OSHA Safety Certification / OSHA 10 / OSHA 30 / NFPA 70E: Focus Four - Electrocution

Electrocution Hazards (OSHA 1910.333 / 1926.416 / NFPA 70E)

Audience: working professional / trade certification candidate

Electrocution is one of OSHA's Focus Four fatal hazards — electrical injuries range from tingle to cardiac arrest depending on current magnitude, and prevention requires understanding shock physiology, the BE SAFE hazard categories, LOTO procedures, protective devices, and NFPA 70E approach boundaries.

Key Points

• Electrical shock occurs when a person BECOMES PART of an electrical circuit.
• It is CURRENT (milliamps), not voltage alone, that determines injury severity.
• 1 mA = faint tingle; 5 mA = slight shock with fall risk; 6–30 mA = freeze zone (cannot let go); 50–150 mA = respiratory arrest, death possible; 10,000 mA = cardiac arrest, death probable.
• 15,000 mA (15 amps) = lowest overcurrent at which a typical fuse or circuit breaker opens.
• BE SAFE electrical hazards: Burns, Explosions, Shock, Arc Flash, Fire, Electrocution.
• Arc flash releases thermal energy, acoustic energy, and pressure waves — can cause severe burns without contact.
• GFCI detects current leakage as small as 5 mA and cuts off power — required near water sources.
• LOTO (Lockout/Tagout): mandatory before servicing energized equipment — each worker applies their own lock.
• Tags alone (Tagout only) are permitted only when equipment cannot accept a lock — must be equally effective.
• NFPA 70E defines four approach boundaries: Flash Protection, Limited, Restricted, and Prohibited.
• Only Qualified Persons may cross the Restricted Approach Boundary.
• PPE category (1–4) is determined by incident energy analysis or arc flash PPE category tables.
• Sweat, wet conditions, and broken skin all INCREASE shock injury risk.
• Pulling a cord (not the plug) to disconnect is UNSAFE — damages insulation.
• Attaching tags to equipment while workers are exposed to live parts is required by OSHA.

Why It Matters: Electrocution is the 4th leading cause of workplace fatalities in construction. OSHA and NFPA 70E are the two most cited standards in electrical safety compliance — inspectors specifically look for missing LOTO programs, absent GFCI protection, and workers without arc flash PPE. Exam writers exploit the milliamp table and LOTO sequence because workers consistently underestimate low-voltage hazards and skip procedural steps under time pressure.

Terms To Remember

Electrical Shock

Reflex response when electrical current passes through the human body; occurs when person becomes part of a circuit.

Arc Flash

Release of energy from an electric arc — thermal, acoustic, and pressure waves; can cause burns without direct contact.

Arc Blast

Pressure wave component of an arc flash event; can cause physical trauma and hearing damage.

Ground Fault

Unintended current path to ground; detected by GFCI.

GFCI (Ground Fault Circuit Interrupter)

Detects current leakage (~5 mA) and cuts off power within milliseconds.

AFCI (Arc Fault Circuit Interrupter)

Detects arc faults in wiring (series arcs) that can cause fires; required in residential sleeping areas and more.

Lockout/Tagout (LOTO)

Safety procedure: de-energize, lock, and tag equipment before servicing to prevent accidental energization.

Lockout Device

Physical lock applied to energy-isolating device; prevents re-energization.

Tagout Device

Warning tag attached to energy-isolating device when lockout is not possible; must be equally effective.

Energy-Isolating Device

Mechanical device that physically prevents transmission of energy (breaker, valve, disconnect).

Authorized Employee

Worker who applies the lockout/tagout device.

Affected Employee

Worker whose job requires operating equipment subject to LOTO.

Qualified Person (NFPA 70E)

Trained and knowledgeable in construction/operation of electrical equipment; recognizes hazards.

Unqualified Person

Worker with little or no training in electrical hazards; must stay outside Limited Approach Boundary.

Flash Protection Boundary

Outermost NFPA 70E boundary; point at which a person could receive a 2nd degree burn (1.2 cal/cm²) from an arc flash.

Limited Approach Boundary

Unqualified persons must not cross without escort by qualified person.

Restricted Approach Boundary

Only qualified persons wearing appropriate PPE may cross.

Prohibited Approach Boundary

Same risk as direct contact with energized conductor; special NFPA 70E requirements apply.

Incident Energy

Amount of energy impressed on a surface at a given distance from an arc fault; measured in cal/cm².

PPE Category (Arc Flash)

NFPA 70E category 1–4 determining minimum arc-rated PPE required based on incident energy.

