfere with the adjacent explosive charges or prematurely fragment the rock around them and cause ground to slide or cause cut-off.

3.7.1 BlAsTInG usInG delAYs

In a properly designed multi-delayed blast, charges adjacent to free faces have an appropriate burden of rock to fragment and displace. Shotholes in consecutive rows depend on the firing of earlier charges to create new free faces during the blast. If a free face is not created, the charge will tend to crater upwards to the nearest free face – and may result in a blow-out. It is standard practice, but is particularly important in shooting coal underground, that that the shothole with the shortest burden is fired first. Remember, do not use a zero number in the series in the same shot as other numbers – because the zero might detonate before the other detonators have started to burn their delay elements and cut off the circuit – without a zero, all delay elements are burning before the first shot detonates so a cut-off is not a risk.

The delay times between adjacent shotholes in rows of shotholes are referred to as the intra-row delay. This period of time is required to allow the blast to occur at a designated point and for the ground to move creating new faces, before the next set of shotholes initiate. For a brittle, elastic, homogeneous rock type, a short intra-row delay is usually appropriate. By contrast, a porous, plastic, jointed rock mass, would require more time between detonation of adjacent shotholes. Typical intra-row delays for conventional blasting is 4-6 milliseconds per metre of shothole spacing, measured along a row.

Delays between rows are usually in the range of 10-12 milliseconds (ms) per metre of effective burden - the ideal delay is influenced by design parameters. For example, a deep shot needs longer delay intervals than a shallower blast.

In practice, this means when you are shooting in coal underground the delay interval is the 30ms nominal time delay between numbers in the series of permitted detonators. However, you will need to conduct a risk assessment when you are shooting in stone to rate the risk of a dust explosion by having a number of shots going


off in a sequence – in some cases, such as when you commence a shaft sink, you won’t have any gas or dust around, while in other cases, such as drifting between faulted seams, you will be very close to coal dust and methane, so your level of ventilation as well as your level of stone-dusting is clearly important in your risk ranking. Depending on the level of risk you might want to minimise the risk by limiting the number of delays used so the whole blast goes off within, say 300ms.

In blasting solid coal the delay between successive shots must be the delay between successive numbers in the permitted detonator series, nominally 30ms – any longer runs the risk of firing into a cloud of coal dust, which could be ignited by a blow-out. The time interval between the first and last shot in coal (again, to reduce the risk of a dust explosion, but this time by minimising the risk that a dust cloud might hang suspended in the air in the presence of shots) should not exceed 125-150ms so the number of delays used in sequence would be limited to four.

Important

The blast delay sequence in underground coal shotfiring should be decided after the holes have been drilled and the site inspected (for accuracy of shothole drilling).

LEARNINg & ASSESSMENT TASK 4.3 - MIC & DELAYS

Assessment

Go to Learning & Assessment Task 4.4 in your Learners Workbook 4 “Blast Planning & Reporting”.

Examine the copies of blast plans or standard blast designs that you have already obtained, and check that the delays are shown on the plans. These delays may be shown as the order in which each hole fires, or as the delay period, or as the delay after the shot is initiated.

Check what is the largest number of shotholes that will be detonated on any one delay.

Calculate the weight (in kilograms) of explosives in each of the holes that are fired on the same delay and multiply this by the number of shotholes to work out the MIC (or total weight of explosives per delay).


04MONITOR ENVIRONMENTAL IMPACTS

4.1 BEINg AWARE OF ENVIRONMENTAL DISTURBANCESA shotfirer/explosives user must produce acceptably fragmented rock in a muckpile that is suitably shaped for ease of loading, while at the same time minimising unacceptable airblast overpressure, ground vibration, flyrock, and overbreak. These activities must be done safely, and in an appropriate timeframe, without misfires. You must know the causes of environmental disturbance from blasting, the likely reaction from individual neighbours, and the procedures for controlling the disturbance. Everyone assisting in blasting operations should be made aware of these controls, and should be trained to implement procedures for risk control and monitoring.

The continued operation of your site may well depend on fully considering the possible effects of each blast on the environment; not doing so will result in work slowing down if not stopping, the involvement of one or more government or statutory authorities, and the imposition of higher costs due to unscheduled delays or the use of more costly methods to do the same work. Ultimately it may also result in the loss of a valuable resource.

The community needs to be assured that blasting activities will be managed responsibly, and that there will be minimal disturbance to their lifestyle and no damage to their property. Even if the mine, for instance, was established before residents moved into the area, this does not give the operation an advantage in law or in any negotiations, or the right to offend others. Furthermore, every person has common law rights, which in basic terms means that no other person has a right to offend them on their property, or to damage their property. If offence, or property damage, is caused, people may take the matter to a civil court and seek compensation against the users of explosives. Compensation for damage to property from ground vibration is well-established in our legal system. If the offence is proven, the site and/or shotfirer may be required to pay a fine or be sent to gaol, and the shotfirer may be required surrender his/her ‘ticket’.


Environmental disturbance is regulated by both health and safety legislation and environmental legislation. Underwater blasting poses additional problems, and is perceived by the water-loving public as an impost and inconvenience, when they are requested to move out of the water for blasting to proceed. Wet strata can exacerbate ground vibration problems.

Reference

AS 2187.2 contains additional information on environmental considerations. For underwater blasting contact relevant government agencies, for example in NSW to DPI/Fisheries and/or NSW Maritime Authority.

4.2 IDENTIFYINg CAUSES OF DISTURBANCEBlast disturbance is generally caused by the following factors:

1. flyrock

2. dust

3. noise

4. blast overpressure

5. ground vibrations

6. concussion from underwater blasting.

The order of impact will depend very much on the location of neighbours, their lifestyle, status, their activities during the blast and their perception of acceptable disturbance, damage or other factors.

4.2.1 FlYROCk

Flyrock may be a problem if you are starting off a shaft or drift. Flyrock is any rock or debris that becomes airborne as a result of a blast. Flyrock is not a problem if it remains within the blast area. Rock from a drift or shaft-sink blast may become airborne because of gas energy (heave) exerted onto fractured rock. Gas energy can escape through a small opening, such as the collar

of a shothole or due to jointing planes in the rock mass being orientated in a direction that enables a blow-out, before the gases can heave the bulk of the rock that is fragmented.

Concentrated energy may cause loose stones to be projected surprising distances, sometimes in clusters. This is an extremely dangerous situation and must be avoided. Some factors contributing to the occurrence of flyrock, are:

a. major geological faults

b. initial hole burden less than adequate

c. short stemming depth

d. initiation sequence fails to allow for rock movement before successive holes detonate

e. shothole diameter too big compared to the burden

f. blast pattern shape causes holes to choke off

g. stemming material – inadequate or too fine

h. powder factor too high.

There are other sources of fly material, such as brick or glass from buildings being demolished, wood and tree roots from tree stump blasting in clearing land for the mine and its infrastructure. In these situations, excess explosive may be the major factor in causing fly material. When fly material leaves the boundary of the blast site, it has the capacity to severely damage property and cause injuries by direct impact. It is potentially the greatest hazard from blasting, and, in some cases, pieces of flyrock and debris have travelled over 800m from a blast to land on motorways, neighbouring residential areas, recreation areas and industrial sites. Even with controlled blasting by experienced operators, flyrock from one documented demolition blast exceeded the safety limits set by the shotfirer/explosives user for observers, and one person was killed and four people were severely injured.

In general, legislation requires that flyrock be contained within the blast area. Wherever blasting is carried out in populated areas, in close proximity to any public road or pathway, or in any other circumstances where risk to injury to persons or of damage to property would result, the area to be blasted should be covered on top and sides with blasting mats or other approved materials to prevent stones or debris from being projected. All flyrock incidents should be reported to the appropriate


authority who investigate the cause and decide whether legal action is warranted. The controlling authorities for flyrock or debris in underground coal mines in NSW is the Department of Primary Industries / Mineral Resources.

Reference

AS 2187.2 contains useful reference material regarding flyrock.

4.2.2 dusT

Dust from blasting is created by:

a. fracturing of new rock surfaces

b. initial ground movement at a blast

c. impact of falling material on the quarry floor

d. eventual escape of stemming from former shotholes

e. nature of the rock

f. powder factor used in the blast; overcharging can reduce stone to powder (and generate flyrock!).

Although the community will tolerate some dust, it must be managed, or there will be complaints including soiled washing, dust entering premises through windows and doors, motor vehicles covered with dust and plant contamination/damage. Another serious dust problem occurs during the drilling of shotholes, especially for people working on site. The drilling and hammering effect of the drill creates considerable airborne dust. As most rock, especially sandstone, contains some form of silica, the driller or any one else in the vicinity may contract silicosis, a serious lung disease caused by inhaling liberated dust. If this dust drifts over residential areas, the same concerns arise. Wet drilling or the use of dust extractors overcome this problem and there are strict legislative controls regarding this, with high penalties for offenders.

4.2.3 ‘nOIse’, OR AIRBlAsT OveRPRessuRe

When a blast initiates, energy is released into the atmosphere at pressure levels much greater than atmospheric pressure. This energy travels away from the blast site as a pulse or wave front, fluctuating between pressures above and below atmospheric pressure, and

reducing in strength with increasing distance. Sound also travels through air in wave-form and its magnitude reduces with increasing distance until it can no longer be heard.

Noise, strictly, is a collection of sounds that can be detected by the human ear. The human ear is capable of detecting sounds with frequencies ranging from 20 to 20,000 hertz (Hz, or cycles per second). Although the human ear can detect a wide frequency range, not every person will have this ability, because of degrees of hearing loss. To a person not expecting a blast, the ‘noise’ is sudden, sometimes loud and different from other noise in the environment. It is often described as a thunderclap. ‘Noise’ from blasting is generally in the low range, below the capacity for humans to hear, so the noise as measured at the home of a resident is called airblast overpressure, or airblast. You can often feel the noise as pressure on your face or clothes rather than actually hear it. If you actually hear the blast you are probably hearing secondary noise caused by the airblast overpressure. For underground mines the airblast coming out of the shaft or decline will be similar to the sort of noise from your music system’s sub-woofer – that you feel more than hear. Neighbours will hear secondary noise – the window rattling or glasses shaking on a shelf.

Airblast depends on weather conditions; a strong wind blowing directly towards a neighbour’s house will make the noise from a blast a lot louder at that house than if it were blowing in the other direction. Other weather conditions such as very low cloud cover, or a temperature inversion also make noise louder than normal. Dense fog can transmit airblast better than clear air. Weather conditions play a significant part in the transmission of noise or airblast. Other factors that you should consider are:

a. Exposed explosives – such as detonators and detonating cord that is uncovered

b. Poor stemming

c. Blow-out arising from geological weaknesses

d. Blast shapes that result in the last rows of holes being choked off causing them to blow up rather than out.

