Shock Hazard Analysis
What It Is & How It Works
Electricity remains one of the deadliest hazards in the workplace. In 2023, 147 U.S. workers died from exposure to electricity, a slight increase over the 145 deaths the year before. A shock hazard analysis is one of the core tools used to prevent those deaths, and it is a requirement under the standard most safety programs follow. This guide explains what a shock hazard analysis is, the voltage and current thresholds that drive it, how the process works, and how it pairs with an arc flash hazard analysis.
What Is a Shock Hazard Analysis?
A shock hazard analysis, formally called an electric shock risk assessment in NFPA 70E Article 130.4, is a structured evaluation that determines whether a worker faces a risk of electric shock during a task, how likely and severe that shock could be, and what protective measures are needed to control it. It answers three practical questions: Is a shock hazard present? How close can a person safely approach? And what protection is required to cross that distance?
The analysis applies whenever workers approach exposed energized electrical conductors or circuit parts. Importantly, it is independent of any arc flash evaluation. A shock hazard analysis focuses on voltage potential and direct contact, while an arc flash analysis addresses thermal energy. Both can be required for the same task, but each is assessed separately.
The 2024 edition of NFPA 70E raised the bar further by requiring a thorough risk assessment for every electrical job, not just high-risk tasks. That makes understanding the shock hazard analysis essential for anyone working on or near energized equipment.
Why Voltage and Current Both Matter
People often assume that voltage alone determines danger. In reality, it is the current passing through the body, combined with the path and duration, that injures or kills.
Voltage matters because it drives current across the body’s resistance, but that resistance varies widely, from less than 500 ohms for wet or damaged skin to over 100,000 ohms for dry, intact skin.
Because Ohm’s Law (I = E/R) governs current flow, the same voltage can produce dramatically different outcomes depending on skin condition, contact area, and environmental conditions. The thresholds that define real harm are measured in milliamps.
The 50-Volt Threshold
NFPA 70E and OSHA both treat 50 volts as the line where shock protection becomes mandatory. Section 110.2(B) of NFPA 70E directs employers to place conductors operating at 50 volts or more into an electrically safe work condition before work begins, unless de-energizing is infeasible or introduces greater hazards. OSHA mirrors this in 1910.333(a)(1), which requires live parts above 50 volts to be de-energized before an employee works on or near them, with narrow exceptions.
Why 50 volts? Because that is roughly the point at which a person can experience severe injury or death. Below it, exposure is generally considered lower risk, though wet skin, large contact area, and current path can change that calculation. The takeaway is to respect every voltage level, whether it is a 120-volt branch circuit or a 138-kV transformer.
Current Thresholds and the Human Body
The physiological data behind shock hazard analysis is sobering. A person can perceive AC current as low as about 1 milliamp. At roughly 10 milliamps of 60-Hz AC, muscle contractions become so strong that the victim cannot let go of the energized object — the well-known “let-go threshold.” A sustained 120-volt, 60-Hz shock is especially dangerous precisely because it usually exceeds the let-go threshold while lacking the energy to throw the person clear of the source.
Higher still is the ventricular fibrillation threshold, the point at which the heart’s rhythm is disrupted and circulation can stop. Ventricular fibrillation becomes increasingly likely as current magnitude and exposure duration increase.
Research summarized in IEC 60479 demonstrates that currents in the tens of milliamperes can become life-threatening when exposure is sustained. Above about 70 mA, tissue burning begins as electrical energy converts to heat. These thresholds explain why proximity, not just contact, is controlled through approach boundaries.
How a Shock Hazard Analysis Works (Step by Step)
A shock hazard analysis follows a repeatable sequence. While the exact wording lives in NFPA 70E 130.4, the practical workflow looks like this:
- Justify the work. Confirm whether energized work is even necessary. If the equipment can be de-energized, hazard elimination is the first and highest priority in the hierarchy of risk controls.
- Identify exposed energized parts. Determine whether any conductor or circuit part will be energized at 50 volts or more during the task. Boundaries do not exist without exposed energized parts.
- Determine system voltage. Establish the nominal voltage, since it sets the approach distances.
- Look up approach boundaries. Use NFPA 70E Table 130.4 for AC systems or the corresponding DC table to find the limited and restricted approach distances for that voltage.
- Select protective measures. Apply the hierarchy of risk controls — elimination, substitution, engineering controls, awareness, administrative controls, and PPE as the last line of defense. Choose insulated tools, barriers, and shock PPE such as insulating gloves rated for the voltage.