Energized Electrical Work Permit

NFPA 70E document required before performing justified energized work; documents hazard analysis and PPE.

Step Process Formula

Title: Two Core Skills: LOTO Full Sequence + NFPA 70E Approach Boundary Determination — Side-by-Side

Milliamp Effects Table

Title: Current Effects on the Human Body — Exam-Critical Values

Rows

Current: 1 mA

Effect: Faint tingle — barely perceptible.

Current: 5 mA

Effect: Slight shock; not painful; strong involuntary movements can cause fall injury. Most can 'let go.'

Current: 6–25 mA (women)

Effect: Painful shock; muscular control lost; 'freeze current' zone begins — may not be able to let go.

Current: 9–30 mA (men)

Effect: Same freeze zone; nerve damage begins; loss of muscle control confirmed.

Current: 50–150 mA

Effect: Extremely painful; respiratory arrest (breathing stops); heart fibrillation possible; DEATH POSSIBLE.

Current: 1,000–4,300 mA

Effect: Heart's rhythmic pumping ceases; muscular contraction; severe nerve damage; DEATH LIKELY.

Current: 10,000 mA (10 A)

Effect: Cardiac arrest; severe burns; DEATH PROBABLE.

Current: 15,000 mA (15 A)

Effect: Lowest overcurrent at which a typical fuse or circuit breaker opens a circuit.

Key Exam Facts

• Voltage does NOT determine injury severity alone — current through the body does.
• Body resistance varies: dry skin ~100,000 Ω; wet/sweaty skin ~1,000 Ω — sweat dramatically INCREASES current and injury risk.
• A standard 120V circuit can deliver lethal current through a low-resistance path.
• GFCI trips at ~5 mA — designed to prevent electrocution before freeze current is reached.
• A standard 15A circuit breaker does NOT protect against electrocution — it opens at 15,000 mA, far above lethal levels.

Be Safe Hazards

Title: BE SAFE — Six Major Electrical Hazards

Hazards

Letter: B

Hazard: Burns

Description: Caused by electricity passing through tissues, high temperatures from an explosion, or overheated equipment. Most common electrical injury.

Types: Electrical burns (current through tissue), arc burns (radiant heat), thermal burns (from fires ignited by electricity).

Letter: E

Hazard: Explosions

Description: Electrical arcs can ignite flammable vapors, gases, or dust in the work environment, causing explosions.

Prevention: Use intrinsically safe equipment in hazardous locations; control ignition sources.

Letter: S

Hazard: Shock

Description: Occurs when a person becomes part of an electrical circuit. Severity depends on current magnitude, path through body, and duration.

Risk Factors: Sweat, wet conditions, broken skin, contact area, and current path (hand-to-hand vs. hand-to-foot).

Letter: A

Hazard: Arc Flash

Description: Release of energy from an electric arc — thermal energy, acoustic energy, and pressure waves. Can cause severe burns, blindness, and injury WITHOUT direct contact.

Source Example: Circuit breaker box, bus bars, switchgear, panel work.

Protection: Arc-rated PPE, face shield, and maintaining safe approach boundaries per NFPA 70E.

Letter: F

Hazard: Fire

Description: Electrical faults, overloaded circuits, and faulty wiring can ignite materials and cause fires.

Prevention: Proper conductor sizing, overcurrent protection, and AFCI breakers in required locations.

Letter: E

Hazard: Electrocution

Description: Fatal electric shock. In almost all cases, touching power lines or energized sources results in severe injury or death.

Key Fact: Direct contact with overhead power lines or energized conductors is nearly always fatal.

Part A LOTO Procedure

Label: Part A — Lockout/Tagout (LOTO) Full Procedure Sequence

Standard: OSHA 29 CFR 1910.147 (General Industry) / 1926.417 (Construction)

Purpose: Protect workers from unexpected energization, startup, or release of stored energy during servicing or maintenance.

LOTO Steps In Order

1 — Prepare for shutdown

Action: Identify ALL energy sources (electrical, pneumatic, hydraulic, thermal, gravitational, chemical). Identify energy-isolating devices for each source. Obtain correct locks and tags.

2 — Notify affected employees

Action: Inform all affected employees that LOTO is being applied and the reason why. They must not attempt to restart the equipment.

3 — Equipment shutdown

Action: Follow established shutdown procedure to bring equipment to a complete stop using normal stopping methods.