‘Noise’ originating from blasting is controlled in NSW by the Department of Environment & Conservation (formerly the Environment Protection Agency, EPA). Conditions in licences are applied to blasting. The maximum blast overpressure limit that is commonly applied in NSW for


comfort is 115 dB (linear) for 95% of blasts and a top limit of 120dB(lin) – for no more than 5% of blasts. For preventing damage to buildings and structures AS 2187.2 recommends a limit of 133 dB(linear). Blast design should always plan to keep airblast below 112dB, which is half the pressure of 115dB, and preferably below 109dB, which is half again - noise is measured on a logarithmic scale.

Ground vibration normally arrives before the airblast, because solid earth is a better conductor than air. However, an upset person will often perceive these arrivals as one event, and generally complain about both. With some careful explanation, it may be possible for them to distinguish between the arrival of ground vibration and the later air disturbance associated with noise.

Reference Support

1. AS2187.2 contains useful information on monitoring airblast overpressure and ground vibration.

2. By this stage of your development in shotfiring you will have obtained a copy of that Standard, so we will not duplicate that material here.

3. Make sure you have the right equipment to monitor for these two environmental impacts.

4. Also make sure you have the equipment calibrated from time to time, so that you may be confident when dealing with complaints.

Where you anticipate that some ‘noise’ may be experienced, make an estimation of the levels of disturbance from a blast, which you might want to test with some trial shots.

Case Study

To estimate airblast overpressure in kPa

Airblast overpressure from an unconfined charge on the surface can be estimated by the following formula:

ABOP(unconfined) = 185 x 103 [ W0.333 / D ] 1.2

Airblast overpressure from a confined charge on the surface can be estimated by the following formula:

ABOP(confined) = 3.3 x 102 [ W0.333 / D ] 1.2

where:

ABOP is the estimated airblast overpressure at a location from a blast (kPa)

D is distance from the blast (metres)

W is the total mass of the charge detonated (kg)

Airblast overpressure (ABOP) can be converted to dB (linear) using the formula:

Lp = 20 log 10 [ P / P0 ]

where:

Lp is the airblast overpressure (ABOP) level expressed in dB (linear)

P is the airblast overpressure (ABOP) expressed in Pascals (Pa)

P0 is the reference pressure which equals 20×10-6 Pa.

As you can see, and this should not be surprising, confined charges decrease blast overpressure.

damage limit Response

0.002 kPa = 100 dB (linear) barely noticeable

0.006 kPa = 110 dB (linear) readily acceptable

0.05 kPa = 128 dB (linear) currently accepted that damage will not occur below this limit

Diagram 9: Airblast damage criteria

Limits for comfort as commonly prescribed equate to pressure values as:

0.01 kPa equals 115 dB (linear)

0.02 kPa equals 120 dB (linear).

Reference

For further information about monitoring of blast overpressure, refer to AS 2187.2.


4.2.4 GROund vIBRATIOns

When a blast initiates, energy is distributed equally in all directions. Most of the energy should be consumed in breaking rock or doing work, but a small part of it (depending on the tightness of the shot) would be dissipated into the environment. If the blast is well-designed, ground vibration will be minimal. Ground vibrations originating from blasting consist of complex wave forms, some of which travel on the surface and others through the body of the rock. Ground vibration transmission through rock is influenced by:

a. type of rock

b. continuity of rock

c. faults, dips and schistosity

d. saturated sand beds

e. water tables.

Where there are no buildings or structures, the only effect of the ground vibration is to cause people in the vicinity to feel a movement beneath their feet. Their response to these ground vibrations depends on their attitude and position relative to the blast, and their activity. Ground vibration often goes unnoticed if kept within limits.

Ground vibration greater than the prescribed comfort limit may cause concern to the unsuspecting householder. The psychological effect of an unexpected explosion appears to magnify the sensation of vibration. It is difficult to convince a householder or owner of a building that no damaging vibration has occurred when the alarming noise of the explosion was heard. Ground vibration may also cause secondary noise when windows and glass shelves in neighbouring homes begin to rattle. When the blasting is in a built-up area, ground vibration can assume a major significance.

Excessive ground vibration may cause superficial and structural damage to dwellings and structures, and disrupt the operation of sensitive equipment in hospitals for example. Recorded damage from blasting has been often catastrophic, such as the tripping-out of computers and other equipment, and the failure of large water storage dam in Europe. In multi-storey buildings, the magnitude of vibration may increase significantly with increasing height of the building.

Ground vibration is regulated in NSW by the Department of Environment & Conservation who issue licences that limit ground vibration. These licences provide comfort limits for ground vibration for various days and times of the week, and other conditions for minimising the impact on persons. These conditions and limits are a general guide and may be altered by the authority for specific locations. Typical limits are 5 mm/s at the property of a resident for 95% of blasts and up to 10mm/sec for the other 5% of blasts.

The maximum ground vibration limit for damage recommended by AS 2187.2 is 25 mm/s for commercial and industrial buildings or structures of reinforced concrete or steel construction and 10 mm/sec for houses and low-rise residential buildings, subject to conditions. Blasts are normally designed to be below 2mm/s. There are formulae to estimate ground vibration from a blast. A chart from AS2187.2 Appendix is included in Diagram .. as an example of the help used in designing blasts; note that AS2187 uses the term ‘effective charge weight per delay’ rather than MIC, but you can use either term.

The maximum ground vibration limit for damage recommended by AS 2187.2 is 25mm/s for commercial and industrial buildings or structures of reinforced concrete or steel construction and 10 mm/s for houses and low-rise residential buildings, subject to conditions. Blasts are normally designed to be below 2mm/s. There are formulae to estimate ground vibration from a blast. A chart from AS2187.2 Appendix is included in Diagram 10a as an example of the help used in designing blasts; note that AS2187 uses the term ‘effective charge weight per delay’ rather than MIC, but you can use either term.


Diagram 10a: Estimating ground vibration from blasting at distances from structures (from AS2187.2 Appendix J - 2006)

By way of example, if you were going to fire a shot in which the MIC (or the ‘effective charge per delay’) was 100kg, then any structure closer than 100m is at risk of damage because it is likely to have a ground vibration that exceeds 25mm/s. Going further up the effective charge per delay line (at 100kg), any structure closer 200m is likely to have a ground vibration of 10mm/s so people at that structure are likely to complain, and sensitive instruments may be affected. Similarly, any structure at 300m is likely to have a ground vibration of 5mm/s, which is well below that causing damage but some people will complain. A hospital should be at least 500m away from a 100kg charge so that the ground vibration should be less than 2mm/s.

Diagram 10b: Estimating vibration levels for a 100kg MIC shot

Similarly, if you knew that a neighbour’s house was 400m away, you could design your blasting to fire no more than 150kg MIC. If you design shots at 150kg MIC you are unlikely to go past your likely restriction of 5mm/s Peak Particle Velocity.

Diagram 10c: Designing a shot knowing distance to neighbours

4.2.5 COnCussIOn FROm undeRwATeR BlAsTInG

Water is only going to be a problem for you if you are shotfiring directly under water, and then only if the strata is waterlogged. Water is a relatively incompressible substance with good energy conducting properties. Concussion underwater is similar to noise in air. The


energy from blasting radiates away from the blast site as a pressure wave until the energy is lost. Water is such a good conductor that confined and unconfined explosive charges may sympathetically detonate if precautions are not taken. It is usual practice to initiate unconfined charges instantaneously underwater. Unconfined charges would also include shotholes that have no solid stemming, or where stemming is simply water.

Blasting poses a more serous problem to water life, and people swimming, snorkelling or diving in close proximity. If the pressure wave front is of sufficient intensity, it may fatally or seriously injure fish and humans by rupturing blood vessels, affecting lungs and other vital organs. Internal haemorrhage is associated with such injuries.

As a general rule, no blast should be initiated underwater unless everyone is out of the water and preferably on land. To encourage compliance with evacuation requirements, signpost the foreshores about the blast area with appropriate warning signs. Engage additional assistance on shore, and in suitable water craft, to move people to safety and to patrol the water until the blast is over and it is safe for swimmers to return.

Legislation requires that no person should be in the water in the vicinity of a blast. Before conducting any blasting underwater in NSW, contact WorkCover, the Maritime Authority and DPI / Fisheries to determine their involvement and any applicable requirements.

Important

Don’t blast until you are absolutely sure that there are no persons submerged or swimming in water about the blast area.

4.3 IMPROVINg COMMUNITY AWARENESSMost people in the community have no knowledge of explosives yet they’ve all seen the movies and believe the myths and legends about its use. Most would be ready to believe the shotfirer is a ‘cowboy’ without any regard for their property let alone their comfort. The community is becoming more environmentally conscious of disturbance, particularly from blasting, and more vocal in opposing

blast impacts. Blasting presents an element of surprise, because it produces sharp and unfamiliar concussion and noise, ground vibration, dust and sometimes flyrock. Where comfort is disturbed or damage occurs to buildings and structures, people will complain. Depending on the extent of disturbance or damage, they will consider legal action if a satisfactory solution is not found to their initial complaint.

Any complaint or proposed legal action by a neighbour does nothing for the shotfirer/explosives user involved in the dispute, nor for the industry. You might become involved in either a time-consuming legal battle or negotiation process to settle the problem. Sometimes the neighbour(s) is/are unreasonable because they do not want any blasting in the area. Some oppose blasting because they have heard of incidents where damage was caused by unscrupulous users of explosives and are unaware of controls that are being implemented or environmental requirements imposed by the government.

Whatever the approach by the neighbour(s), you must find the patience to explain in some detail:

a. blast locations and future progress

b. blasting times and frequency such as days per week

c. the period of blasting (say, 10 January to 4 May)

d. the purpose for blasting and the benefit it brings to the community

e. relevant environmental factors and controlling mechanisms, including monitoring and adjustment

f. any conditions and disturbance limits imposed by relevant statutory authorities

g. public relations program and methods of notifying persons of an impending blast

h. the need for feedback from neighbours about the level of disturbance.

The degree of public involvement will depend on the sensitivity of the area. You should make every effort to get on with the neighbours, provided their demands are not unreasonable. Further, an open-door policy may be appropriate, where neighbours are able to meet the shotfirer, to see a blast, and examine blast monitoring records at the main office during business hours. Some operations have prepared a written statement that summarises an agreed position with neighbours, and sets out a procedure to minimise discomfort to residents. Keep the format of this document simple and mention the interested parties, as shown in Diagram 11. In


order to obtain their cooperation, distribute a copy of the blasting agreement to all neighbours in the area, even to

those not involved or complaining. An agreement would probably take several meetings to discuss and prepare. This approach is all the more necessary with long-term blasting operations.

