Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Electrical & Welding
Serious Exposure
Electrocution is one of the top four causes of construction fatalitiesNearly half of those fatalities were
the result of contact with overhead power lines OSHA is focusing more attention to
these exposures
Applicable Standards
Electrical standards are among the most frequently cited by OSHANo Lock Out/Tag OutImproper Wiring MethodsInadequate Components and Equipment
OSHA references the following for guidelinesElectric Safety Requirements for Employee Workplaces and
codes (NFPA 70E)
Basic Terminology
Conductor – A material that has very low resistance to the flow of electric currentInsulator – Material that resists electric currentGrounding – A low resistance path to the earth
for electric currentAmps – The amount of electricity flowingVolts – The force at which the power flows
Grounding• Service Ground – Protects machinery/equipment• Equipment Ground – Protects worker from tool
malfunction• 2 options for safe grounding:
• Assured Grounding Program• Written Program• Testing (continuity and terminal connection)• Test Schedule• Completed by Competent person
• GFCI (Ground Fault Circuit Interruption)
Ground Fault Circuit Interruption
• Must be provided for all 120v single phase 15 and 20 amp circuits that are not part of the permanent wiring
• Permanent wiring using an extension cord is considered temporary power and requires a GFCI
• All temporary power sources must have GFCI protection either at main box, extension cord, or tool.
Ground Fault Circuit Interruption
Ground Fault Circuit Interrupters (GFCI’s) sense changes in current (5 milliamps) and stop energy flow.Devices stop current in 1/40
of a secondNever bypass any protective
system or device designed to keep you from contact with electrical current.
Electric Shock
• Body becomes part of the electrical current• Current enters the body at one point and leaves at
another (path to ground)• Shocks can occur when a person contacts:
• Both wires• Wire to ground• Any conductor that is energized
Physical Effects
Amps are the true measure of current absorbed, not voltsWe are good conductors, the
human body is 70% waterInvoluntary muscle contraction
is the reason we are affectedCan’t let go of energized objectBreathing is impairedHeart rhythm is disrupted
Physical Effects
1 mA
16 mA
20 mA
100 mA
2 amps
15 to 20 amps
Barely perceptible
Max current an average man can grasp and let goParalysis of respiratory muscles
Ventricular fibrillation threshold
Cardiac standstill and internal organ damage
Current required to trip common household breaker
Influencing Factors of a Shock
Circumstances that affect the outcome of an electric shock;Circuit voltageThe bodies external (skin) and
internal resistanceTotal current flowing through the
bodyCurrent pathThe duration of the shock
Employer Responsibilities
Equipment must be:Free from recognized hazards Suitable and identified through listing,
labeling, or certification of purpose.Designed with adequate mechanical
strength and durability
Other items for consideration Electrical insulation Heating effects /conditions of use Arcing effects Use classifications
GuardingLive parts of electrical equipment operating at 50 volts or more
must be guarded against accidental contact.Means of acceptable guarding include:Isolation in a cabinet, room, or vault accessible only by
qualified personsUse of partitions or screens to exclude unqualified personsElevation of eight feet or more above the floor
Electric installations over 600 require special protectionmetal-enclosedVaultcontrolled by lock
Lock Out / Tag Out
LOTO written program Components
Documented energy control proceduresEmployee Training
programInspection
program
Lock Out / Tag Out
Purpose is to draw attention to and disable a live energy source during service and repair work.Lock Out physically disables
the energy source, Tag Out provides a warning onlyOnly the employee who
placed the lock or tag may remove it!
Safe Power Shutdown- 5 Steps -Preparation and Notification– Understanding
energy source and alerting all affected employees
Shutdown – De-energizing procedureIsolation – Properly locking all power sourcesLock & Tag Application
Color coding for different tradesEmployee assigned locksPhoto tags, helps locate employee, makes
associationControl and Verification– Control stored and
residual energy with locks in place
Re-energizing- 3 Steps -
Inspection – checking the work area and surrounding machinery and for employeesNotification – Make notice
to all affected employees as to what will be re-energizedRemoval of Tags and Locks
Tags and Locks
Tags and Locks must be:Durable – resist conditions of environmentStandardized – color code and formatSubstantial – strong enough to minimize false
removalIdentifiable – clear message, know who it is
protecting
Extension Cords
Service RatingsHard Service (types S, ST, SO, STO)
Junior Hard Service (types SJ, SJO, SJT, SJTO)
Home use, small appliance (type SP)
Cords with missing ground prongs, broken insulation, crimping or crushing must be removed from service.
Splicing is prohibited but new end can be installed Unplug at the receptacle Any cord that has to cross a pthway must be protected OSHA considers an extension cord temporary power, no matter the power
source!
Portable GeneratorsNever use a generator indoors or
in an attached garage.Use extension cords with adequate
duty ratings. To prevent electrical shock, make
sure your generator is properly grounded.
Do not store fuel indoors or try to refuel a generator while it's running.
Turn off all equipment powered by the generator before shutting it down.