4 — Isolate energy sources

Action: Operate all energy-isolating devices (circuit breakers, disconnects, valves) to the OFF or SAFE position. Isolate ALL energy sources — not just electrical.

5 — Apply lockout/tagout devices

Action: Each authorized employee applies their PERSONAL lock to each energy-isolating device. If multiple workers are servicing, each applies their OWN lock. Apply a tag identifying the worker, reason, and date. If equipment cannot accept a lock, tagout only — must be equally effective.

6 — Release/restrain stored energy

Action: Discharge all stored energy: bleed pneumatic/hydraulic lines, discharge capacitors, block gravity loads (lowered or blocked), relieve spring tension, allow thermal cooling.

7 — Verify isolation (ZERO ENERGY STATE)

Action: Attempt to start equipment using normal start controls — machine must NOT start. Use a calibrated voltmeter or test instrument to verify zero voltage at all test points. This step is MANDATORY — never assume.

Restoration Steps

• Ensure all tools, materials, and non-essential items are removed from the work area.
• Verify all workers are safely positioned away from equipment.
• Each authorized employee removes their OWN lock and tag.
• Notify affected employees that LOTO is being removed.
• Restore energy sources and verify safe startup.

Critical LOTO Rules

• Each worker applies their OWN lock — never use someone else's lock.
• Keep the ONLY key with you — never leave it with supervisor or in lock box accessible to others.
• Tags alone are only permitted when physical lockout is impossible — must be equally effective, must state 'Do Not Energize.'
• Multiple energy sources require a lock on EACH isolating device.
• Lockout devices must be substantial enough to prevent removal without excessive force.
• OSHA requires a written LOTO program; annual inspections of procedures; and training of all authorized and affected employees.
• Attach tags to identify equipment being worked on whenever any worker is exposed to live parts.
• Group lockout (hasp device) allows multiple workers to each add their own lock to a single hasp.

Worked Scenario

Scenario: An HVAC technician is replacing a contactor in a rooftop unit. What is the correct LOTO sequence?

Steps

• Step 1 — Identify energy sources: 240V electrical supply at disconnect + capacitors in unit.
• Step 2 — Notify building maintenance that RTU will be de-energized.
• Step 3 — Set thermostat to OFF; verify unit is not running.
• Step 4 — Open the unit's disconnect switch to the OFF position.
• Step 5 — Apply personal lock to the disconnect; attach tag with name, date, reason.
• Step 6 — Discharge run and start capacitors using a 15,000–20,000 Ω resistor before touching.
• Step 7 — Verify with voltmeter: measure L1–L2, L1–ground, L2–ground at contactor terminals = 0V before proceeding.

Part B NFPA 70e Boundaries

Label: Part B — NFPA 70E Approach Boundaries & PPE Categories

Standard: NFPA 70E — Standard for Electrical Safety in the Workplace

Purpose: Establish safe work practices and PPE requirements for work on or near energized electrical equipment.

Approach Boundaries

Overview: NFPA 70E defines concentric boundaries around energized equipment. Moving closer requires more training, PPE, and justification.

Boundaries

Boundary: Flash Protection Boundary (Arc Flash Boundary)

Description: Outermost boundary. A worker at this distance could receive a just-curable 2nd degree burn (1.2 cal/cm²) if an arc flash occurs without PPE.

Who Can Cross: Anyone — but arc flash PPE must be worn when crossing.

Distance: Calculated from incident energy analysis or NFPA 70E tables (varies by equipment and voltage).

Boundary: Limited Approach Boundary

Description: Shock protection boundary for unqualified persons.

Who Can Cross: Unqualified persons may cross ONLY if accompanied and continuously escorted by a qualified person.

Distance: Varies by voltage; for 120–240V typically ~3 ft 6 in.

Boundary: Restricted Approach Boundary

Description: Increased shock hazard zone.

Who Can Cross: ONLY qualified persons wearing appropriate shock protection PPE.

Requirement: Qualified person must have an Energized Electrical Work Permit for justified energized work.

Distance: Varies by voltage; for 120–240V typically ~1 ft.

Boundary: Prohibited Approach Boundary

Description: Same risk as direct contact with energized conductor.

Who Can Cross: Only with special written approval, insulated tools rated for the voltage, and full PPE.

Distance: Extremely close — varies by voltage; essentially at the conductor surface for low voltage.

Arc Flash PPE Categories

Title: NFPA 70E Arc Flash PPE Categories (Table Method)

Note: When incident energy analysis is not performed, NFPA 70E Table 130.7(C)(15) assigns PPE categories based on equipment type and fault current.