Site name:

Address:

Parties involved:

Local Council:

Department of Primary Industries:

Residents of the area:

Site management:

Subject: Blasting

Following discussions with residents and other interested parties, the following procedures have been put in place for safety purposes and to minimise the inconvenience to immediate residents in the areas about the (insert name of your) site.

Scheduled blasting will take place only 4 days per week, namely, Monday, Tuesday, Wednesday and Thursday.

Blasting will take place from 3.30 pm to 4.30 pm only.

Prior to blasting, a horn will be sounded once and 30 seconds later a second warning sound will be issued, followed by the initiation of the blast.

Immediately after the blast and when it is determined safe, the horn will be sounded three consecutive times, indicating ALL CLEAR and the end of blasting activities for the day.

If a misfire occurs, the immediate neighbours will be informed by telephone if another blast is necessary to make the area safe.

During blasting operations:

– the front gate of the site will be locked to people and traffic– (where appropriate) the blast area will be covered with blasting mats to prevent flyrock– all other activities on the site will stop, and available employees posted in strategic areas for personnel security reasons. In the unlikely event that a blast is required outside the agreed times, neighbours will be contacted by site personnel two hours in advance by telephone or in person.

Management of the site wish to establish a good relationship with the neighbours and thanks them for their cooperation. Any feedback or comment should be referred to the manager.

Signed: Site Operation owners

Date:

Diagram 11: Sample of blasting agreement with neighbours


For short-term blasting operations, where blasting is to be conducted in the vicinity of a building that may be the subject of a complaint:

a. Carry out a detailed inspection of the building and if permission is granted, take photographs before and after the blast.

b. Hold discussions with residents to outline the proposed operation and detail precautions taken.

c. Give adequate warnings of firing, both by word and siren.

d. If misfires occur, advise residents of the delay and if another blast will be required.

LEARNINg & ASSESSMENT TASK 4.4 – ENVIRONMENTAL MONITORINg

Assessment


From your previous Assessment Task (4.3), in which you calculated the MIC for two blasts, estimate the ground vibration using the graph from AS2187.2 Appendix J.

Enquire of your supervisor / manager and find out how close the nearest residence is to your blasting activities.

Find out what if any environmental restrictions have been placed on blasting at your site, and compare your estimate of ground vibration with those restrictions or limits.

Enquire of others on site who are involved with blast design to find out what environmental issues are of greatest concern, and whether there have been any complaints about blasting. If there any complaints briefly outline the nature of the complaint and the outcome of any investigation or regulatory response as a consequence.


05REDUCE BLAST IMPACTS

5.1 CONTROLLINg VARIABLESYou must manage, control and limit any disturbance that may injure or cause discomfort to persons or damage to property. In blasting, there are controllable and uncontrollable variables. Generally speaking, uncontrollable variables would include the location of a blast because that is where the work is required—while the direction and orientation of the blast is often controllable, and can be changed to minimise impact on the environment. Some uncontrollable variables would include:

1. the geology of the area

2. the nature and structure of the material to be blasted

3. weather conditions

4. groundwater

5. adjacent land use and encroachment of housing nearer to the site.

These variables are beyond the control of the shotfirer, but still need to be considered.

Controllable variables are generally the specifications of the blast, which you can alter to obtain a balance between required product, safety and environmental acceptability. Other controllable variables are:

1. hole diameter

2. depth

3. hole length and inclination

4. the length and type of stemming

5. bench height

6. shothole pattern

7. initiation method

8. delay sequence

9. free-face arrangement

10. perimeter blasting need

11. explosive type

12. charging arrangement

13. powder factors

14. time of blasting

15. frequency of blasting per week.


By managing the controllable variables, and making allowances for the uncontrollable variables, satisfactory results can be achieved, but this sometimes is not an easy task.

5.2 REDUCINg FLYROCK RISK Every shotfirer/explosives user has a legal duty to control flyrock from any blast. The major parameters associated with controlling flyrock from a quarry blast are:

1. charge configuration

2. shothole location

3. stemming medium

4. initiation point and sequence

5. blast pattern shape and alignment

6. protective cover

7. powder factor.

Flyrock possibilities must always be at the forefront of your mind. You might find a checklist useful (see Diagram 12) especially if you are blasting in a new location.

5.2.1 usInG A FlYROCk PRevenTIOn CHeCklIsT

Question Response

What is the ground like?

Are there any faults, fissures, floaters, caverns?

Is the jointing pattern in the rock angled in such a way that rocks will come out easily in a particular direction?

Has the drilling been executed as planned?

What is the front row like in particular (check the burden on every hole)?

Has any ground fallen away since the drilling was completed?

Is this a tight blast?

Are there any tight spots where the ground will have difficulty in moving?

Has the loose material been mucked out in front of the face?

Is the drilling accurate, particularly in the toe area?

Is my stemming material and depth adequate?

Will my initiation sequence work?

Is the delay adequate?

Is the blast aimed at any place where people (or animals) could be?

How far do rocks normally fly in this direction?

Is it still safe for people beyond the quarry boundary?

Have I changed my explosives?

Have I changed the blast design or size?

Have I changed the initiation sequence, stemming or anything else since the last blast of this type?

Has the ground changed, or the direction of the blast?

Should I reduce the size of this blast, just to be sure?

Have extra cartridges been placed in the bottom of the hole to overcome the water table, hence increasing the powder factor?

Any other comments.

Diagram 12: Flyrock prevention checklist

Where flyrock potential may be enhanced by the jointing pattern of the rock, you might adjust the face orientation or the initiation sequence in order to avoid sending flyrock in a particular direction.

5.2.2 usInG BlAsTInG mATs

Use blasting mats where flyrock may be a potential threat to people or property, in close proximity to occupied buildings, structures or public areas, if you are shotfiring at or near the surface. Blasting mats are heavily woven mats, of robust materials, such as rope or steel wire. They are placed over the charged holes just before firing to contain the blast and prevent flyrock. It is wise to protect the mats from excessive damage by placing logs or railway sleepers over the blast area, and then positioning the blasting mats on top. Protect the mat from the cutting action of any exposed initiating explosives. A


common cause of fly material when blast mats are used is the failure to secure down their sides and ends. Charges on the first delay lift the mat, and, while it is suspended above the remainder of the shots, the fly projects from under the mat.

Where earth-moving machinery is available and heavy blasting mats can be shifted with ease, you could use steel cover plates of 10-15 millimetres thickness as a blasting mat. Frequently, concrete blocks of several tonnes weight are placed on top of the steel plates to weigh them down - as a flying steel plate can be just as dangerous as a flying rock. When steel cover-plates are used, take care to avoid contact with electrical terminals in the firing circuit, as it may cause short-circuiting. Also take care not to cut a connecting line when positioning the cover plates.

Heavy-duty industrial blasting mats, specially constructed from strips of rubber tyres, are now commercially available. These have the advantage of negligible water or dust absorption and are easily handled by two people. Improvised blasting mats made from timber, logs, car tyres, brushwood, and fencing or chicken wire have been successfully used. This sort of cover is of particular use to the shotfirer/explosives user who cannot employ heavy moving equipment. It has the added advantage of being porous, allowing the expanding gases from an explosion to pass through, but trapping the projected rocks. If available, overburden or soil (free of rock) has been successfully used to cover a blast to prevent fly material.

5.3 REDUCINg DUSTDust can be reduced by:

1. selecting an acceptable powder factor

2. reducing the height of blasted material

3. watering down all exposed surfaces to be affected by the blast to minimise the disturbance of already settled dust

4. using good stemming to avoid ‘blow-outs’ and avoid using drill cuttings.

The dust from the impact of falling broken material on the quarry floor is a major cause of dust. The powder factor needs to be examined to ensure that optimum fragmentation, and minimum movement, is achieved. Where possible, if the area is dry or is layered with dust from loading-out operations just completed, water the area where material is to fall, by the water cart.

Poor stemming is also a contributor to dust, particularly where drill cuttings that consist mainly of dust are used. It is also during the detonation process that stemming is ejected, so the finer the stemming, the more likely the ejection and formation of dust. Fine-crushed, screened stone may be used as stemming, or quick-setting cements and jellied water solutions are used to minimise dust from stemming ejection – just make sure it is not from reactive ground!

Coal may be a particularly offensive dust in some communities - especially those who have been passionately opposed to the site - mainly because of its colour and the fact that it can remain suspended in air due to its low density, so it travels greater distances and is seen by more people.

5.4 REDUCINg ‘NOISE’, OR AIRBLAST OVERPRESSURE Reduce the effects of noise from blasting or airblast overpressure by:

1. recognising weather conditions which influence sound travel

2. recognising favourable and unfavourable weather conditions

3. restricting blasting operations to favourable days

4. restrict blasting to favourable times.


Favourable atmospheric conditions for blasting are clear, to partly cloudy skies with fleecy clouds, light winds and a steadily increasing surface air temperature from daybreak to blast time. Unfavourable atmospheric conditions for blasting are:

1. foggy, humid, hazy, or smoky days with little or no wind

2. conditions typical of temperature inversion and high air-pollution index

3. during strong winds accompanying passage of a cold front

4. during periods of the day when surface temperature is falling.

Temperature inversion with low-lying clouds amplifies blast noise-levels, and sometimes people who are some kilometres away will complain. Temperature inversion is an atmospheric condition where a layer of dense cold air is trapped between the earth’s surface and an upper layer of less dense warm air.

Smoke rising from a chimney, flattening out horizontally after the initial rise, is a good indicator that a temperature inversion is present. Contacting the local airport for a weather report is another way of determining a temperature inversion. Where these effects are critical, some operators have adopted the practice of not firing if the wind velocity towards residences exceeds 20 km/hour. Blast time should be delayed to mid-morning to allow early morning temperature inversion, if any, to be eliminated.

To minimise neighbours’ complaints, a good rule is to select a firing time that takes into account the activities of the neighbourhood. The right time for your site may be 12.30 pm, when you know everybody is out to lunch; or 3.15 pm when everybody is on the move, at work, or travelling home; a majority of mothers also collect children from school or kindergarten at that time.

To verify that noise is not an offensive component of blasting, you might engage the services of a noise consultant or conduct a model blast using a sound-level meter (measuring in decibels on the Linear Scale) to monitor the actual noise level at a complainant’s premises.

