1.1 Shock, arc and blast: three different injuries
Electricity does not injure people one way. It injures them three ways, and the three arrive by different routes, need different distances and are prevented by different things. Confusing them is why crews think a rubber glove covers everything, or that a closed panel door is nothing to walk past. In 2022, exposure to electricity killed 62 construction workers — 5.7% of all construction deaths that year, the fifth leading cause (BLS Census of Fatal Occupational Injuries, published in CPWR's July 2024 Data Bulletin).
1 Three injuries, one hazard
The Occupational Safety and Health Act does not have a paragraph called "electricity". What it has is 29 CFR 1926 Subpart K for construction and 29 CFR 1910 Subpart S for general industry, and both of them exist because of three physical events: shock, when current passes through a body; arc, when current jumps through the air and releases heat and light; and blast, the pressure wave and flying material that a large arc produces. OSHA's own booklet on electrical hazards states the range plainly: electricity exposes employees to "electric shock, electrocution, burns, fires, and explosions" (OSHA 3075).
Shock requires contact — your body has to become part of the circuit. Arc and blast do not. That single difference explains most of what follows in this course, including why an unqualified person is kept at a distance from equipment that nobody is going to touch.
2 Shock: your body completes the circuit
Electricity travels in closed circuits, normally through a conductor. A shock happens when a person's body — an efficient conductor — mistakenly becomes part of that circuit. OSHA 3075 lists the four ways it happens: contact with both wires of a circuit; contact with one wire of an energized circuit and the ground; contact with a metal part that has accidentally become energized, for example through a break in its insulation; or contact with another conductor carrying current.
The third one is the quiet killer on a jobsite. Nobody plans to touch a conductor. People plan to pick up a drill, hold a light, lean on a machine frame. When insulation fails inside a tool, the metal case becomes the energized part, and the equipment grounding conductor — the third prong — is what is supposed to carry that fault current away instead of through you. 29 CFR 1926.404(f)(6) puts the requirement in one line: the path to ground from circuits, equipment and enclosures shall be permanent and continuous.
3 Arc: the air becomes a conductor
Air is normally an insulator. OSHA 3075 notes the exception directly: even air "can become a conductor, as occurs during an arc or lightning stroke." When a fault develops between conductors — a dropped tool, a loose part, a probe in the wrong place, a rodent — current crosses the gap and the air itself carries it, at temperatures far above anything a jobsite otherwise produces.
The injury that follows is not a shock. OSHA calls it an arc or flash burn, and defines it as resulting "from high temperatures caused by an electric arc or explosion near the body". Near. There is no requirement that anything touch you. That is why the boundary around a person working on open energized equipment is drawn in feet rather than inches, and why the answer to "can I just stand here and watch" is no.
There is a third burn in the same list, and it catches people who think they escaped: the thermal contact burn, from touching hot conductors or conduit — or from clothing catching fire, "as may occur when an electric arc is produced" (OSHA 3075). Your shirt is part of the exposure. Chapter 3 of Part 4 comes back to that.
4 Blast: pressure, sound and flying metal
A large arc does mechanical damage as well as thermal damage. OSHA 3075: "Extremely high-energy arcs can damage equipment, causing fragmented metal to fly in all directions." The conductors and the enclosure vaporize and expand; what leaves the cabinet is metal, molten and solid, moving fast. The same paragraph adds a second warning that matters in refineries, grain handling and paint booths: "even low-energy arcs can cause violent explosions in atmospheres that contain flammable gases, vapors, or combustible dusts."
This is the hazard that 29 CFR 1910.335(a)(1)(v) addresses when it requires eye or face protection "wherever there is danger of injury to the eyes or face from electric arcs or flashes or from flying objects resulting from electrical explosion." Note the phrasing: the standard names flying objects from an electrical explosion as a distinct hazard from the flash itself.
