Sheet 14Domain 2 of 5 · Hazard Identification and Control
Electrical safety, lockout and hot work for the STSC
A cord pinched under a door, a panel cover leaning against the wall, a cylinder cart parked in the stairwell: you make each of these calls on a walk, often in under a minute. Electrical safety on a construction site means temporary power, cords and lockout, and this STSC sheet adds hot work because welding and cutting bring electrical and fire hazards to the same corner.
Construction electrical rules sit in 29 CFR 1926 Subpart K (1926.400 to 1926.449). They are short on theory and long on site equipment: temporary wiring, flexible cords, ground-fault protection for the receptacles workers plug tools into, and clearances from overhead lines. The ground-fault rule for temporary power, 29 CFR 1926.404(b)(1), deserves a slow read.
Lockout/tagout (LOTO) is the other half. The construction rule for de-energized circuits is 29 CFR 1926.417, and concrete and masonry equipment gets its own lockout line in 1926.702(j). The step-by-step energy-control procedure in most safety training comes from the general-industry standard, 29 CFR 1910.147.
Stored electrical energy in capacitors and batteries
Hydraulic pressure trapped in lines and cylinders
Compressed air in receivers and hoses
Gravity: raised booms, buckets, forms and counterweights
Springs and other stored mechanical tension
Heat and chemical energy in lines, kettles and tanks
Talking point 03
GFCI and circuit breaker do different jobs
What each device watches forscroll →
Point
Ground-fault circuit interrupter (GFCI)
Circuit breaker
Watches for
Current leaking to ground, such as through a person
Too much current in the circuit
Protects
The worker holding the tool
Wiring and equipment from overheating
Trips on a shock through a hand
Yes, fast enough to limit the shock
Usually not; the current is too small to register
Where the device sits
Built into a receptacle, a cord set or a breaker
In the panelboard
A tripped GFCI is a signal to find the fault. Bypassing it with a cord or outlet that lacks one removes the only protection the worker had.
Talking point 04
Lockout and live-power drill
Panels, cords, lockout on pumps and mixers, power lines, welding near combustibles and empty drums.
Card 1 of 16 · 0 right
Card 1
A mechanic will reach into a concrete conveyor to clear a jam. The operator has pressed the stop button. What should the supervisor require BEFORE the mechanic reaches in?
Pick an answer. A short note for each option, A to D, appears here.
AA stopped belt shows only that the conveyor is not moving now; a stop button is a control circuit, not an energy-isolating device.
BA sign without isolation depends on everyone seeing and obeying it, and it does not remove the energy.
CCorrect: Before anyone reaches in, the energy source must be isolated, locked and tagged, and zero energy verified by trying the controls.
DPosting a person at the controls relies on behavior, and that person can be distracted or called away.
Card 2
An audit found several temporary power panels without working GFCI protection. The electrical foreman later reports the items 'fixed.' What is the BEST way for the supervisor to verify the corrective action?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: A corrective action is verified when someone checks in the field that the fix is in place, and testing the GFCIs confirms they actually work.
BA line in a weekly report shows the work was claimed, not that the GFCIs were installed and function.
CWaiting for the next audit leaves workers exposed to shock hazards for months if the repair was incomplete.
DA signed statement documents a claim but does not verify that protection is actually in place.
Card 3
A written lockout procedure exists for a concrete pump, but the supervisor suspects crews take shortcuts. Which method BEST shows whether the procedure is followed in practice?
Pick an answer. A short note for each option, A to D, appears here.
AA foreman's written certification describes intentions rather than what crews actually do in the field.
BTraining records show instruction was given, not that the procedure is applied correctly on the job.
CA current binder on site confirms the procedure exists, not that crews follow it.
DCorrect: Observing the task and talking with the crew reveals what is actually done in the field and why shortcuts happen.
Card 4
During an inspection, a supervisor finds an extension cord run through a hole in a wall to power a site office's lights for the last three months. What is the BEST corrective action?
Pick an answer. A short note for each option, A to D, appears here.