Important

Reduce noise by covering exposed explosives.

Minimise explosives detonating in the open air, either by design or accident through overcharging. Also:

1. Use delay-blasting techniques to reduce the maximum instantaneous charge.

2. Select and use good-quality stemming.

3. Use adequate length of stemming.

4. Use initiation systems other than detonating cord.

5. Cover surface detonating cord with 200–300 mm of soil or crushed rock.

6. Eliminate secondary blasting by improving fragmentation of primary blasting, and use mechanical methods to fracture boulders.

7. Where secondary blasting is unavoidable, use popping charges instead of plaster charges.

8. Avoid the use of unconfined explosives, regardless of purpose.

9. Ensure the blast proceeds in the proper sequence.

10. Consider geological anomalies and ground conditions.

11. Use non-explosive decks through mud and dirt seams to prevent blow-out.

12. Make sure drillers report any solution cavities in limestone that could be overloaded with bulk explosives.

13. Schedule the blast at times when neighbours are normally busy or expect blasting to occur.

14. Avoid early mornings or late afternoons, to reduce the possibility of blasting during temperature inversions.

15. Identify favourable and unfavourable weather conditions in advance.

16. Avoid excessive delays between holes to prevent unburdening holes.


5.5 MINIMISINg gROUND VIBRATION1. Use a blast that is designed to give

the maximum relief practical.

2. Select and use the proper powder factor to achieve the desired result.

3. Use a spacing-to-burden ratio equal to or greater than one, if possible. The presence of weak seams, or irregular back break, may dictate the use of a spacing to burden ratio less than one.

4. Control drilling of shotholes as closely as possible to prevent reduction in hole deviation, and ensure the uniform distribution of blast energy.

5. Keep subgrade to an absolute minimum.

6. If hole depth is more than the intended amount, backfill with drill cuttings or crushed stone.

7. Use various techniques to reduce the maximum instantaneous charge and, in turn, the peak particle velocity.

8. Lower bench heights.

9. Use smaller-diameter holes.

10. Use deck-loading techniques with different delay periods between decks.

11. Eliminate sympathetic detonation by using less sensitive explosives.

12. Use delays to reduce the number of holes on a delay period - for example, when excessive vibration is caused by 200 pre-splitting shots, divide the pre-split into four groups of 50 shotholes.

Reference

AS 2187.2 summarises the most significant procedures that can be used to control ground vibration.

An extremely valuable assessment technique (which can be used as well for blast record purposes if complaints are likely or difficult conditions exist) is to photograph, film or video a blast so as to see the progress of dust emission, stemming ejection, and ground throw. It is often surprising how much information you can derive from even basic photography.

A blast that is designed to minimise ground vibration to acceptable levels, which is stemmed well and where ‘blow-outs’ are unlikely, is also unlikely to produce unacceptable airblast (noise) levels. The intensity of ground vibration originating from blasting is measured as peak particle velocity (mm/s), and limits are expressed in this way. Peak particle velocity can be estimated by using a formula or ground vibration tables (see precious chapter).

LEARNINg & ASSESSMENT TASK 4.5 – BLAST IMPACT REDUCTION

Assessment


From your previous Learning & Assessment Task (4.4), in which you found out what if any environmental restrictions are been placed on blasting at your site, and you found out what environmental issues are of greatest concern at your site, outline how you measure or monitor these issues. What instruments are used and what readings are taken. When do you turn the instruments on. If your site does not take routine measurements of environmental issues, find out from your supervisor or blasting expert or manager how your site has estimated the environmental impacts and whether this was based on external expertise with or without trial blasts or occasional measurements being taken.

Also outline the controls for typical blasts at your site in relation to these issues.

In particular, outline also your site approach to minimising any risk of flyrock.


06DISPOSE OF DETERIORATED, ABANDONED OR DEFECTIVE EXPLOSIVES

Module 1 addressed the detection of deteriorated explosives. In that Module the simple statement was made not to use deteriorated explosives. They must be got rid of, and an experienced person must supervise the task; an experienced person understands the risk of detonation during disposal, and the necessary controls for that risk.

Important

Always assume that explosives will detonate during disposal

They may be burned or disposed of in a bulk process. Massive amounts are, infrequently, taken to a place like Woomera and detonated.

If the deterioration or defect has arisen on site it is vital that the conditions under which that occurred is corrected, so a report to senior operational staff is vital before any action is taken. The site may want to involve the supplier and/or manufacturer. Sites may have requirements for disposal so check any procedures first.

6.1 COLLECTINg & REMOVINg EXPLOSIVESAt some time during your career, you will be required to remove or dispose of damaged, surplus or defective explosives from licensed magazines or industrial or (especially old rural) domestic premises.

1. Preventing injury and damage to property are the two most pressing considerations. Check any site procedures for requirements.

2. Notify any site emergency personnel that disposal is taking place and give them relevant details of quantity, location and possible risks

3. Guard and/or signpost the area to prevent and restrict entry of unauthorised persons while you are organising the collection of the explosives.

4. Visually inspect the immediate area where the detonators or explosives are situated, and develop a safe removal plan.


5. Clear the immediate area of potential falling objects, rubbish, flammable, combustible or volatile liquids.

6. Clear a path for entry and exit purposes.

7. Switch off electricity or gas if considered a risk.

8. Depending on the condition and quantity of explosives or detonators, seek the assistance of emergency services and have the area evacuated if necessary.

9. Inspect the area for spiders or other insects that may cause distraction during the removal of explosives.

10. Using a good carton, transfer the explosives or detonators carefully from their current position—do not be rough, but be definite.

11. Inspect cartridges to ensure there are no detonators.

12. Do not stress a detonator if it refuses to come out of the cartridge.

13. Remove explosives and detonators separately.

14. Using another good carton, remove the box, plastic bag or packaging separately.

15. If necessary, or you have any doubt about the explosive ingredients soaking into the shelving, remove the shelving for burning as well.

16. Inspect area for other loose explosives.

17. Move defective explosives to open space until ready for transport.

18. Depending on the condition of the defective product, transport the minimum distance to a safe disposal site.

19. Sawdust or similar material should be used to absorb any liquid if nitroglycerine is found as a free liquid in the carton, or spread on the surface of the floor. If it is found as a liquid or it is likely to have exuded in the past, the affected area should be treated with a copious quantity of nitroglycerine-destroying liquid (see Appendix 3) and allowed to stand for several hours. When the reaction is complete the saturated sawdust may be removed and the residue washed with water. The saturated sawdust must be treated cautiously; if it is to be disposed of by burning it must be treated in the same manner as a highly flammable liquid and burnt in an open area.

Important

Where there are defective explosives, there is a high probability that there may be defective detonators also, and vice versa.

6.2 DESTROYINg EXPLOSIVES AND DETONATORSSurplus or defective explosives should never be placed in any lake, creek, river or dam, thrown away, abandoned or placed with rubbish. AS 2l87.2 also provides information on the destruction of explosives, and this Standard commonly forms the legislative basis for handling the destruction of explosives on a mine and quarry. As a general guide, explosives can be destroyed as summarised in Diagram 13.

explosive product destruction by

Detonation Burning Water

Black powder • •

nitroglycerine • •

AnFO • •

watergels • •

emulsions •

Cast primers • •

detonating cord • •

detonators • •

detonating devices • •

Diagram 13: Destruction of defective explosives and detonators

A larger amount of fuel is often required when burning slurry and emulsion explosives and cartridges should be slashed to allow vapours to escape as well as to reduce the risk of detonation due to heat build-up. Cartridges should not be placed on top of each other; this also reduces the risk of detonation due to heat build-up in layered explosives.


6.3 COMPLYINg WITH LEgAL CONSIDERATIONSLegally, the person intending to collect and destroy defective explosives must:

1. contact the appropriate authority / government agency

2. be trained in the destruction of explosives and be qualified users of explosives (in NSW you must hold a BEUL to destroy explosives)

3. be responsible for the safety of persons and protection of property

4. only use methods prescribed under legislation.

It is important for authorities to be informed about what has caused the defect and whether this might impact on the approval, storage, handling, transport or use of this explosive or others like it. Authorities welcome advice about problems you have encountered so they may inform others to be on the look-out, as well as to make sure the suppliers/manufacturers make the necessary improvements.

LEARNINg & ASSESSMENT TASK 4.6 DISPOSAL OF DETERIORATED EXPLOSIVES – SAFE OPERATINg OR WORK PROCEDURES

Assessment

Go to your Learners Workbook 4 and complete Learning & Assessment Task 4.6 by investigating your site’s procedure for disposing of defective, deteriorated or obsolete explosives. If your site does not have a procedure, prepare one specifically developed for your site. You should refer to:

1. provisions in magazines (if you have them on your site) for holding explosives awaiting destruction;

2. processes for destroying small quantities of explosives;

3. on-site approvals for destroying larger quantities of explosives;

4. notification to government agencies;

5. specific places for destroying explosives;

6. warnings and supporting personnel requirements;

7. guarding entry during burning and site clearances;

8. reporting / recording of destruction activities and stock records.


07MAINTAIN DOCUMENTATION & REPORT

7.1 TAKINg A SYSTEMATIC APPROACH TO THE MANAgEMENT OF EXPLOSIVES USAgE AND RISKSIn all Modules there has been some discussion about reporting of various kinds. In this Module the focus of reporting should be to keep improving explosive use and the main document will be the blast plan records. These records also prove invaluable if there is a complaint about the blasting or a security scare. Every organisation needs a shared commitment for completing work in the safest possible manner. With the enactment of common occupational health & safety legislation, the principle of ‘due diligence and care’ was introduced. It has placed a far greater onus on employers, employees and other persons to work in such a manner that the health and safety of any person was not at risk.

Under current legislation and (in simple terms):

• Everyemployerisrequiredtominimiserisktohealth and safety by making the workplace safe, providing adequate and appropriate training, and providing suitable equipment to complete the work.

• Anemployeeisrequiredtousetheequipmentsupplied safely, wear and care for safety equipment provided, and work in a safe manner with others.

• Anexplosivessupplierisrequiredtomanufactureproducts that can be handled safely, to provide all relevant data on product use, performance, safety, first aid and hazards and to provide training.

• Everyoneshouldsupporttheorganisation’ssystematicapproach and seek to improve their work procedures.

Supporting the site’s systematic management of risks associated with explosives is also vital. Each site will have some documents in relation to explosive usage. These must be referred to and upgraded based on experience on site or others’ experiences as informed to you by safety alerts or by your own enquiries.

Important

Complaints, which are left unaddressed, may result in costly legal proceedings or delay the job.


