Electrical hazards are the #3 cause of industrial worker fatalities in the United States (OSHA). Electrocution accounts for approximately 400 worker deaths per year.
Violation of electrical safety rules at LEO Industrial Services results in immediate removal from electrical work assignments.
| Current (AC) | Effect on Human Body | Risk Level |
|---|---|---|
| 1 mA | Barely perceptible tingle | Low |
| 5 mA | Slight shock — generally not harmful | Low |
| 6–16 mA | "Let-go" threshold — muscle contraction begins; may be unable to release grip | Moderate |
| 17–99 mA | Painful shock; respiratory difficulty; severe muscle contractions | High |
| 100–200 mA | Ventricular fibrillation — typically fatal without immediate defibrillation | FATAL |
| >200 mA | Severe burns, cardiac arrest, tissue destruction; paradoxically may be "shocked out" of VF | EXTREME |
The human body is an electrical conductor with variable resistance. Skin resistance dominates: dry skin ≈ 100,000 Ω, wet skin ≈ 1,000 Ω. Internal body resistance (tissue, blood) is approximately 300–500 Ω.
I = V ÷ R = 120V ÷ 1,000Ω = 120 mA
120 mA is well within the ventricular fibrillation range. Household 120V is potentially lethal under wet conditions.
I = V ÷ R = 480V ÷ 1,000Ω = 480 mA
480 mA causes immediate cardiac arrest and severe burns. 480V three-phase is the most common lethal voltage in industrial settings.
| Contact Type | Description | Common Scenario |
|---|---|---|
| Series (hand-to-hand) | Current enters one hand, travels across the chest/heart, exits the other hand. Crosses the heart — most dangerous path. | Grabbing both sides of a live conductor |
| Series (hand-to-foot) | Current enters hand, travels down through torso and legs to ground. Also crosses the heart. | Standing on a grounded surface while touching an energized part |
| Parallel | Touching an energized conductor while you yourself are grounded — you become a path to ground. | Most common industrial shock scenario |
| Hazard | Mechanism | Outcome |
|---|---|---|
| Shock | Current through the body via direct contact with energized conductor | Burns, cardiac arrest, respiratory failure, death |
| Arc Flash | Sudden release of electrical energy through ionized air — temperatures up to 35,000°F | Burns (1.2 cal/cm² causes second-degree burn), blindness, death |
| Arc Blast | Rapid expansion of vaporized copper and superheated air — pressure waves exceeding 2,000 lbs/ft² | Barotrauma, shrapnel injuries, death. Molten copper travels >700 mph. |
| Fire | Electrical arc ignites surrounding materials; overloaded conductors overheat insulation | Burns, smoke inhalation, facility damage |
Upon completing this lesson, you will be able to:
| Requirement | Code | Status |
|---|---|---|
| Lockout/Tagout Fundamentals | LEO-LOTO-001 | REQUIRED — must be completed first |
| Module 2 Safety Training | LEO-ACE-02 | REQUIRED |
| Hazard Symbol Literacy | LEO-ACE-01-003 | Recommended |
"Only Qualified Electrical Personnel (QEP) may work on or near exposed energized conductors above 50V."
A LEO team member is designated QEP only if they meet all three of the following criteria:
| Criterion | Requirement |
|---|---|
| Training currency | Has completed NFPA 70E training within the last 3 years |
| Licensure or designation | Holds a valid Journeyman or Master Electrician license, OR has been formally designated QEP by LEO management in writing |
| Arc flash PPE training | Has completed arc flash PPE training and is familiar with CAT 0–4 PPE requirements |
Lockout/Tagout for electrical energy has specific requirements beyond mechanical LOTO. Electrical systems may have multiple energy sources, stored energy in capacitors, and the ability to be backfed from secondary sources. Never assume a circuit is de-energized because a breaker is open.
Review the single-line diagram (SLD) for the equipment. Industrial equipment commonly has multiple feeds — primary, control power, UPS backup, and generator circuits. All sources must be identified before any isolation begins. Never assume a single-feed topology.
Inform all workers in the area that electrical LOTO is being applied. This prevents personnel from inadvertently energizing equipment from a remote location or another panel.
Turn the equipment off using its normal stopping procedure first. Then open the main disconnect switch, circuit breaker, or motor controller. Use QEP or trained personnel for this step at voltages above 50V.
Open the disconnect switch to visible-gap isolation, pull fuses from the fuse block, rack out the breaker to the disconnected position, or open the knife switch. A breaker in the OFF position is not isolation — the bus may still be energized.