AA heavier cord is still a flexible cord used as a substitute for fixed wiring and run through a wall.
BCorrect: Flexible cords may not substitute for a structure's fixed wiring or run through holes in walls, so proper wiring is needed.
CGFCI protection does not fix a cord being used as permanent wiring through a wall.
DA sleeve protects the cord at one point, but the cord is still being used as fixed wiring.
Card 5
Electricians will work on a circuit that can be energized from both the main panel and a portable generator transfer switch. What does OSHA require before the work begins?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: De-energized circuits must be rendered inoperative and tagged at every point where they can be energized, including an alternate generator feed.
BOpening the nearest breaker leaves the generator transfer switch able to backfeed the circuit.
CTagging only the transfer switch leaves the main panel able to energize the circuit.
DA circuit with an alternate feed can be backfed even when the main breaker is open, so the main panel alone is not enough.
Card 6
A welder is joining steel next to wood blocking that cannot be moved, and the supervisor has posted a fire watch. Under 29 CFR 1926.352, how long must the fire watch continue after welding stops?
Pick an answer. A short note for each option, A to D, appears here.
ALeaving when the welder packs up ends the watch exactly when hidden embers are most likely to flare.
BThe 30-minute figure comes from general industry rules and NFPA 51B, and the construction rule sets no fixed number of minutes.
CA 60-minute watch with a later recheck is a site practice, not the construction requirement.
DCorrect: The construction hot-work rule requires the fire watch to continue for a sufficient period after work to detect and extinguish smoldering fires.
Card 7
An electrician is assigned to retighten terminations inside a 480-volt panel that feeds the site trailer. The work does not require the panel to be energized. What is the BEST control?
Pick an answer. A short note for each option, A to D, appears here.
AA standby electrician adds help after an incident but does nothing to remove the shock or arc-flash hazard itself.
BArc-rated clothing reduces injury severity if an arc occurs, but it is PPE and ranks below removing the energy.
CCorrect: When the work does not require energized conditions, de-energizing, locking out and verifying absence of voltage eliminates the shock and arc-flash hazard.
DInsulated tools and gloves are protective measures for energized work, which is justified only when de-energizing is infeasible.
Card 8
A mortar mixer has been shut down, and its disconnect has been locked and tagged so a laborer can clear the drum. What should be done next, before the laborer reaches into the drum?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: After lockout, trying the start control confirms no energy remains, and the controls are returned to off before work begins.
BA stopped drum shows only that it is not moving now, not that it cannot be restarted.
CA locked handle can hide a failed switch or the wrong disconnect, which only a try-out reveals.
DAsking the operator relies on memory and word of mouth instead of verifying that the energy is isolated.
Card 9
Two subcontractors will service the same air-handling unit on the same day. One uses individual personal locks; the other uses a single crew lock. What is the BEST approach?
Pick an answer. A short note for each option, A to D, appears here.
AA single lock held by someone else removes each worker's personal control over the energy that could hurt them.
BInformal conversation is not a procedure, and one crew could re-energize while the other is still exposed.
CIncompatible procedures running in parallel on one unit risk one crew restoring energy while the other is working.
DCorrect: When several employers work on the same equipment, their energy-control procedures must be coordinated so every worker is protected.
Card 10
A supervisor finds a temporary lighting circuit with damaged insulation and exposed conductors along a corridor where several trades work. What is the MOST effective control?
Pick an answer. A short note for each option, A to D, appears here.
AElectrical tape does not restore rated insulation, so the damaged circuit stays a shock hazard in service.
BBarricades and signs are administrative controls that leave live, exposed conductors in a busy corridor.
CRubber gloves are PPE that protect only those wearing them and leave the energized hazard in place.
DCorrect: Removing the energy eliminates the shock hazard, and the de-energized circuit is tagged out and repaired before reuse.