Categories

PPE Category 1

Minimum Arc Rating: 4 cal/cm²

Typical Tasks: Working on 120V branch circuits, lighting panels with limited available fault current.

Minimum PPE: Arc-rated shirt and pants or coverall; arc-rated face shield or arc flash suit hood; hard hat; safety glasses; hearing protection; leather gloves.

PPE Category 2

Minimum Arc Rating: 8 cal/cm²

Typical Tasks: 240V panelboards, motor control centers at lower fault levels.

Minimum PPE: Arc-rated shirt and pants or coverall; arc-rated face shield (8 cal rated) or arc flash suit hood; hard hat; safety glasses; hearing protection; leather gloves.

PPE Category 3

Minimum Arc Rating: 25 cal/cm²

Typical Tasks: Switchgear up to 600V at higher fault levels.

Minimum PPE: Arc-rated jacket, pants, shirt, and hood (full arc flash suit); hard hat; safety glasses; hearing protection; leather gloves.

PPE Category 4

Minimum Arc Rating: 40 cal/cm²

Typical Tasks: High-fault-current switchgear and bus work.

Minimum PPE: Full arc flash suit rated ≥40 cal/cm²; hard hat; safety glasses; hearing protection; leather gloves.

Key Rule: The incident energy analysis method always takes precedence over the table method when available. PPE must meet or exceed the calculated incident energy at the work distance.

Worked Scenario

Scenario: A qualified electrician needs to take voltage measurements inside a 480V MCC (Motor Control Center) while it is energized. What boundaries apply and what PPE is required?

Steps

• Step 1 — Identify: 480V energized MCC — qualified person work only.
• Step 2 — Determine if energized work is justified: NFPA 70E requires an Energized Electrical Work Permit documenting why de-energizing creates greater hazard or is infeasible.
• Step 3 — Establish Flash Protection Boundary: calculate from arc flash study or use NFPA 70E tables for 480V MCC — typically 4–10 ft depending on available fault current.
• Step 4 — Select PPE category: 480V MCC with available fault current — typically PPE Category 2 or 3 (8–25 cal/cm²). Verify with arc flash label on equipment.
• Step 5 — Don PPE before crossing Flash Protection Boundary: arc-rated suit matching cal/cm² rating, arc-rated face shield/hood, hard hat, safety glasses, hearing protection, insulated leather gloves rated for 480V.
• Step 6 — Only qualified person crosses Restricted Approach Boundary to take measurements.
• Step 7 — Use appropriately rated CAT III/IV test equipment and insulated probes for 480V work.

Energized Work Justification

Default Rule: De-energizing is ALWAYS the preferred method. Energized work must be justified.

Permitted When

• De-energizing creates a greater hazard (e.g., loss of life support equipment).
• De-energizing is infeasible due to equipment design or operational limitations.
• Qualified person is performing diagnostics, testing, or measurements that require the circuit to be energized.

Required Documentation: Energized Electrical Work Permit — documents hazard analysis, justification, PPE required, and worker acknowledgment.

GFCI AFCI Reference

Title: GFCI, AFCI & Protective Devices — Rules & Locations

GFCI

Function: Detects current leakage to ground at approximately 5 mA and cuts off power within 1/40th of a second — before freeze current is reached.

Required Locations Construction 1926

• All 120V, single-phase, 15A and 20A receptacle outlets at construction sites.
• Temporary wiring installations.
• Any location where water or moisture is present.

Required Locations General Industry 1910

• Bathrooms.
• Kitchens within 6 ft of a sink.
• Outdoors.
• Garages and accessory buildings.
• Crawl spaces and unfinished basements.
• Boat houses and near swimming pools/spas.
• Within 6 ft of any sink in any occupancy.

How It Protects: Continuously compares current leaving on hot wire vs. returning on neutral. A difference of ~5 mA indicates current is leaking through an unintended path (a person) — immediately opens circuit.

Limitation: Does NOT protect against line-to-line shock (both hot wires) — only line-to-ground faults.

AFCI

Function: Detects arc faults in wiring — damaged, overloaded, or loose wiring that creates intermittent arcs capable of igniting fires.

Required Locations Nec 2023

• All 120V, 15A and 20A branch circuits supplying outlets in dwelling unit bedrooms, family rooms, dining rooms, living rooms, parlors, libraries, dens, sunrooms, recreation rooms, closets, hallways, laundry areas, and similar rooms.