Other Considerations
Environmental Deterioration of Equipment - Unless specified for use in such an environment, no conductors or equipment should be exposed to; Damp or wet locations Gases, fumes, vapors, liquids, or other deteriorating agents Excessive Temperatures
Electrical ChecklistExtension cords:
- No crimping or crushing- No missing insulation- No signs of stress at plug
All extension cords out of high traffic areas:
- Road ways (protective cover)- Driveways- Hallway, entrance, stairwell
Lock Out / Tag Out plan for all maintenance operations
Equipment rated for duty and environment
Proper PPE when necessary GFCI protection at box, cord, or tool
Awareness of all overhead power lines
All tools double insulated
Pre-job identification of all underground utilities
Generators must have earth ground
WeldingPotentially Hazardous Fumes and Gases Fumes – Solid particles that originate
from the welding media, base metal, orcoating
Gas – Generated by the shielding gas or process radiation Nickel Zinc Iron Oxide Copper Cadmium Fluorides Manganese Chrome & Gases
Effects of Overexposure Acute Effects
Irritation of eyes, skin, respiratory system
nausea, headaches, dizziness
Metal Fume Fever Asphyxiation (confined
space) Chronic Effects
Central nervous system impairment
Respiratory illness Reproductive disorders Possible links to
Parkinson’s
Radiation
Visible – intense light emitted during welding operations
Infrared - produced by electric arc and other flame cutting equipment
Ultraviolet - generated by all arc processes
Radiation Effects - Influencing Factors
WavelengthIntensityDuration of
exposureExposure may result
in skin burns or eyedamage
Common Welding Techniques
MIG WeldingTIG WeldingMAPP GasOxy-fuel Welding
MIG Welding “Metal Inert Gas” Semi-automatic or automatic arc welding process
in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun.
Can use alternating or direct current, DC is most common
Typically used with steel Fast welding technique
TIG Welding “Tungsten Inert Gas”Uses a nonconsumable tungsten electrode and
filler metal to produce the weld.A shielding gas such as argon protects the
process from atmospheric contamination Commonly used with Aluminum, Magnesium,
Copper, light gauge Stainless Steel Slower than other welding techniquesHarder to master than other forms of welding but
produces higher quality and stronger welds
MAPP Gas “Methyl Acetylene Propodiene” Consists of LPG mixed with MAPPDoes not require dilution or special container
fillers during transport which allows a greater volume of gas to be transported at the same givenweight
Most commonly used for brazing and soldering Ideal for aluminum and copper
Oxy-fuel Welding“Oxyacetylene Welding” aka Gas WeldingTwo pieces are heated to a temperature
that produces a shared pool of molten metal.The molten pool is supplied with
additional metal called filler.
Safe Work Practices The surrounding work area should be clean and free of
potentially combustible material A fire extinguisher should be kept on hand at all
times Good ventilation is a must for all welding operations Personal protective equipment (PPE) should include eye
and face protection as well as protective clothing Less toxic materials should be substituted when
possible Cadmium-free silver solders Asbestos-free electrodes
Pre-Shift Inspection
Leads – insulation breech, kinks Torch – tip, valves, tool bodyHoses & Fittings Bottles & Valves Cart or other CG Bottle Support Surrounding Area Fire ProtectionAny defective equipment must be replaced,
repaired, or removed from service
Personal Protective Equipment
HelmetMust Comply with
ANSI Z87.1Most equipped with
auto-darken features, 1/10,000 of a second
OSHA 1926.102Tables E-1 and E-2 specify minimum protection levels
Personal Protective Equipment
GlovesANSI Z49.1Must be flame resistantGloves should be in
good shapeMust resist potential
electric shock from welding unit
Personal Protective Equipment
ApronANSI Z49.1 Produced in
variety of fire retardant materials LeatherNomexChemically treated
textiles
Compressed Gas Cylinders
Typical Oxygen cylinder pressures are around 2600 lbs/in²
Oxy fittings should be kept clean and free of oil and grease
Hose colors determine use:Red – fuel gas hoseGreen – OxygenBlack – Inert gas
Compressed Gas Cylinders
Cylinder valves must be protected at all times
Cylinders should be stored in an upright and secure position
The tilt and roll method is accepted practice for movement, never attempt to hoist with chokers
Valve caps must be secure any time the cylinder is not in use
When stored, oxygen cylinders should be separated from other gas cylinders. The required separation is 20’
or A five foot high fire wall with an
approved fire-resistance rating
Welding Torch - Cutting Torch Comparison
Cutting Torch Safety
Take appropriate precautions forflooring surface
Work benches made of steel or other fire retardant material isacceptable
Adequate ventilationConfined SpacesToxic Fumes
Cutting Torch Safety
Appropriate personal protective equipmentControl potentially combustible materials
around work areaFire extinguisher handy at all timesEquipment maintenance
Safe Welding ChecklistFamiliarization with all applicable Material Safety Data Sheets (MSDS)
Surrounding area free of potentially combustible materials
Leeds should be fully insulated, no kinks or deformation
Fire extinguisher readily available, fully charged and functional
Torch tip, valves, and tool body in good working order
Proper face, hand, and body protection in use
Hoses and fittings tight and free of wear, dry rot
Surrounding work areas protected by welding curtains
Bottles secured and upright whether stored or in use, cap secured
Adequate ventilation for all processes at all locations
Bottles free of excessive corrosion, no dents, collar threads intact, clean fitting
Insure proper grounding of welding machine
Valves and gauges secured and operational
Any defective equipment replaced or repaired prior to the start of work