1.4 Electrocution
Electrocution is the Focus Four hazard that gives no warning and leaves no room to react. It takes surprisingly little current through a body to stop a heart, the voltage that does it is ordinary jobsite voltage, and the two situations that kill construction workers most — contact with overhead power lines and contact through damaged cords and tools — are both entirely predictable the day before they happen.
1 Current is what hurts you, not voltage
Voltage pushes; current flows; the current is what does the damage. OSHA's publication Controlling Electrical Hazards (OSHA 3075) sets out what different amounts of current through the body do. The numbers are far smaller than most people expect.
| Current | Reaction |
|---|---|
| 1 milliampere | Faint tingle |
| 5 milliamperes | Slight shock, not painful; the average person can let go, but the involuntary reaction can cause a fall or other injury |
| 6–25 mA (women), 9–30 mA (men) | Painful shock, loss of muscular control — the "let-go" range: the person cannot release the conductor |
| 50–150 milliamperes | Extreme pain, respiratory arrest, severe muscular contraction; death is possible |
| 1,000–4,300 milliamperes | The heart's rhythmic pumping stops; nerve damage; death likely |
A 15-amp circuit breaker protects the wire from overheating. It will happily deliver ten times the lethal current through a person and never trip. That single fact explains why construction sites need ground-fault protection: a breaker protects the building, a GFCI protects the person. A GFCI compares the current going out with the current coming back and shuts off when the difference exceeds about 5 milliamperes — well below the let-go range — in a fraction of a second.
2 Ground-fault protection on construction sites
29 CFR 1926.404(b)(1)(i) gives the employer two choices, and only two: ground-fault circuit interrupters, or a written assured equipment grounding conductor program. These are in addition to normal equipment grounding, not a substitute for it.
The GFCI route (1926.404(b)(1)(ii)) covers all 120-volt, single-phase, 15- and 20-ampere receptacle outlets on construction sites that are not part of the permanent wiring of the building or structure and are in use by employees. In plain terms: the temporary power on the job. Receptacles on a small two-wire portable or vehicle-mounted generator rated at 5 kW or less, with the circuit conductors insulated from the frame and all other grounded surfaces, are excepted.
The assured grounding route (1926.404(b)(1)(iii)) is real work, which is why most contractors choose GFCIs. It requires a written description of the program available on the jobsite, one or more designated competent persons to run it, a visual inspection of every cord set, plug, cap, receptacle and cord-connected tool before each day's use, continuity testing of all equipment grounding conductors, and terminal testing of every receptacle and plug — performed before first use, after repairs, after any incident that could have caused damage such as a cord being run over, and at intervals not exceeding three months (six months for fixed cord sets and receptacles not exposed to damage). Equipment that has not met these requirements may not be made available for use.
3 Cords, plugs and tools
Damaged flexible cords are the everyday version of this hazard. 29 CFR 1926.416(e)(1) is one sentence: worn or frayed electric cords or cables shall not be used. Paragraph (e)(2) adds that extension cords shall not be fastened with staples, hung from nails, or suspended by wire. And 1926.416(b)(2) requires working spaces, walkways and similar locations to be kept clear of cords so they do not create a hazard — a rule that is as much about trips as about shocks.
Double-insulated tools carry a square-within-a-square symbol and have no ground pin by design; they are not defective. A three-prong tool with the ground pin snapped off is defective, and the "adapter" someone made by cutting off the pin is how a tool housing becomes energized. Tag it and take it out of service — 1926.404(b)(1)(iii)(C) already says equipment found damaged or defective shall not be used until repaired.
4 Working near energized circuits
The general rule is 29 CFR 1926.416(a)(1): no employer shall permit an employee to work in such proximity to any part of an electric power circuit that the employee could contact it in the course of work, unless the employee is protected against shock by de-energizing the circuit and grounding it, or by guarding it effectively by insulation or other means.
Before work begins, 1926.416(a)(3) requires the employer to find out — by inquiry, direct observation, or instruments — whether any part of an energized circuit, exposed or concealed, is located where the work could bring a person, tool, or machine into physical or electrical contact with it; to post and maintain warning signs where such a circuit exists; and to advise employees of the location, the hazards, and the protective measures. Where the exact location of underground power lines is unknown, 1926.416(a)(2) requires insulated protective gloves for employees using jackhammers, bars, or other hand tools that could contact a line.
Overhead lines deserve their own habit, because they are the ones that kill people who never touched anything electrical. Scaffold frames, aluminum ladders, drywall sheets in the wind, mast climbers, dump bodies and boom tips have all made contact. For cranes and derricks, 1926.1408(a)(2) sets a 20-foot minimum clearance up to 350 kV unless the line is confirmed de-energized and visibly grounded or the smaller Table A distances are used with the required precautions. Treat every overhead conductor as energized and bare until a utility representative tells you otherwise in person.
5 De-energizing, tagging and verifying
When a circuit is taken out of service for work, 29 CFR 1926.417 requires three things. Controls that are to be deactivated during work on energized or de-energized equipment or circuits shall be tagged. Equipment or circuits that are de-energized shall be rendered inoperative and shall have tags attached at all points where they could be energized. And tags shall be placed so as to identify plainly the equipment or circuits being worked on.
General industry work under 29 CFR 1910.147 — the Control of Hazardous Energy standard, the fourth most cited standard in the country — goes further, with machine-specific written procedures, individual locks, and a mandatory verification step. Whichever standard applies to your work, the sequence that keeps people alive is the same:
- 1Identify every energy source feeding the equipment, including back-feeds, generators and stored energy in capacitors.
- 2Notify everyone affected before anything is shut down.
- 3Open the disconnect, then lock and tag it at every point where the circuit could be re-energized.
- 4Test before touch: verify absence of voltage with a meter you have just proved on a known live source, then proved again afterwards.
- 5Ground where required, and treat anything not verified as still live.
- 6Restore only after tools are clear, guards are back, and everyone affected has been told.
6 If someone is being shocked
Do not touch them. A person in the let-go range is a conductor, and the second victim in an electrocution is almost always the rescuer. De-energize the source if you can reach a disconnect or a plug. If the contact involves overhead lines and a piece of equipment, keep everyone back — the ground around a downed conductor can carry a lethal voltage gradient, and an operator inside the machine is usually safest staying put until the utility confirms the line is dead.
Call 911 immediately, and start CPR once the person is clear of the circuit and it is safe to touch them. Every electrical contact, even one that "just stung," goes to medical evaluation: current that crosses the chest can cause a heart rhythm problem that shows up later, and burns from current travel are internal and far larger than the entry mark suggests.
- Current kills, not voltage: 6–30 mA is already the let-go range, and 50–150 mA can stop breathing (OSHA 3075). A 15-amp breaker will never protect a person.
- 1926.404(b)(1): construction sites must use GFCIs on non-permanent 120 V, 15/20 A receptacles, or run a written assured equipment grounding conductor program with daily visual checks and testing at least every three months.
- 1926.416(e): worn or frayed cords may not be used; extension cords may not be stapled, nailed up, or hung by wire.
- 1926.416(a)(1): work near an energized circuit only after de-energizing and grounding it, or effectively guarding it by insulation or other means; 1926.416(a)(3) requires the employer to check for concealed circuits, post signs, and brief the crew.
- Treat every overhead line as energized and bare; 20 feet of clearance for cranes up to 350 kV under 1926.1408(a)(2).
- Tag controls and de-energized circuits under 1926.417, and always test for absence of voltage with a meter you have proved before and after.
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.