Introduction to Hazardous Evaluation Techniques

• Guidelines for Hazardous Evaluation Procedures (1992 by AIChE).

• Second Edition with Worked Examples.• Center for Chemical Process Safety

(CCPS).• American Institute of Chemical

Engineers (AIChE).

Hazard Evaluation Techniques

1960 - 2001 1960 - 2001 1965 - 2001 1970 - 2001 1972 - 1974 1974 - 2001

Safety Check Lists Relative PHA What if HAZOPReview Ranking

Walk Historical ICI Mond Preliminary Brainstorming HazardsThrough Lists Index Hazard OperabilityInspection Analysis Analysis

Yes / No Dow FEIHazardous Mtls Line by LineHazardous Opns Deviation

Analysis

This presentation only considers the HAZOP technique.

HAZOP

• HAZOP was developed by Lawley (1974) of ICI. Based on early account by Elliott & Owen (1968).

• Hazop studies are carried out by an experienced, multidisciplanary team.

• Review all physical aspects of a process (lines, equipment, instrumentation) to discover potential hazards.

Basis for HAZOP

• The basis for a HAZOP is a critical examination of information found in a word model.

• It includes a flowsheet, a plant layout, equipment specification or a P&ID, (Piping and Instrument Drawing).

Hazop Includes

1 Intention2 Deviation3 Causes4 Consequences

(a) hazards (b) operating difficulties

5 Safeguards6 Recommendations / Actions

Hazop Guide Words

NO or NOT Negation of intention No Flow of A

MORE Quantitative increase Flow of A greater than design flow

LESS Quantitative decrease Flow of A less than design flow

AS WELL AS Quantitative increase Transfer of some component additional to A

PART OF Quantitative decrease Failure to transfer all components of A

REVERSE Logical opposite of intention Flow of A in direction opposite to design direction

OTHER THAN Complete substitution Transfer of some material other than A

More recent computerization techniques use a Standard Set Of Generic DeviationsFor Specific Section Types. See Dev'ns tab for examples.

Common HAZOP Analysis Process Parameters

Flow Time Frequency Mixing

Pressure Composition Viscosity Addition

Temperature pH Voltage Separation

Level Speed Toxicity Reaction

Prepare for the Review

AttitudePreparation Meeting Leadership

HAZOPReview By Documentation Follow-up

Team

Knowledge Info for studyExperience Teams HAZOP P&Ids, Layout

Experience

Table

Deviation Causes Consequences Safeguards Action

HazopFlowSheet

Select a processsection or operating step

Explain design Repeat for allintention process sections

Select a process Repeat for allvariable or task process variables

Apply guide word Repeat for allto process variable guide words

Examine Develop actionConsequences itemsassociated with deviation

List possible Assess acceptabilitycauses of of risk based on deviation consequences

Identify existingsafeguards toprevent deviation

Hazop PitfallsPoor understanding by management of the HAZOP procedure

An Ethylene plant has 100 P&IDs, 625 equip't items. 625 itemsConsider 5 variables, Pressure, Temperature, FlowComposition and Function. 5 variablesConsider 6 Guidewords, None, More of, Less ofPart of, More than and Other than. 6 guide wordsQuestions to be answered = 18750 questionsConsider 5 minutes per question = 5 min./questionTime for ethylene plant HAZOP study = 93750 minutes4 hour, 240 minutes sessions per day = 250 minutes/dayNo. working of days = 375 daysDays per week = 5 days/weekNo. of weeks to complete HAZOP for plant = 75 weeks

Other Pitfalls

• Inexperienced HAZOP team.

• Inadequately trained or in-experienced leader.

Common Hazop Mistakes

• Failing to establish a "safe" environment for team members.

• Consequences of events not carried to conclusion.

• Taking unwarranted credit for safeguards.

• Too little credit given for safeguards.

Hazop Mistakes Cont’d

• Failure to make recommendations as specific as possible.

• Poor record keeping of HAZOPS.

• Failure to HAZOP start-up and shut-down procedures.

• P&IDs not up-dated or poorly constructed.

Hazop Mistakes Cont’d

• A HAZOP is performed in lieu of properly executed design reviews.