Appendix 2 contains an abstract from AS2187.2 regarding Blast Management Plans, which are effectively mandatory. These 4 modules have progressively developed your skill and knowledge to conform with these management plans.

7.2 BEINg ACCOUNTABLE & RESPONSIBLE FOR RECORDSEveryone who has unsupervised access to explosives is accountable for maintenance of records. Explosives users must keep legible, accurate, up-to-date records and statistics for their own sake. They must also be readily available in response to a complaint, and for inspection by the authorities. The keeping of good records is good business, good management (especially if explosives or detonators are unlawfully taken from your magazine, or neighbours allege excessive blasting exceeding environmental limits) and good for blasting crew purposes to support communication.

Important

Treat your blasting records in the same manner as your taxation information.

Statutory documents indicate that a person, or business, is authorised to conduct certain blasting activities, or to hold explosives on a premise.

7.3 gIVINg COMMITMENT TO YOUR SAFETY POLICY Employers have safety policies to raise the level of safety awareness, to encourage an improvement in safety levels, and to provide the basis for on-going improvement. The best policies are often the simplest, because they are easiest to communicate. An example or outline of a safety policy is given in Diagram .., and reflects a common approach to having a one-page policy, but most organisations personalise their policies.


sITe sAFeTY POlICY

AIm: The aim of this program is to develop a health and safety policy that will guide management and employees in the planning, development and implementation of our safety management plan (SMP).

wHAT: This policy is the basis of our SMP and looks at what we believe are our main health and safety goals. To be safe & healthy our site aims to develop a strong safety culture in which blame or shirking responsibility don’t have any place. Our equipment is to be user-friendly, and fit-for-purpose at all times, so we practise preventative maintenance. People who work at our site need to fit right in, are suited to the tasks we undertake, and are competent and committed to our policy. We have procedures for undertaking critical tasks in a safe & healthy manner that are kept up to date.

OH&S Policy: Goals for the coming year

Management Date

Employee Representative Date

wHO: This policy has been developed and reviewed jointly by management and employees. Both management and employees have signed off on this policy document displaying commitment and ownership.

HOw: At site safety meetings, management and employees will be involved in refining the goals of our policy. The policy is to be reviewed on __________________ at a joint meeting of management and employees.

wHen: Each year, at the site safety meeting we intend to use FORM xx to record our safety targets for the year. We will review this at the end of each year to see if we have achieved our target. We will modify our following year’s targets to account for any shortcomings.

ACTIOn: The yearly safety plan (FORM xx) is to be completed by ____________________ .

dOCumenT COnTROl: A copy of this policy is to be displayed in the ______________________

with the master showing the last review date remaining in the SMP.

Diagram 14: Example of a safety policy


It does not have to be anything fancy, but the message must be conveyed to everyone from the beginning of their employment, and then continually reinforced at work. When writing a safety policy, consider the risk management advice and safety rules given in the previous units.

7.3.1 BlAsT mAnAGemenT PlAn

A safety management plan for shotfiring and explosives should be put together. In some case, such as in NSW it is a legal requirement under coal mine safety legislation to have a major hazard management plan for explosives.

AS2187 also makes it an obligation to have a blast management plan because Appendix A of this Standard is “normative’, which means mandatory, and any legal case will view failure to observe this Standard very dimly. Appendix 2 in this manual contains an extract for your convenience on this very important topic.

When you think about it, a blast management plan is logical and is not just paperwork. It starts with the safety policy and progresses through risk management, procedures that are required to support risk controls, training in procedures, ‘tickets’ to confirm an individual’s training plus experience, instructions in relation to specific blasting, which should be recorded individually, supervision to ensure instructions are being observed, checks by the organisation as well as by the individual, and these might suggest maintenance is required. All of this requires some records, and is kept up to date so there needs to be established early on a system of document control.

7.4 KEEPINg RISK MANAgEMENT RECORDSRisk management is an integral component of a safety management plan. It must be a process to foresee risks and put controls in place. Controls include eliminating the risk by not doing some things or substituting a high risk for a much lower risk, or engineering out the risk by putting physical barriers in place to prevent someone coming into contact with the hazard, or minimising the

exposure to the risk, or putting softer controls such as training, procedures, supervision and Personal Protective Equipment (PPE) into place. Risks must be monitored and emergency responses prepared.

People must be involved in decisions about risk acceptability and the controls that are put in place. They must also know about the monitoring and emergency responses. However, not all risks can be foreseen so it is important that people understand when and how to undertake a risk assessment. They must understand which type of risk assessment is appropriate under different circumstances.

Risk assessments are a necessary part of managing risks when something changes or has not been foreseen by the site. Sometimes this will involve only one significant change, such as a significant change in location for blasting or a significant change in the task. If one thing changes conduct an informal risk assessment such as a ‘Take 5’, ‘SLAM’, ‘STOP’, ‘TRACK’ that many larger organisations have for such an event. Do this informal risk assessment with another person involved in the task so you have the benefit of another set of eyes looking out for hazards. However, if two significant things change conduct a more formal risk assessment / JSA and involve the whole team. Keep a record of the risk assessment because using explosives is a high-risk activity.

7.5 DOCUMENTINg PROCEDURES Safe working procedures or standard operating procedures are commonly prepared for major risks/tasks and kept in a place where they are readily accessible. These will be updated as the need arises, and should be reviewed as a matter of course on a regular basis, especially involving those who have been exposed to the risks for which they were prepared. Procedures are necessary for safe and efficient operations, and they are vital to help retain ‘corporate knowledge’, to communicate expectations and to make on-going improvements.


7.6 TRAININg & RECORDSTraining, education, knowledge and experience are four factors that commonly contribute to the safe use of explosives. Training in the use of explosives is available from various sources to help people understand the risks they face, the precautions to be taken, and monitoring improvement processes. In particular, people must have structured training in procedures to boost their knowledge and experience. Training records must be maintained.

7.7 SUPERVISINg & MAINTAININg SHIFT RECORDS Supervision is a vital part of making sure that necessary precautions are being taken, that any new hazards are being identified and risk controls upgraded, that everyone is meeting expectations, as well as to coordinate actions across the site. Brief notes that record special events or conditions during the shift should be maintained and used in shift handover discussions as well as in later communications, such as in production and safety meetings.

7.8 MAINTAININg SITE SECURITY, INDUCTION & ACCESSAll people who come on site should register their presence. This is vital for emergency responses, but it also provides an opportunity for inducting people to the risks they may face on site and the expectations placed on them under certain circumstances.

Contractors & suppliers

Contractors (including sub-contractors), in particular, need inductions – both generic to the site and task-specific in relation to their particular task and location. All sites need to anticipate engaging contractors and have basic processes and procedures in place to avoid unwanted delays in continuation of operations, as well as to record their activities and the outcome of their work. There will be various records kept in relation to contractors.

In particular, contractors must submit copies of workers’ compensation, public liability and where applicable, professional indemnity insurances.

Contractors will also have to supply copies of:

1. all relevant licences,

2. procedures, and

3. Safe Work Method Statements (SWMS).

Where appropriate, contractors may need to make generic risk assessments and SWMS relevant to particular site needs. Contractors will have their own ‘safe systems of work’ and may need to liaise with sites regarding improvements to their own or to the site’s system.

7.9 MAINTAININg EqUIPMENT AND FACILITIES As with all equipment and facilities (such as magazines, vehicles and blasting machines/exploders) used on site, maintenance is a vital part of safe and efficient blasting. Maintenance also includes calibration of mobile mixing units. Maintenance records are required.


7.10 MONITORINg SAFETY & HEALTH, PRODUCTION, ENVIRONMENT AND COMMUNITY RELATIONS PERFORMANCEBlast records provide the central means of monitoring blasting practices, in the same way that magazine records monitor stock usage. Blast records should contain environmental monitoring results. A summary of all these records should be taken to regular safety meetings, which are the forum for monitoring all site activities, and deciding what has been done really well and what needs improvement.

7.10.1 usInG dIARIes

A shotfirer who maintains good stock and blast plan records may not need to maintain a diary, providing that the blast records contain information regarding any concern. However, anyone who is involved with explosives and who is responsible for the safety of others should get into the habit of keeping a diary or ensuring that all concerns are included in the blast plan records. Diaries are particularly valuable as a reminder of things to do, going forward, unlike stock and blast records that track the past even where they help as a future reference.

7.10.2 COmPlYInG wITH, OR enFORCInG Rules And sTAndARds

Explosives are not kind to those who ignore common requirements. Legislation is one way of passing on the hard-won experience of others. Legislation might not make easy reading, but if incorporated into the workplace and in the field, through observing the rules of safe operations, it can become a useful tool. It is important to make the rules freely available, to apply them at work, to correct co-workers when errors are noticed, and to notify regulators of your hard-won experience. The onus on every employer is not only to advertise and promote safety rules, but to enforce them as well. Enforcing the policy is probably the most difficult part to achieve. It means that a qualified supervisor must be present to observe practices, give directions to complete work and meet blasting timetables. Ignorance is not a defence in the eyes of the

law, so users of explosives must become familiar with legislation and standards. Without being too dramatic, a shotfirer has the lives of others in their hands, so they must make sure that standards are being observed.

Each member of every blast crew must do the same things as the others in their crew – every time. If there is a concern it must be discussed openly with all members of the blast crew and the concern properly resolved – as has already been said, explosives may not give you a second chance – sometimes by reference to legislation and sometimes to another body of knowledge. If the resolution of the concern is to make a change, everyone must be committed to it.

A diary may have to record disciplinary action, and this may have to escalate to other levels if the behaviour is not improved – for the good of all concerned!

7.10.3 mAnAGInG RIsks – RIsk ReCORds

There are several types of documents relating to hazards and risk management, and these might be seen as a progression, commencing with a hazard report. There are, of course, similar reports for equipment, starting with a pre-start check, but the following discussion focuses on safety in general, given the high-risk nature of shotfiring; the hazard might not be all that likely, but the consequences are often significant.

Hazard reporting

Hazard reports contain basic information in relation to concerns. A typical hazard report is illustrated in Diagrams 15a, b.


Diagram 15a: Hazard reporting process outline (NSW DPI & IQA)

Diagram 15b: Typical hazard report form (front) (NSW DPI & IQA)

These reports simply identify concerns, and are particularly valuable where the person who identifies the hazard does not have the capacity to fix the problem. These forms/reports complement workplace inspection reports, where the primary aim is to identify new hazards and see how well previously identified hazards are being controlled.