- Document everything. Record the assessment, the justification for energized work, the boundaries, and the PPE selected.
This shock hazard analysis must be completed for every task where energized parts may be present, and it should be revisited whenever conditions or scope change.
Shock Protection Boundaries Explained
The output of a shock hazard analysis is a set of approach boundaries — invisible lines around energized parts that define who may approach, how close, and with what protection. NFPA 70E defines two shock protection boundaries, drawn from Tables 130.4 for AC and DC system voltages.
Limited Approach Boundary
The limited approach boundary (LAB) is the outermost line and marks the distance at which a shock hazard exists. Unqualified persons must not cross it unless they are escorted and continuously accompanied by a qualified person. The tables list two values: a larger distance for movable conductors, such as a dangling wire, and a shorter one for fixed circuit parts like a bus bar. The larger movable-conductor figure accounts for a loose conductor swinging toward a worker.
Restricted Approach Boundary
The restricted approach boundary (RAB) sits closer to the energized part. Only qualified persons may cross it, and only with appropriate shock protection or insulation rated for the voltage. Failure to recognize that the shock hazard actually begins at the LAB — not the RAB — has exposed many workers to danger and caused confusion about when an energized electrical work permit is needed. The limited and restricted approach boundaries are based on electrical insulation characteristics and the probability of inadvertent movement resulting in contact. They are not arbitrary distances but are derived from decades of electrical safety research and industry experience.
Shock Hazard Analysis vs. Arc Flash Hazard Analysis
These two analyses are frequently conflated, but they protect against different things. A shock hazard analysis addresses current passing through the body from direct contact and produces the limited and restricted approach boundaries based on voltage. An arc flash hazard analysis addresses the radiant thermal energy of an electrical explosion and produces the arc flash boundary, defined as the distance at which incident energy reaches 1.2 cal/cm².
The boundaries are independent. In some cases the arc flash boundary extends farther than the limited approach boundary; in others the reverse is true. Arc flash temperatures can exceed 10,000°F at the source, vaporizing metal and propelling molten material. Because both hazards can exist on the same energized equipment, a complete electrical safety evaluation typically performs both a shock hazard analysis and an arc flash hazard analysis, then selects PPE and work practices that satisfy whichever is more demanding.
Documentation and OSHA Compliance
NFPA 70E was developed at OSHA’s request and is the consensus standard OSHA inspectors reference when investigating electrical incidents. Although NFPA 70E itself is not federal law, OSHA enforces equivalent outcomes through 1910 Subpart S, and it routinely cites failures in risk assessment as violations.
Documentation is where many programs fall short. The principle commonly repeated in safety training is blunt: OSHA cares about what you documented, not what you say you did. A defensible shock hazard analysis records the justification for energized work, the boundaries determined, the PPE selected, and the job briefing — and it is reviewed at least annually or whenever conditions change. When work occurs within the restricted approach boundary or under permitted energized conditions, an energized electrical work permit (EEWP) is generally required.
Frequently Asked Questions
When is a shock hazard analysis required? Whenever workers approach exposed energized conductors or circuit parts operating at 50 volts or more, and for every task with potential electrical risk under the 2024 edition of NFPA 70E.
What voltage triggers shock protection requirements? 50 volts. Both NFPA 70E and OSHA treat 50 volts as the threshold at which conductors must be de-energized or shock protection applied.
Who can cross the approach boundaries? Unqualified persons may not cross the limited approach boundary unless escorted by a qualified person. Only qualified persons may cross the restricted approach boundary, and only with appropriate insulation or shock PPE. Being a qualified person depends on documented training and demonstrated skill.
Is a shock hazard analysis the same as an arc flash analysis? No. A shock hazard analysis evaluates contact and current based on voltage; an arc flash analysis evaluates thermal energy. Both may be required for the same task.
Key Takeaways
A shock hazard analysis is the NFPA 70E-required evaluation that identifies shock risk, sets the limited and restricted approach boundaries from system voltage, and drives the selection of shock PPE and safe work practices. It hinges on the 50-volt threshold and on current thresholds — perception near 1 mA, let-go near 10 mA, fibrillation in the tens of milliamps. Paired with an arc flash hazard analysis and backed by thorough documentation, it is one of the most effective controls available for keeping electrical workers alive. The first and best control, however, remains the simplest: whenever possible, turn it off.