• Wrong technique for system being reviewed (See spreadsheet titled Fig 5.3).

HAZOP Example

To Compressor Inlet

Teams tend to quickly identify alarms, shut-downsand controls, and claim them for safeguards.

An alarm not tested may not work when called uponInlet Line to do so.

Nuisance alarms are frequently bypassed and arenot effective as safeguards.

Often operators are not monitoring control panel.

Valve in manual Automatic control routines are often set in manualmode.

FV 1

LAH

LIC 1

Standard Set of DeviationsID No. Deviation Column Vessel Line Exchanger Pump Compressor

1 High Flow X2 High Level X X3 High Interface X4 High Pressure X X X X5 High Temperature X X X X6 High Concentration X X X7 Low / No Flow X X8 Low Level X X9 Low Interface X

10 Low Pressure X X X X11 Low Temperature X X X X12 Low Concentration X X X13 Reverse / Misdirected Flow X X14 Tube Leak X15 Tube Rupture X16 Leak X X X X X X17 Rupture X X X X X X

Typical Hazop WorksheetCompany Nova Revision 0 Date 02-Jun-97Location Corunna Dwg No. Cor -123-4567 Page 1Leader RAH Proc Des JB Research Op TechScribe GFR Instr'ts GH Electrical HH OtherProd'n PM Mech FD Safety MN Other

Node No. 1 Describe Transfer Ethane from Deethanizer to C2 KO Pot

Intention The intent is to transfer 150,000 lb/hr of C2/C2= mix at 300 psig and at -30 °F for the startup period.

Guide Wrd High Param Flow Dev'n High Flow

Possible Causes1 FV-1 Wide open2 Line break.3

Consequences1 High level in KO pot with liquid carry-over to compressor with serious damage to rotor. Potential hydrocarbons release.2 Potential hydrocarbon release.3

Safeguards1 High level alarm LAH-12 High - High level alarm HHLA - 1 shutdown.3 Vessel inspection yearly.

Recommendation / Actions Respib By Date1 Consider limiting flow orifice, auto SD trip on High-High level, smart check valve. 1 JB 01-Jan-992 Determine extent of typical hydrocarbon release. 2 PM 15-Jan-993 Set-up vessel inspection yearly. 3 FD 30-Jan-99

Check List Example1 Changes In Quantity a High Flow 1 Pump racing, delivery vessel pressure lost,

suction pressurized, scale dislodged, leak in heat exchanger

Loss of automatic control

b Low Flow 2 Pump failure, scaling of delivery, presence of foreign body, poor suction condition, cavitation, leak in heat exchanger, drain leak, valve jammed

Operator error

c No Flow 3 Pump failure, delivery vessel overpressurized, gas blockage, presence of foreign body, scale, sediment, suction vessel empty.

Failure of joint, pipe, valve, trap, bursting disc, relief valve.

d Reverse Flow 4 Pump failure, pump reversed, delivery vessel over pressurized, poor isolation, gas locking, surging, back siphoning.

Check List Cont’d

2 Changes in physical condition

a High or Low pressure

1 Boiling, cavitation, freezing, chemical breakdown, flashing, condensation, sedimentation, scaling, foaming, gas release, priming, exploding, imploding. Changes in viscosity, density. External Fire, Weather conditions, Hammer.

b High or Low Temperature

2 same as 1

Check List Cont’d3 Changes in chemical

conditiona High or Low

Conentration1 Changes in proportion of mixture, in water or

solvent content.b Contaminants 2 Ingress of air, water, steam, fuel, lubricant,

corrosion products, other process materials from high pressure system, leakage through heat exchangers. gas entrainment, spray, mist.

4 Startup and Shutdown Condition.

a Testing 1 Vacuum, pressure testing with with harmless material.

b Commissioning 2 Concentration of reactants, intermediates

c Maintenance 3 Purging, venting, sweetening, drying, warming. Access, spares.

5 Hazardous Pipelines a Pipeline registration

1 Should this pipe be considered for registration?

End of HAZOP Presentation.

• Presented to ES-317y

• 27 Feb, 2001

• By R.A. Hawrelak