Informal risk assessments

If the person has a concern over which they have some control they might fill in an informal risk assessment. These are particularly valuable when you:

1. change work location – such as when you change from a normal blasting situation in the pit, to do shotfiring at another site. This could also apply for an underground shotfirer going to do a surface shot; or when you

2. change tasks – such as when you change from a standard shot to do a pre-split.

An informal risk assessment has many shapes and names. A typical one is a ‘Take 5’ as shown in Diagram 16.


Diagram 16: Typical ‘Take 5’ form

An informal risk assessment is best done with two or more people, and completed on the job, looking at the general working environment, the equipment and materials being used, the people involved and the procedure to be followed. The NSW DPI publishes a ‘Risk Management Pocket Guide’ that comprises a hazard report pad, as well as an informal risk assessment pad. It also contains a series of pocket cards to support hazard identification. The ‘Pocket Guide’ booklet (as opposed to the pocket book) contains sample forms of formal risk assessments and Safe Work Method Statements; see http://www.dpi.nsw.gov.au/minerals/safety/publications/workbooks .

Formal risk assessment

When both the work location and the task changes, it is best to do a formal risk assessment involving the whole team and not starting work until it has been reviewed by a supervisor. A commonly preferred way to do this is to do a Job Safety Analysis (JSA, sometimes called a Job Hazard Analysis or a Job Safety & Environment Analysis). A JSA (or its variation) gets you to list the steps involved in the task then do a risk assessment of all steps from set-up through to putting the gear away and making sure it is ok for the next time; otherwise you may simply do a ‘brain dump’ of hazards and miss something important. Many people who are about to do a task that they don’t do all the time, head straight for a JSA rather than a procedure, which is often more detailed. A typical formal risk assessment is shown in Diagram 17.


Safe Work Method Statement

A formal risk assessment can lead on to a Safe Work Method Statement (SWMS), which is an outline of the task that is based on a risk assessment and also involves special consideration of key features of:

1. the managed working environment

2. equipment and materials

3. people, and

4. procedures.

This is a common progression for contractors, where the site engages in the special consideration, by way of a double check. A double check by someone with fresh eyes is always wise, so a SWMS is also a feature at some sites where blasting is regarded (wisely) as a high-risk activity. A typical SWMS is shown in Diagram 18.

Because shotfiring can be a regular task, and because a SWMS is an outline, it is common for procedures to be drawn up. Procedures are sometimes called Safe Work Instructions (SWI), Safe Work Procedures (SWP), or Standard Operating Procedures (SOP). The name change might reflect site documentation or legislation, but they are essentially the same. They capture corporate memory in a more explanatory way than in a JSA or a SWMS. They also have key features like definitions, responsibilities and document control that supports third party auditing.

Training manuals

Often after hard-won experience, procedures are amplified with fine detail and pictures. There comes a stage when these are more valuable as a training manual than for everyday reading.

Systems and Contractor documentation

There are a number of other documents that could be described. In the case of contracted work, a Contractor Safety guide has been published by the NSW Minerals Council at http://www.nswmin.com.au/news,_reports,_submissions/publications .

Feedback, including ‘Toolbox Talks’

Feedback is an essential component of managing risks. When someone has taken the trouble to fill in a hazard report form, risk assessment, SWMS, or reviewed a procedure, you must consolidate that input by giving feedback. Common steps in giving feedback include:

1. what happened – what was the thing that prompted/triggered action (eg “Bill identified a hazard with our disposal of unwanted primers in yesterday’s shot, with some primers getting stuck down the shothole when we simply dropped them down”)

2. what was the reaction – what was the response to the thing that triggered the action (eg “We then had trouble dislodging the primers and had to try and pump emulsion around the primer, with the new primer only part way down the shothole”)

3. what happened as a result of the reaction (eg “So we’ve changed our procedures and will be threading any unwanted primers onto the proper primer so we can lower them both down the shothole under control, and not airmailing unwanted primers out of control”)

4. what will happen next (eg “We’ll make sure everyone involved in charging at any time is made aware of this change”).

Toolbox Talks are a common way of reaching all shifts and of passing on any of this sort of information. They also provide an opportunity for anyone to raise a concern or query, or to discuss any aspect of their task. As a consequence they are often held as a pre-start meeting for any shot. They may also be a way of passing on information from a safety alert. For example, the safety alert that came out from the Queensland Explosives Inspectorate concerning vehicles and signal tube, referred to in Module 1, might have prompted discussion at a toolbox talk/pre-start meeting. Toolbox talks should be recorded – especially recording any action arising from discussion. A typical record form is shown in Diagram 19.


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Diagram 18: Typical SWMS (NSW DPI & IQA)


FORM: TOOLBOX TALK OR PRE-START MEETINg DISCUSSION DETAILS

Date Time: am / pm Shift:

Supervisor / recorded by: Location

Contents of Toolbox Talk or Pre-start meeting

Safety

(cross- reference or topic)

Notices

Other (especially any changes)

Issues Action Responsibility Timing Review required by

sign-off

People Present name Task signature site / contractor

/ visitorPermits, induction, etc requirements

Diagram 19: Typical Toolbox talk or Pre-start meeting record


LEARNINg & ASSESSMENT TASK 4.7 - RECORD-KEEPINg

Assessment

Go to your Learners Workbook 4 “ and complete Learning & Assessment Task 4.7, which is for you to compile a suite of typical records maintained in relation to the use of explosives, including a copy of the site safety policy. This task will require you to track down a variety of records, so don’t get bogged down in detail. Rather you should begin to see the context of the records from two major perspectives:

1. to see records of the four components of work, namely the managed working environment, equipment and materials, people, and processes; and,

2. to see how the continuous improvement loop requires sites to have a clear aim or intent for safe operation, to have a logical approach or plan to achieve that aim, to implement the plan, to monitor the plan’s implementation, and lastly to make on-going improvements based on the facts derived from the monitoring.

On every record you might make a note of your involvement in the record-keeping. For example, you might note “this is a copy of the record I (or our team, or the shotfirer, or my/our supervisor, or the maintenance person, etc) made on (date) following (the blast, activity, concern expressed, etc)”. On another example you might note your review of a procedure/training etc.


gLOSSARY OF TERMS

Reference books on explosives often contain technical terms to help communication. Terms may also be derived from legislation, standards, codes and other sources. Legislation contains specific definitions that may differ from generally accepted definitions. AS 2187.0 Explosives: Glossary of Terms contains terms commonly used by blasting practitioners who follow codes, current word usage, literature and manufacturers’ information. These terms are also used in official documents, courts of law and technical papers.

Acoustic warning

A distinctive audible warning used to indicate the progress of a blasting operation

Acts Developed by statutory authorities, passed by Parliament and become law of the land

Afterdamp Atmospheric pollution following fire or explosion (usually lethal)

Airblast, airblast overpressure

Airborne shock or pressure waves from an explosion, which are mostly at low frequencies that are below the frequencies that we ‘hear’. These terms are used to avoid confusion with ‘noise’, which are sound pressure waves at frequencies that our ears detect

Air deck Uncharged length of blasthole by using airbags

Anfo A common bulk explosive, which is a high explosive mixture of Ammonium Nitrate and Fuel Oil (diesel), with or without approved additives, but not including aluminium

Approved Approved by the appropriate government agency or authority

Auxiliary fan Used in conjunction with air ducting to direct a portion of the main ventilating current to the working face

Back break Ground broken back past its designed shape

Back end Side section of the coal face remaining after the centre section has been shot out by explosive

Back (or bottom-) primed

When the priming charge of a shot is placed at the back or bottom of the blasthole or shothole

Bar down To lever loose material from the roof or backs to make it safe

BCm or Bank Cubic metres

The volume of rock before it is blasted

Blasthole or shothole

A hole which is charged with explosives for blasting purposes


Blasting agent A descriptive term used to denote certain high explosives such as those consisting predominantly of ammonium nitrate and in which none of the ingredients is classed as an explosive.

Blasting area The area near blasting operations in which concussion or flying material can reasonably be expected to cause injury

Blasting cap A detonator containing a charge of detonating compound, which is ignited by electric current or the spark of a fuse. Used for detonating explosives – as opposed to a ‘cap’, which is a piece of timber placed on top of legs for strata support

Blasting circuit Electric circuits used to fire electric detonators or to ignite an igniter cord by means of an electric starter

Blasting explosive

An explosive used in mining, quarrying and excavations generally, and includes cartridges and bulk explosives, and their means of detonation (eg detonators, primers and detonating cord)

Blasting mat A mat made of rope, rubber strips, polyethylene tube or other similar material, placed over a blasting area to prevent debris from being scattered

Blister shooting The breaking of rocks by firing charges placed against them and may be confined by sand-bags, mud or clay. Also known as plastering.

Blown out shot A shot that has failed to do its work; the energy of the explosives has blown out of either the front or the back of the shothole

Booster An explosive, commonly being the same as a priming charge, used generally in small quantities to maintain a high velocity of detonation through the main charge

Borehole pressure

The pressure in a blasthole caused by the high temperature gases from the explosion

Box cut A blast pattern where the rock has no initial free face and movement will be roughly parallel, not at right angles, to blastholes. Needing higher ‘powder factors’ than when rock moves at right angles to blastholes. Similar term to ‘drop cut’

Break A crack or cavity in the strata encountered when boring a blasthole

Break detector A specially shaped tool used to detect breaks in blastholes

Brisance The ability of an explosive to break (or shatter) by shock or impact as distinct from gas pressure

Bulk strength Energy/unit volume of explosive, commonly as compared to the strength of ANFO

Bulled hole A blasthole which has been enlarged (chambered) by exploding a light charge of high explosive in the bottom; a hole with a chamber at the bottom to accommodate a larger quantity of explosive, or an enlarged blasthole resulting from a blown out shot., where the blasthole is or may be shattered to a greater or lesser degree

Bulling A procedure intended to enlarge, by compression from an explosion, a section of a blasthole in order to obtain a greater quantity of explosives at the point - depending on the charge and generally results from a greater “burden” on the shot than would allow it to pull properly

Burden The distance between the charge and the free face, or the distance apart in the direction of ‘heave’, as opposed to ‘spacing’; the thickness or quantity of rock/coal that a single shot or number of shots is expected to move

Burn cut A number of more or less parallel holes drilled into a face, some of which are charged and fired to form the “cut” into which subsequent holes fire

Butt That portion or remainder of a blasthole found in the face after a shot has been fired

Cap- or detonator –sensitivity

A common term, referring to the explosive’s ability to be reliably detonated by a No. 8 strength detonator.