Difference From GFCI: AFCI prevents FIRES from arc faults in wiring; GFCI prevents ELECTROCUTION from ground faults. Both can be combined in dual-function AFCI/GFCI breakers.

Ground Fault Vs Overcurrent

Standard Breaker: Protects conductors from overload and short circuit — trips at rated amperage (15A breaker at ~15,000 mA). Does NOT protect against electrocution.

GFCI: Protects people from ground faults — trips at ~5 mA. Does NOT protect conductors from overload.

Key Exam Fact: A 15A breaker provides ZERO protection against fatal electrocution — fatal current (50–150 mA) is far below the breaker's trip point.

Common Confusions

• Students confuse voltage with current as the primary injury factor because 'high voltage' sounds more dangerous — it is CURRENT through the body that determines injury severity; a 120V circuit can deliver lethal current through a low-resistance path (wet skin); sweat drops skin resistance from ~100,000 Ω to ~1,000 Ω, multiplying current by 100x at the same voltage.
• Students confuse tagout as equivalent to lockout because both are 'LOTO' — lockout physically prevents re-energization with a lock; tagout is only a warning tag and is permitted ONLY when the energy-isolating device cannot accept a lock; tagout must be supplemented by additional measures to make it equally effective.
• Students confuse the Flash Protection Boundary with the Restricted Approach Boundary because both are 'danger zones' — the Flash Protection Boundary is the outermost arc flash burn protection line (anyone crossing needs arc PPE); the Restricted Approach Boundary is a closer shock protection line only qualified persons may cross; they address different hazards (arc flash vs. shock).
• Students confuse GFCI with AFCI because both are circuit interrupters — GFCI detects ground faults (current leaking to ground) and protects PEOPLE from electrocution; AFCI detects arc faults in wiring and protects PROPERTY from fires; a standard breaker protects neither people nor property from these hazards — only conductors from overload.

Quick Questions

A worker receives 75 mA of current through their body. What physiological effects should be expected?

Correct Answer: 75 mA falls in the 50–150 mA range: extremely painful shock, respiratory arrest (breathing stops), severe muscle reactions, and heart fibrillation is possible — death is possible at this level. This is well above the 6–30 mA freeze current zone where the worker cannot let go, and well above the 5 mA GFCI trip threshold. A standard 15A circuit breaker provides no protection at 75 mA — it won't trip until 15,000 mA.

During a LOTO procedure, a second technician arrives to assist with the repair. What must happen before they begin work?

Correct Answer: The second technician must apply their OWN personal lock to each energy-isolating device (using a hasp if needed to accommodate multiple locks). Each worker must have personal control of the lock that protects them — one person's lock does not protect another worker. The second technician must also verify zero energy state independently. Only when their own lock is applied may they begin work.

An unqualified worker needs to be in a room where a qualified electrician is performing energized panel work. What boundaries govern the unqualified worker's position?

Correct Answer: The unqualified worker must stay outside the Limited Approach Boundary unless continuously escorted by the qualified person. The unqualified worker must never cross the Restricted Approach Boundary under any circumstances — only qualified persons wearing appropriate PPE may cross that boundary. If the unqualified worker must cross the Flash Protection Boundary for any reason, they must wear arc-rated PPE appropriate to the incident energy at that location.

Exam Answer Frame

Style: 5-mark

Question: Explain why a standard 15-amp circuit breaker does NOT protect workers from electrocution, and describe TWO protective devices that do provide protection against electrical injury to people.

Model Answer: A standard 15-amp circuit breaker is designed to protect CONDUCTORS from overload and short circuit — it opens the circuit at approximately 15,000 milliamps (15 amps). Fatal electrocution occurs at 50–150 mA (respiratory arrest, heart fibrillation) — a current level 100 times lower than the breaker's trip point. The breaker will never open in response to a lethal current flowing through a human body.

Two devices that do protect people: (1) GFCI (Ground Fault Circuit Interrupter) — continuously monitors current balance between the hot and neutral conductors; when a difference of approximately 5 mA is detected (indicating current leaking through a person to ground), the GFCI opens the circuit within 1/40th of a second — before freeze current is reached and before respiratory arrest can occur. Required at all construction site receptacles and near water sources in general industry. (2) Lockout/Tagout (LOTO) — eliminates the electrical hazard entirely by de-energizing the circuit and applying a physical lock that prevents re-energization while workers are exposed. LOTO does not limit the hazard — it removes it. OSHA 1910.147 requires a written LOTO program, trained authorized and affected employees, and verification of zero energy state before work begins.