Electrical Hazards Temporary Wiring and Lighting Systems.
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Transcript of Electrical Hazards Temporary Wiring and Lighting Systems.
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ElectricalElectricalHazardsHazards
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Temporary Wiring and Lighting Systems
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Electrical Harm
Estimated Effects of AC Currents (U.S. Standard 60 Hz)
1 milliamp (mA)
Barely perceptible
16 mA Maximum current an average man can grasp and “let go”
20 – 30 mA Paralysis of respiratory muscles
100 mA Ventricular fibrillation threshold
2 Amps Cardiac standstill and internal organ damage
15/20/30 Amps
Common U.S. household breakers
PATH: Harm is related to the path by which current passes through the body.
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Ground Fault Circuit Interrupters(GFCI)
• Monitors current flow between the hot and neutral wires
• Trip between 4-6 mA in 1/40th of a second
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How GFCIs Work
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Assured Equipment Grounding Program
• Inspection is your primary protection
• Best practice recommends documented testing every 3 months
• Color coding most common:
Winter Spring Summer Fall
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Reverse Polarity Diagram
Hot
Neutral
Switch
Tool could be hot with the switch offHot wire and neutral wire are reversedEven though a switch is off, the circuit could be hot
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Electrical Extension Cords
• The primary insulation is cut• If the insulation was also cut on
the conductors, exposing bare wires, they could come in contact with someone
• Damage is often caused by repeated stretching or being run over
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Electrical
• Wiring like this must be protected in closed boxes
• There is the potential of electric shock from loose wire nuts or exposed conductors
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Electrical Panel Boxes
• Live electrical panels must be completely covered with a hard cover (original intended equipment)
• Employees could be exposed to live wires around the perimeter of this box
• No Cardboard!
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Arc Flash Prevention
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An electric arc:
• Typically lasts less than a second• Has extremely high radiant (heat) energy• Is explosive in nature (exerts great force)• Can ignite or melt conventional work
clothing
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Pressure Waves > 2000 lb/psf
Copper Vapor:Solid to VaporExpands by67,000 times
Molten Metal > 1800 ° F
Intense Light
Hot Air >500 ° F
35,000 °F
Shrapnel > 740 mph
Sound Waves >140db
Electrical Arc
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NFPA 70E Requirements
• Arc flash boundaries must be known• Safe approach distances established and
maintained• Marking equipment relative to hazards• Electrically safe (voltage rated) tools• PPE (ATPV)• Training
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The Best Way to Work on Energized Electrical Equipment?
• Shut it down and lock it out • Establish an electrically safe
working condition
DON’T!
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Overhead Powerlines
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The Sad Reality
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Power Line Facts
• Overhead lines are typically not insulated. Any covering is generally a weather protection, not insulation.
• Over 90 percent of the contacts occur on overhead distribution lines
• Operators are normally safe if they stay on the equipment
• Ground personnel are over 8 times more likely to be killed
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Electrical Damage to the Body• If you touch a power line,
electricity will attempt to travel through your body
• When electricity travels through the body, it heats up and burns body tissue internally
• Electricity leaves the body violently, causing burns or even blowing an exit hole
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Maintain Safe Working Clearance
• All equipment – ladders, scaffolds, cranes, trucks, forklifts, etc. – MUST maintain a minimum 10 foot clearance from 50 kV or less
• Add .4 inches for every kV over 50 kV
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MINIMUM 10' Distance
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Ensure Adequate Clearance
• Install flag warnings at proper distances
• If it is difficult for an operator to see the power lines, designate a spotter
• If you cannot maintain adequate clearances, you must have the power company insulate, move or de-energize the line
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• Insulated Sleeves Must be Installed by the Utility Company
• Allow Sufficient Time• Must Still Maintain
Minimum Line Clearance Distance
Insulated Sleeve
Insulated Blanket
Barrier Protection
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The Ground May Be Hot!
• Electricity dissipates with the resistance of the ground
• As potential drops, fields develop around the electrified machine
• If you step across a line of unequal potential, you could be electrocuted
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If Contact Occurs
• Stay on the machine if possible
• Warn all others to stay away
• Notify power company immediately
• Attempt to move away but assure line is not “connected”
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Bail Out Procedures
• If you must get out, jump with your feet together
• Do not touch the machine
• Hop or shuffle out of the area
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Lightning?
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Lightning Safety• If you hear thunder, suspend
all outdoor activities!• If you see Lightning, seek a
shelter immediately!• Cranes - lower boom and
stop operations and move to shelter
• Those people who are working at heights - climb down and take shelter in a protected building / safe area
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Incident FreeIncident Free
• Planning – Installation of temporary power– For working around electrical panels– Work around overhead power lines
• Training– Workers about circuit contact– For Arc-flash prevention and protection– For safe work around overhead power lines
• Inspection– Electrical tools and equipment– Electrical panels for live circuits– Temporary wiring & lighting
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Incident FreeIncident Free
• Oversight– Electrical installations– Site issues around power lines
• Lessons learned– Accidents with circuit contacts– Arc-flash incidents– Power line contacts
• Re-evaluate – Temporary electric specifications– Electrical work practice
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Competent Person
• A competent person is someone who:– Is capable of identifying existing and
predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees, and
– Has the authorization to take prompt corrective measures to eliminate them
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Incident FreeIncident Free
• Planning
• Training
• Inspection
• Oversight
• Lessons learned
• Re-evaluate
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SummarySummary
• The focus four hazards are responsible for the majority of physical, financial, and emotional losses in construction — and they exist on nearly every jobsite.
• It takes a well-trained crew (the entire crew!) and lots of pre-planning to recognize and respond to those hazards. Safety is everyone's responsibility — ALL of the time.