Capped fuse A length of safety fuse with a plain detonator crimped on to one end

Capping station A special place, bench, room or building used expressly for preparing capped fuses, often comprising a holder for a roll of safety fuse and a mark that indicates the desired length of fuse (generally being more than the minimum of 2m)

Cast The same as ‘throw’, the movement of rock forward, and is most commonly used in surface mining

Charge weight The weight in kilograms of the explosive charge

Circuit tester An approved electrical instrument for testing firing circuits or the components thereof, such as detonators and cables/wires

Cleat Parallel cleavage planes or partings crossing the bedding and along which the coal breaks more easily than in any other direction

Codes Specify in detail the procedures that must be adopted to complete a particular activity, generally to conform with legislation


Collar The top of a drill hole, and may refer to the general area, including amount of hole left uncharged at the top of the hole or the beginning of a blasthole

Column charge A continuous charge of explosives in a blasthole

Coupling Describes the contact between the explosive and the wall of the blast hole

Critical diameter

The diameter of an explosive composition (sometimes called minimum diameter) below which detonation fails to occur or to continue indefinitely

Cut-off A break in a connection line for multiple blastholes, caused by flyrock or disconnection through people or vehicles travelling over the shot. Also refers to a misfire situation where the charge fails to detonate when a firing line or column charge is disconnected down the hole.

day box A container used at the work site for holding daily requirements of explosive

dead press Compressing a charge beyond its critical density, causing it not to detonate

deck charges Breaking the continuity of an explosive column in a blasthole to reduce the amount of charge in the blasthole or less commonly to reduce the amount firing on separate delays in the one blasthole

decoupling As opposed to ‘coupling’, decoupled charges are smaller in diameter than the diameter of the blasthole

deflagrating explosives

(Low) Explosives, which can be initiated by flame or spark, which have a lower velocity of detonation than 2000m/s

delay, delay detonators, delay blasting

Usually achieved by delay elements or micro-chips in detonators/electronic detonators, or by detonating connectors for detonating cord or signal tube connections

density The weight, generally in grams, g, of a volume, generally in cubic centimetres, cc, of rock or explosive or any other substance, where the density of water is 1g/cc

deputy Supervisor in charge of a section or district of a coal mine, and all employees working therein. The statutory duties, responsibility and authority of a deputy are set down in the relevant mining regulations

desensitisation Lack of sensitivity in an explosive, caused by dead-pressing or by shock that fails to initiate the explosive

detonating cord A cord with a solid core of (usually) PETN, and detonating at very high speed (7,000m/s), or virtually instantaneously, unlike signal tube. Detonating cord is consumed when initiated

detonation pressure

The pressure from the explosion

down line The line of detonating cord by which a primer is lowered into a blasthole, as opposed to a ‘trunkline’, which is the surface connecting detonating cord outside the blasthole

drift An inclined access from the surface to the coal seam or from coal seam to another coal seam or to the same seam that has been faulted-off

drifter A hand-held boring machine mounted on an air leg used to bore holes when driving drifts or drives

drilling line A line of drill holes some or all of which are not charged

drive A heading, drift, advancing place or face

drop cut A pattern commonly used when commencing the descent of a haul road in an open cut, similar to ‘box cuts’

elevated temperature

Material that is above 55oC and includes both hot ground and high temperature ground conditions as defined in AS2187.2(2006). Elevated temperature products – are explosive products that have been formulated and/or packaged and tested to withstand a nominated temperature for a recommended period of time before they will deteriorate or become unstable and possibly decompose violently or explode.

emulsion A mixture of Ammonium Nitrate in an oily emulsified liquid, to which other ingredients are added for sensitising and thickening the product. May be a bulk explosive or in cartridges

exploder A specially designed portable source of electrical/spark energy used to fire charges.

explosive Is any material or mixture of materials, which when initiated, undergoes a rapid chemical change with the development of heat and high pressure (see Australian Standard AS 2187.0)

exudation The appearance of oily globules of nitro-glycerine on the inside or outside of a cartridge wrapper

Face A wall of rock usually nearly vertical, either naturally formed or developed by blasting; the inbye end of the mine roadway, usually the working place for coal extraction


Firedamp Any mixture of methane and air is firedamp: if mixed in the range 5 to 15% (methane in air) the mixture will explode and has been the source of many explosions in coal mines - if above 15% the mixture will burn and hence the name firedamp. At one time firedamp used to be removed by deliberately lighting it, sometimes with the person being covered by a wet cloth when lighting or touching the methane. (see also methane)

Flammability A measure of the ease with which an explosive can be ignited

Flyrock Rock thrown far beyond the amount of ‘heave’ or ‘throw’ expected in a blast

Fracture Sometimes an old miners’ term for explosives

Fragmentation A description of the degree to which, or the size range when rock is broken. For example, good fragmentation means that the rock has broken to a size that doesn’t need any secondary breaking/blasting

Free face The face of rock that is nearest to the explosive charge

Freezing resistance

The ability of an explosive to withstand low temperatures. This may involve the addition of chemicals to reduce the temperature at which the explosive freezes, such as by the addition of nitrogylocol to nitroglycerine explosives to reduce the freezing temperature to –20°C

Fusehead Or match head - the fuse head of an electric detonator

Fume characteristics

The products, which includes gases, water vapour and finely divided solids, resulting from the explosion

Ground vibration

The movement of the ground as a result of the shock wave from the explosion. It is usually measured as the maximum speed of ground movement in millimetres per second “peak particle velocity”

Grunching Blasting the coal out of the solid seam without previous undercutting

Hazard Any plant or procedure at a place of work that has the potential to cause injury or damage to persons, property or the environment

Heading (1) roadways forming the openings in the direction of development of the panel, heading direction parallel to cleavage direction. (2) a roadway driven in the solid. (3) a roadway driven in the direction of advance of a district, e.g. Main headings, 2 s.w. Heading, etc

Heave Movement of the blasted ground caused by gas pressure forcing the ground to move forward

High explosives Explosives which are initiated by shock from another explosive, such as a detonator, primer or booster, having a velocity of detonation greater than 2000m/s

High temperature ground

High temperature blasting is defined as the blasting of material at 100oC or greater [AS 2187.2-2006 – Section 12.7]. See also ‘hot ground’

Hot ground Ground or material is defined as ‘hot’ if its temperature is 55oC or more but less than 100oC [AS 2187.2-2006 – Section 12.6.1]

Inbye The direction along a roadway towards the face thus going away from the surface entry

Incendivity Refers to the flame resulting from an explosion, mostly used in connection with the explosives ability as a ‘permitted explosives’ to be used for blasting in gassy or dusty situations

Inhibited product

Explosive products that chemically suppress the reaction between nitrates and sulphides.

Initiate Start the chemical reaction that is the detonation wave

Initiating explosives

Explosives which are used commercially to detonate other explosive charges

Instantaneous detonator

A detonator designed to have virtually no delay between initiation and explosion of the detonating charge

knee holes The next row of holes above the lifters in a round of shots

lifters The bottom row of holes in a round of shots designed to bring the floor of the excavation to the desired level

line drilling A method of smooth blasting, or perimeter drilling used to protect walls of an excavation from blasting. Some or all of these holes will not be charged. This is different to pre-splitting

loading density The weight of explosive required to load 1 metre of a blasthole – varies according to the blasthole diameter

magazine A store which is exclusively appropriated to the keeping of explosives

match head The fuse head of an electric detonator

maximum instantaneous charge, mic

The weight of explosive that detonates at the same time, which is normally defined as within an 8 millisecond period. The same as ‘Effective Charge per Delay’

methane (CH4) A gaseous compound of carbon and hydrogen naturally emitted from coal that can be explosive when mixed with air or oxygen between certain limits. Lighter than air, it comes out of the coal or surrounding strata


misfire A charge or part of a charge that has failed to explode

msds Material safety data sheet (MSDS) - is an information sheet that meets the Worksafe Australia Code of Practice for the preparation of Material Safety Data Sheets. A MSDS is supplied for each hazardous material offered for sale or transport by the manufacturer or supplier of the material.

multiple shotfiring

Firing a number of shots in a single round incorporating delay detonators

nitrous oxides, nOx

Includes a range of oxides of nitrogen resulting from an explosion; includes the very toxic nitrogen dioxide NO2, which gives the reddish-orange tinge to some blasting fumes and has a Permissible Exposure Limit (PEL) of 5ppm, also including nitric oxide NO with a PEL of 25ppm, also ‘laughing gas’ nitrous oxide N2O, and other oxides depending on the combustion

nonel See ‘signal tube’

Oxygen balance The amount of oxygen required for the explosive reaction to give optimum performance and fume characteristics

Overbreak Breaking of rock beyond the planned limit

Outburst A violent displacement of broken coal at the face caused by excessive gas or earth pressure, often associated with areas of weakness in the coal

Outbye (1) the direction along a roadway away from the face. (2) locations between the face and surface

PCF, penetrating cone fracture

Granular nitro-cellulose propellent powder that is a low explosive

Permitted explosive

Type of explosive approved under the mining regulations for use in coal mines/seams because its ignition temperature is below that required to ignite methane or coal dust

Pillar A block of coal left to hold up the roof and formed by driving a connected series of headings/bords and cut-throughs

Pop (pop shooting)

Breaking of large rocks by firing a charge within holes drilled into them

Powder factor The amount of explosive in kilograms required to break a cubic metre (or tonne) of rock in a particular situation

Precursor A material resulting from a chemical or physical change when two or more substances consisting of fuels and oxidisers are mixed and where the material is intended to be used exclusively in the production of an explosive. In order for such substances not to be categorised as a precursor, evidence shall be produced demonstrating that the substance cannot cook-off leading to a mass violent reaction. Such evidence may include physical and/or chemical testing/modelling, end use profiles, detailed risk analysis or by analogy.

Precursor building - A building, in which a precursor is normally manufactured, stored and transferred and where no additional processing of the material into an explosive occurs.

Precursor facility - A facility where precursors are manufactured, handled or stored.

Process building - A building licensed by the appropriate regulatory authority for the manufacture or handling of explosives, other than for immediate use.

Pre-splitting A shot fired prior to the main blast designed to create a crack in the rock, especially on the final wall of the excavation, and utilising the shock or shattering effect of the blast, not intending to utilise any heave, being fired with decoupled charges

Primer An explosive cartridge, package or unit used to initiate the main charge, often being the same charge as a booster, and generally fired by a detonator (a rare exception being safety fuse to fire a priming charge of black powder)

Protected works

Protected works are places that can be accessed by the public - The two classes of protected works are as follows:

(a) Class A: Public street, road or thoroughfare, railway, navigable waterway, dock, wharf, pier or jetty, market place, public recreation and sports ground or other open place where the public are accustomed to assemble, open place of work in another occupancy, river-wall, seawall, reservoir, above ground water main, radio or television transmitter or main electrical substation, a private road which is a principal means of access to a church, chapel, college, school, hospital or factory.