Card 11
A contractor supplies temporary power to hand tools from 120-volt, single-phase, 15- and 20-ampere receptacles that are not part of the building's permanent wiring. What ground-fault protection does OSHA require?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: Temporary 120-volt, 15- and 20-ampere receptacles need either GFCI protection or an assured equipment grounding conductor program.
BLimiting GFCIs to wet locations is a common misconception; the rule covers all such temporary receptacles.
CDouble-insulated tools do not exempt the receptacle from GFCI protection or an assured grounding program.
DAn assured grounding program tests cords at intervals of no more than three months, not once a year.
Card 12
What is the primary hazard control when welding must be performed near flammable materials that cannot be relocated?
Pick an answer. A short note for each option, A to D, appears here.
AA fire watch helps catch fires but does not stop sparks and slag from reaching the combustibles in the first place.
BCorrect: When combustibles cannot be moved, guards or fire-resistant shields must confine the heat, sparks and slag.
CWetting combustibles may help, but it does not reliably stop sparks and hot slag the way a shield or barrier does.
DLower amperage still throws sparks and slag. It does not protect combustibles that cannot be moved.
Card 13
Masons plan to erect a supported scaffold along a wall where an uninsulated 13.8 kV distribution line runs parallel to the building. The utility will not de-energize or move it. What minimum distance must the scaffold and the conductive materials handled on it keep from the line?
Pick an answer. A short note for each option, A to D, appears here.
AThree feet applies only to insulated lines under 300 volts. An uninsulated 13.8 kV line needs much more room.
BCorrect: Scaffolds and the conductive materials handled on them must stay at least 10 feet from uninsulated lines up to 50 kV.
CFifteen feet is a crane-standard clearance for lines above 50 kV, not the scaffold rule for a 13.8 kV line.
DTwenty feet is the crane standard's planning distance when the voltage is unknown. Here the voltage is known and the scaffold rule applies.
Card 14
A mobile crane will be set up on a tight lot next to a street with overhead distribution lines of unknown voltage. What does OSHA require BEFORE the crane is assembled?
Pick an answer. A short note for each option, A to D, appears here.
ASwing-radius barricades address struck-by hazards and come after setup, not the power line assessment required before assembly.
BTen feet is valid only for lines confirmed at 50 kV or less; with unknown voltage it is not an acceptable starting point.
CCorrect: before assembly, the work zone is identified and checked for whether the crane, load line or load could come within 20 feet of a line.
DLaydown distances matter for logistics but do not address the power line hazard the rule targets.
Card 15
A worker wants to cut the top off an empty 55-gallon drum that held a solvent, to use it as a trash barrel. What should the supervisor require before any cutting torch is used?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: containers that held flammable substances must be thoroughly cleaned, vented and tested before any welding, cutting or heating.
BPlasma cutting still delivers more than enough heat to ignite residual solvent vapor inside the drum.
COdor is an unreliable test, and an open bung alone does not clear the vapor-air mixture inside.
DAn empty drum can hold a vapor-air mixture that explodes more readily than a full one, outdoors or not.
Card 16
A welder working under a hot work permit on the second floor finishes early and wants to continue the same type of welding on the fourth floor. What should the supervisor require before work resumes?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: a hot work permit covers one inspected location, so the fourth floor needs its own inspection and permit before work resumes.
BThe task type is unchanged, but the new floor has its own combustibles and openings that nobody has checked.
CA verbal note on the old form skips the field inspection the new location requires.
DA fire watch helps but does not remove or shield the fourth floor's combustibles, which the permit check covers.
Talking point 05
Cylinders, hoses and the welding area
Oxygen and fuel-gas cylinders turn hot work into a storage question. Under 29 CFR 1926.350(a), cylinders are secured upright, and stored oxygen sits at least 20 feet from fuel-gas cylinders or behind a noncombustible barrier at least 5 feet high with a fire-resistance rating of at least half an hour.
Hoses and torches in use get inspected at the start of each shift, and defective ones come out of service (29 CFR 1926.350(f) and (g)). Suitable fire extinguishing equipment has to be immediately available in the work area and kept ready (1926.352(d)).