Attach a lockout hasp to the isolation point and apply your personal padlock. Your lock stays on until you remove it — no supervisor or manager may remove it without following the emergency removal procedure. Apply a DANGER tag with your name, date, and contact information.
Discharge capacitors per manufacturer procedure (often 5–15 minutes of wait time, or active discharge with a resistor). Bleed down UPS systems. Discharge VFD (variable frequency drive) bus capacitors — many VFDs carry 480–800V DC on the bus for minutes after shutdown. Verify motor windings are not acting as generators (coast-down).
Using a calibrated, appropriate-voltage-rated meter or non-contact voltage tester:
(a) Test the meter on a known live source to confirm the meter is functioning.
(b) Test the isolated circuit/terminals to verify zero voltage.
(c) Test the known live source again to confirm the meter did not fail during testing.
All three tests must pass. This is the test-test-test protocol. Skipping any step is a procedural violation.
When work is complete: verify all tools, materials, and personnel are clear. Remove locks in reverse order of application. Notify affected employees. Restore energy in controlled sequence. Document LOTO removal.
An arc flash is a sudden, uncontrolled release of electrical energy through ionized air when the voltage exceeds the dielectric strength of the air gap between conductors. The energy released in milliseconds can be catastrophic:
| Arc Flash Effect | Magnitude | Consequence |
|---|---|---|
| Temperature | Up to 35,000°F (4× the surface temperature of the sun) | Instantaneous severe burns; ignition of all combustibles in the area |
| Pressure wave (Arc Blast) | Can exceed 2,000 lbs/ft² | Ruptures eardrums, throws workers, causes blunt trauma |
| Shrapnel | Molten copper at >700 mph | Penetrating injuries; burns through PPE not rated for the energy level |
| Intense light | UV/IR radiation | Arc eye (welder's flash), permanent retinal damage, temporary blindness |
| Sound | >165 dB | Permanent hearing loss; vestibular damage |
| Boundary | Description | Who May Cross |
|---|---|---|
| Flash Protection Boundary | Outer limit — an unprotected person could receive a curable burn (just at 1.2 cal/cm²) if an arc occurred | Nobody without PPE rated for the arc flash hazard |
| Arc Flash Boundary | Distance within which a worker could receive a second-degree burn (≥1.2 cal/cm²) if an arc occurred | QEP with arc-rated PPE only |
| Limited Approach Boundary | Shock protection boundary — unqualified personnel must stop at this line | QEP only (non-QEP may enter only with escort by QEP and appropriate PPE) |
| Restricted Approach Boundary | Closest to the energized conductor — same risk as touching a conductor ("arc-in-a-box"); accidental contact likely | QEP with full PPE and insulated tools only |
| CAT | Incident Energy | Minimum PPE Required | Typical Scenario |
|---|---|---|---|
| CAT 0 | < 1.2 cal/cm² | Safety glasses, hearing protection, FR (flame-resistant) shirt, leather work gloves | Low-voltage panels, 120V circuits |
| CAT 1 | 1.2 – 4 cal/cm² | CAT 0 + arc-rated FR shirt and pants (4 cal/cm² rating), face shield, hard hat | 240V residential/commercial panels |
| CAT 2 | 4 – 8 cal/cm² | CAT 1 + arc-rated FR jacket, arc flash face shield hood (8 cal/cm²), Class 0 rubber gloves | 480V motor control center (MCC) |
| CAT 3 | 8 – 25 cal/cm² | 25 cal/cm² arc flash suit, arc flash hood, hearing protection, Class 2 rubber gloves | 480V switchgear, industrial distribution |
| CAT 4 | 25 – 40 cal/cm² | 40 cal/cm² arc flash suit, full arc flash hood, leather gloves over Class 2 rubber, hearing protection | Medium voltage switchgear (4–15kV) |
All electrical equipment at LEO job sites must be labeled with arc flash analysis data. A label will show: Nominal Voltage, Arc Flash Boundary distance (in inches or feet), Incident Energy (in cal/cm²), Required PPE Category, and Working Distance assumption. Never open a panel that lacks an arc flash label without first consulting QEP and performing a hazard assessment.