5 Where each one comes from, and what stops it
| Injury | How it reaches you | What the standards put in the way |
|---|---|---|
| Shock / electrocution | Contact — your body closes the circuit | Deenergizing (1910.333(a)(1)), guarding of live parts (1926.403(i)), grounding and the continuous path to ground (1926.404(f)(6)), GFCI or an assured grounding program (1926.404(b)(1)), insulation, insulated tools (1910.335(a)(2)) |
| Arc / flash burn | Radiated heat and light, no contact needed | Distance and access control: only qualified persons on energized parts (1910.333(c)(2)), signs, barricades and attendants (1910.335(b)), eye and face protection (1910.335(a)(1)(v)), and for power generation, transmission and distribution work the arc-rated clothing rules of 1910.269(l)(8) |
| Blast | Pressure wave, sound, molten and solid fragments | The same distance and access controls, plus enclosures kept closed and equipment maintained; face protection against flying objects from electrical explosion (1910.335(a)(1)(v)) |
Read the middle column again. Shock is prevented mostly by things you can install — a ground, a GFCI, an enclosure. Arc and blast are prevented mostly by who is where. That is the shape of this whole course.
6 Why "it's only 120 volts" is the wrong sentence
The most persistent belief on a jobsite is that ordinary building voltage is not really dangerous. The data says otherwise. Of nonfatal direct-contact electrical injuries in construction between 2011 and 2019, only 15.1% involved more than 220 volts (BLS Survey of Occupational Injuries and Illnesses, in CPWR's November 2022 Data Bulletin) — the rest happened at the voltage in every receptacle on site. High voltage dominates the fatal indirect contacts, the boom-into-a-line events; ordinary voltage dominates the injuries that happen to everybody else.
OSHA states the principle in a single sentence worth memorizing: "Low voltage does not imply low hazard" (OSHA 3075). The reason is in the next chapter — a shock that will not let go lasts longer, and duration is one of the four things that decide what a current does to a body.
7 The two standards you will hear quoted, and which one applies
Electrical requirements live in two different places in 29 CFR, and crews mix them up constantly. Construction work is governed by 1926 Subpart K, which runs from 1926.400 to 1926.449 and is split between installation safety requirements (1926.403 to 1926.408) and safety-related work practices (1926.416 and 1926.417). General industry is governed by 1910 Subpart S, whose design rules sit at 1910.303 to 1910.308 and whose safety-related work practices sit at 1910.331 to 1910.335.
The two overlap heavily and differ in a few places that matter. Construction has the ground-fault protection choice of 1926.404(b)(1) — GFCIs or an assured equipment grounding conductor program — which general industry does not. General industry has the detailed energized-work regime of 1910.333, which construction states far more briefly in 1926.416 and 1926.417. And the inspection intervals differ in wording: before each day's use on a construction site, before use on any shift in general industry.
Where does that leave a maintenance technician in a plant who is repairing a wall? OSHA decides by the nature of the work rather than by the type of employer: construction work — construction, alteration and repair, including painting and decorating — falls under Part 1926 while it is going on. This course flags which standard each requirement comes from, every time.
- Electricity injures three ways: shock (contact), arc (radiated heat, no contact) and blast (pressure and flying metal).
- A shock happens when your body closes a circuit — most often through a metal part that became energized, not through a bare wire.
- 29 CFR 1926.404(f)(6) requires the path to ground to be permanent and continuous; that path is what is supposed to carry a fault instead of you.
- OSHA defines an arc or flash burn as coming from high temperatures near the body — proximity is the exposure, and 1910.335(a)(1)(v) requires eye and face protection against arcs and against flying objects from an electrical explosion.
- Shock is largely stopped by hardware; arc and blast are largely stopped by who is allowed where.
- Exposure to electricity killed 62 construction workers in 2022 (5.7% of construction deaths), and most nonfatal direct-contact injuries happen at 220 volts or less. Low voltage does not imply low hazard.
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.