(b) Class B: A dwelling house, public building church, chapel, college, school, hospital, theatre, cinema or other building or structure where the public are accustomed to assemble; a shop, factory, warehouse, store or building in which any person is employed in any trade or business; a depot for the keeping of flammable or dangerous goods; major dam.


Pyrite A hard, heavy, shiny, yellow mineral, FeS2 or iron disulphide; generally in cubic crystals. Also called iron pyrites, fool’s gold, sulphur balls. May be applied also to copper pyrites, tin pyrites, etc., but iron pyrites is the most common sulphide found in coal mines or metalliferous mines that causes a problem. In its very fine form, it is likely to oxidise or combust at a rapid rate. The most likely material to be involved in ‘reactive ground’

Reactive ground

Rock that undergoes a spontaneous exothermic reaction after it comes into contact with nitrates. The reaction of concern involves the chemical oxidation of sulphides (usually of iron or copper, especially pyrite, and especially fine-grained pyrite, which is an iron sulphide) by nitrates and the liberation of potentially large amounts of heat. The process is unpredictable and can be so violent that it results in mass explosions.

Regulations Consist of specifications, prohibited practices, acceptable practices, approval mechanisms, and general detail to comply with the Act

Regulatory authority

The government agency or authority having jurisdiction for administering legislation covering the manufacture, transport, storage and handling of dangerous goods within a particular State or Territory.

Relative bulk strength

A comparison of the strength of an explosive with the same volume of ANFO, which is rated at a strength of 100%. This term is useful in comparing the effect of an explosive in a blasthole that has a different density to ANFO

Relative weight strength

A comparison of the strength of an explosive with the same weight of ANFO, which is rated at a strength of 100%

Rib The name given to the coal walls of the roadway: these are the sides of the pillars

Risk The chance that someone or something could be harmed

Rock dust See stone dust

Round (1) a series of shots connected and fired at the one time. (2) the selected pattern of holes drilled for multiple shotfiring

secondary blasting or breakage

Blasting of oversize rock that came from the primary blast

sensitivity A measure of the ease with which an explosive can be initiated by an external stimuli such as heat, friction impact or shock

shotfirer Person whose duty it is to place the explosive in a hole drilled in the face of the coal and then fire the explosive

shothole or Blasthole

A hole which is charged with explosives for blasting purposes

signal tube A generic term for Nonel or shock tube, which is a hollow tube containing HMX and aluminium on the inside wall, and is not consumed in a blast. It detonates with a flash that travels at around 1900m/s

sleep time The period of time an explosive may stay in a blast hole (say 30 days) and still be initiated reliably

smooth blasting

Method of drill hole placement when an excavation is to be made to close tolerances when shotfiring

socket See “butt”

spacing The distance apart of adjacent, side-by-side blastholes, that sit beside each other, or in the same row, as opposed to the distance they are apart in the direction of heave or rock movement, which is the ‘burden’

ssAn Security sensitive ammonium nitrate, containing more than 45% ammonium nitrate

stability The chemical stability of explosives

standards Document acceptable practices, developed and agreed to by consensus of statutory authorities, persons with industry experience, and others with specialist skills, and may be adopted by reference under legislation

stemming Inert material used in the collar area to confine the explosive gases in the blasthole

stemming stick A pole for dipping blastholes to tell how the explosive is rising in a blasthole, so that you can leave a length of blasthole uncharged and filled with stemming material – as opposed to a tamping stick or rod

stone dust Limestone (calcium carbonate) dust sprayed over roof, rib and face, and throughout the mine to render exposed coal dust inert, which is to reduce its potential to explode, especially following a gas explosion or combustion due to the flame of explosive detonations

Stone dusting is the operation of spraying finely ground limestone or other non- combustible and non-siliceous dust onto coal. The limestone particles mix with the coal dust and reduce the possibility of a coal dust explosion

strength The energy generated by the detonation of an explosive and the work the explosive is capable of doing – see ‘relative weight’ and ‘relative bulk’ strength


swell factor The ratio between the volumes of rock before and after blasting. Rock often ‘swells’ by 50% after the explosion but this can depend on the fragmentation

Tamping rod A wooden rod used for tamping or pressing explosives in blastholes

Throw Like ‘heave’ the movement of rock forward in a blast, while ‘throw’ might be in any direction, for example behind a shot where front holes do not move sufficiently

Toe Bottom of a blasthole, commonly referring to a lump in the floor remaining after a blast where the explosive was insufficient to break all of the rock as planned

undercut (1) to cut below or undermine the coal face by chipping away the coal by mining machine. (2) as for (1) above but part of the mining cycle when using explosives to remove the coal - creates an open area for the coal to expand to when the explosives are detonated – generally bringing down a lot of coal with a relatively small amount of explosive

undermanager A position holding responsibilities defined by the coal safety legislation. An undermanager is usually the person in charge of underground mining operations on a shift and is next in authority under a manager or deputy manager - requiring a 2nd class certificate of competency

velocity of detonation, vOd

The speed of an explosive reaction in converting an explosive from a solid to a gas

water resistance

The ability of an explosive charge to resist desensitisation from, or the effects of water when submerged at a given depth fro a period of time


A1APPENDIX 1 - NITROgLYCERINE DESTROYER

Liquid found in a box of nitroglycerine explosives might not be caused by water from condensation or saturated cartridges, but by migrating nitroglycerine, which has an oily feel and a distinct smell. However, you should always be alert to the liquid being dissolved ammonium nitrate (AN).

To determine whether cartridges are contaminated with nitroglycerine, take a clean glass and fill it with water. Place the damp cartridge of explosive into the glass; gently raise and lower the cartridge to free any liquid. If nitroglycerine is present, it will sink to the bottom of the glass and form globules separate to water because nitroglycerine is not water-soluble and has a higher density than water. If the liquid is AN, it will disappear into the water and not be a problem.

Nitroglycerine liquid can be destroyed by a solution made of the ingredients given in Diagram 20 (below).

Warning

Wear suitable eye protection and impervious gloves when mixing nitroglycerine destroyer solution, or treating areas affected by nitroglycerine. Ventilate the area well.

Ingredients Quantities

Caustic soda l60 g

Water 500 mL

Methylated spirits l000 mL

Acetone 250 mL

Diagram 20: Nitroglycerine-destroyer solution

Carefully add the caustic soda to water in a plastic or glass container, stirring until dissolved. Allow the mixture to cool for at least 30 minutes then add the methylated spirits and acetone while stirring. Aluminium, galvanised or zinc coated containers must not be used for making this mixture. Avoid all sources of ignition, smoking, and sparks when handling the mixture.

Important

Nitroglycerine-destroyer solution is extremely flammable and corrosive — so take adequate precautions.


A2APPENDIX 2 - BLAST MANAgEMENT PLANS

A2.1 INTRODUCTIONAll blasts shall be planned and designed to achieve the required outcome with minimum impact on the surrounding environment, below, on or above the soil or water surface. Records that detail the results of each blasting operation should be taken and maintained. This information assists in the planning and implementation of further blasts and provides documentation in case of incident or complaint.

A2.2 BLAST MANAgEMENT PLAN

A2.2.1 PuRPOse

The purpose of the blast management plan is as follows:

(a) Detail the objectives for the project or task.

(b) Identify risks and hazards associated with the objectives, including control and/or mitigation.

(c) Identify site-specific requirements including selection of personnel, training programs and communication systems.

(d) Introduce blast as part of the overall task in a planned manner.

(e) Control the blast process from design to initiation, evaluation and misfire treatment.

(f) Implement a review process to ensure that the objectives are met.

(g) Assure compliance with the approval/contract specifications.

(h) Assure the safety of the public, site personnel and surrounding properties.

Where required, the plan shall be submitted to a regulatory authority for authorization; otherwise the components of the plan shall be submitted to one or more competent persons, within the organization conducting the blast, responsible for such authorization.


A2.2.2 COnTenTs

A blast [management] plan, should include, but not be limited to, the following:

(a) Location of the proposed blasting.

(b) Description of the proposed blasting.

(c) Permits/licences required for the project.

(d) Identification and position of the person responsible for the project including project safety and security.

(e) Identification and position of person who has given approval to use explosives on the project.

(f) Key appointments and responsibilities.

(g) Shotfirer’s details.

(h) Details of the risk management assessment.

(i) Details of adjacent structures or services that influence the blast design.

(j) Details of reports, drawings and records consulted.

(k) Layout plan of the blast including drilling pattern and hole depths.

(l) Detonation sequence/effective charge mass per delay (MIC)/powder factor.

(m) Type of explosive to be used and quantity required.

(n) Method of initiation.

(o) Type of firing equipment and procedures.

(p) Drilling procedures.

(q) Explosive loading and charging procedures.

(r) Explosive storage and handling procedures.

(s) Security procedures for the site and the blast, including explosives.

(t) Environmental considerations for airblast overpressure, ground vibration.

NOTES:

1 Information on air blast overpressure and ground vibration is given in Appendix J.

2 Information on flyrock and fly is given in Appendix E.

(u) Details of communication systems.

(v) Warning procedures.

(w) Traffic management plan.

(x) Proposed dates and times of blasting.

(y) Details of the exclusion zone.

NOTE: See Appendix L.

(z) Method of notification to owners and occupiers of structures, and providers of services adjacent to the blast.

(aa) Influence of weather.

(bb) Loading in poor light conditions or reduced visibility.

(cc) Cessation of explosive-related activities during electrical storms.

(dd) Misfire management system.

(ee) Post blast assessment and inspection procedures.

(ff) Provision for post-blast comments.

(gg) Signature spaces for the plan author, shotfirer and person who approves the plan.

A2.3 BLAST RECORDSDetails of blasts should be taken and maintained, including but not limited to the following:

(a) Environmental conditions at the time of the blast.

(b) Monitoring equipment including type, serial number and location.

(c) Details of measurements recorded during the blast.

(d) Details of flyrock or fly.

(e) Details of incidents and complaints.

(f) Comment on the results of the blast.

(g) Proposed modification to the blast plan for future shots.

Provision for this information may be made on the blast plan.

A2.4 TUNNEL AND MINE DEVELOPMENT BLAST RECORDElements of safety associated with tunnel blasting, such as the possible presence of hazardous atmospheres and inrush should be recorded.


NOTES


NOTES


NOTES

Documents

SC LR4-UGC Blast Planning