| PPE Item | Standard | When Required | LEO Rule |
|---|---|---|---|
| Insulating rubber gloves (Class 00–4) | ASTM D120 | Any energized electrical work above 50V | QEP required for use. Must be inspected for cuts/punctures and air-tested before every use. Leather protectors worn over gloves for mechanical protection. |
| Arc flash face shield / hood | ANSI Z87.1 / NFPA 70E | Work near energized conductors with arc flash risk | Required for CAT 1 and above. CAT 2+ requires full arc flash hood — a face shield alone is insufficient. |
| FR (flame-resistant) clothing | NFPA 70E / ASTM F1506 | Any arc flash risk present | Required for CAT 0 and above. Must be arc-rated (cal/cm² rating matching or exceeding the hazard). Do NOT wear synthetic fabrics (they melt). |
| Insulating mats and blankets | ASTM D1048 | Working near live bus bars or open energized enclosures | QEP judgment call based on hazard assessment. Must be rated for the voltage class present. |
| Safety glasses | ANSI Z87.1 | Always in electrical work areas | Mandatory. Must be side-shielded in electrical areas. Provide minimal arc flash protection — not a substitute for arc face shield. |
| Voltage-rated (VDE) tools | IEC 60900 | Any electrical work — energized or not | Red-handled IEC 60900 rated tools only at LEO. Standard tools are not insulated and must not be used for electrical work. Never use tools with damaged insulation. |
| Class | Max AC Proof Voltage | Max Working Voltage AC | Color Code |
|---|---|---|---|
| Class 00 | 2,500V AC | 500V AC | Beige |
| Class 0 | 5,000V AC | 1,000V AC | Red |
| Class 1 | 10,000V AC | 7,500V AC | White |
| Class 2 | 20,000V AC | 17,000V AC | Yellow |
| Class 3 | 30,000V AC | 26,500V AC | Green |
| Class 4 | 40,000V AC | 36,000V AC | Orange |
Before every use: (1) Visual inspection — look for cuts, abrasions, punctures, ozone cracking, embedded contaminants. (2) Roll-down air test — roll the cuff to trap air inside, squeeze to pressurize, check for leaks. (3) Check date stamp — rubber gloves must be tested every 6 months per ASTM D120 and are stamped with a test date. Never use expired or damaged gloves.
The "test before touch" rule applies any time you are about to make contact with a terminal, conductor, or electrical component — even after LOTO has been applied. The three-step meter verification protocol (test-test-test) ensures that your measuring instrument is working before and after you use it.
You are about to connect a meter to a terminal block that should be de-energized under LOTO. Click the steps in the correct order to complete the test-before-touch protocol.
| Hazard | Description | Prevention |
|---|---|---|
| Overhead power lines | Often uninsulated distribution lines operating at 4–25kV. The most common cause of fatal electrocution in construction and industrial outdoor work. | Maintain minimum 10-foot clearance for lines up to 50kV. A spotter is required when working equipment (cranes, lifts, ladders) near overhead lines. Call the utility before digging or lifting near lines. |
| Damaged extension cords | Cracked insulation, cut cords, and damaged plugs expose conductors and create shock and fire hazards. Common in industrial environments due to mechanical damage. | GFCI protection required for all outdoor and wet-area use. Inspect cords before every use. Never use a cord with exposed conductors, damaged insulation, or a missing ground pin. Remove from service immediately — do not tape over damage. |
| Improper or missing grounding | Equipment grounding conductors (EGC) provide the fault-current return path that trips breakers during a ground fault. Without grounding, the equipment enclosure becomes energized and shock occurs on contact. | Verify ground continuity before energizing any portable equipment. Use a three-wire (grounded) receptacle tester. Never remove or bypass the ground pin of a plug. |
| Overloaded circuits | Circuits loaded beyond their ampacity cause overheating of conductors and insulation. Overheated insulation fails and creates ground faults or fires. Breakers that repeatedly trip are signaling an overloaded circuit. | Match load to circuit ampacity. Do not bypass OCPs (overcurrent protection) or install higher-rated fuses to "fix" a tripping breaker. Never tape breakers in the ON position — this is a code violation and fire hazard. |
| Wet conditions | Water reduces skin resistance from ~100,000Ω to ~1,000Ω, dramatically increasing the current from a given voltage. Standing water provides a low-resistance path to ground. | GFCI protection is mandatory in wet and damp locations. No electrical work should be performed while standing in water. Ensure hands are dry before operating electrical controls. |
| Working alone | If a worker suffers an electrical shock with no one present, there is no one to call 911, no one to de-energize the source, and no one to start CPR. Alone + electrocuted = death. | Buddy system required for all electrical work at LEO. If a worker cannot be released from grip (muscle lock-up from current), the buddy can de-energize the source rather than trying to pull them free. |
| Capacitor discharge hazard | Capacitors in power supplies, VFDs, motor drives, and UPS systems store electrical energy and retain charge after the main power is removed. A 480V VFD bus capacitor can hold lethal voltage for 5–15 minutes after shutdown. | Follow manufacturer's discharge procedure. Wait the specified minimum time (commonly 5 minutes). Always verify with a meter — never assume discharge is complete because the indicator lights are off. |
| Back-fed circuits | A circuit that appears de-energized at its primary breaker can be energized by a secondary source: a second transformer, a transfer switch, a generator, or a cross-connected neutral. Common in buildings with emergency power systems. | Review the single-line diagram for all energy sources before isolating. Apply LOTO at all sources. Never assume a circuit is dead because one breaker is open. Always test before touch. |
If you grab a person who is being electrocuted, you will also be electrocuted. You become a second victim. The current that is killing them will flow through you. Your first priority is to break the electrical circuit — not to grab the victim.
Determine if the victim is still in contact with the energized source. Look for the source of power. Call out to them — do not run in and grab. If there is any possibility of contact with an energized source, treat them as still connected.
Throw the nearest circuit breaker, pull the disconnect, or push the E-stop. Use one hand only (keeps current from crossing your chest if you accidentally contact voltage). Use insulated tools. Look away from the panel when you operate the switch — arc flash can occur. Do this from the side, not from directly in front.
All electrical injuries require emergency medical evaluation. Even if the victim appears uninjured and is conscious, cardiac monitoring is required for a minimum of 24 hours after electrical contact. Cardiac arrhythmias can occur hours after the event. Do not let a victim "walk it off."
Verify the source is de-energized before approaching the victim. Once confirmed safe, begin CPR if the victim is unresponsive and not breathing. Continue until EMS arrives. Use an AED if available — electrical shock frequently causes ventricular fibrillation, which AEDs are designed to treat.
Cover electrical burns with clean, dry dressing. Do not apply ice, water, or creams to electrical burns. Electrical burns are frequently much deeper than they appear on the surface — internal tissue damage can be severe even when the skin wound looks minor. Inform EMS of entry and exit wound locations.
Contact your LEO supervisor immediately. Do not disturb the scene unless necessary for rescue. Document conditions: what equipment was involved, what work was being performed, whether LOTO was in place, presence of witnesses. An OSHA-recordable incident investigation will follow.
Read each scenario. Identify the primary electrical hazard present. Click your answer for immediate feedback.
| Standard | Title | Key Requirements for LEO Technicians |
|---|---|---|
| 29 CFR 1910.147 | Control of Hazardous Energy (Lockout/Tagout) | Written LOTO program required; all energy sources identified and controlled; employee training; periodic inspections; personal lock requirement; energy verification before work begins |
| 29 CFR 1910.303 | General Electrical — Wiring Design and Protection | Working clearances in front of electrical panels (min. 3 ft for 120–250V, increasing with voltage); guarding of live parts; proper wiring methods; equipment ratings matching the installation |
| 29 CFR 1910.305 | General Electrical — Wiring Methods, Components, and Equipment | Extension cord limitations (not as permanent wiring); GFCI requirements for temporary power; cord condition requirements; strain relief; ampacity matching |
| 29 CFR 1910.333 | Electrical — Safe Work Practices (Energized Work) | Energized work permit requirements; approach distance tables; one-hand rule for panel switching; insulated tools and PPE; qualified worker definition; two-person rule |
| 29 CFR 1910.335 | Safeguards for Personnel Protection | Required PPE for electrical work; insulating protective equipment; non-conductive headgear; face protection; inspection and testing of PPE; prohibited clothing (synthetic fabrics, conductive jewelry) |
| NFPA 70E (2024) | Standard for Electrical Safety in the Workplace | Arc flash risk assessment methodology; PPE categories (CAT 0–4); incident energy analysis; approach boundary definitions; energized electrical work permits; shock and arc flash hazard identification |
OSHA 29 CFR 1910 Subpart S is the regulatory requirement enforced by law. NFPA 70E is a consensus standard developed by industry experts that provides detailed technical guidance on how to comply with OSHA's requirements, particularly for arc flash. OSHA cites NFPA 70E as the authoritative source for arc flash PPE requirements. Both must be followed.
Answer all 5 questions. A score of 4/5 (80%) or higher is required to complete this lesson. Select your answer and click Check.
Click each item to mark it complete. Use before beginning any work in an area with electrical equipment present.