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All about electrical risk assessments

What is the difference between an electrical risk assessment, a shock assessment and an arc flash assessment?

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Responding is Derek Vigstol, senior electrical safety consultant, e-Hazard, Quincy, MA.

An electrical risk assessment is made up of a shock risk assessment and an arc flash risk assessment.

First, how is risk defined? NFPA 70E 2021, the National Fire Protection Association’s standard for electrical safety in the workplace, approaches risk as the combination of likelihood of occurrence and the severity of injury or damage to health resulting from a hazard. With electricity, there are two primary hazards: shock and arc flash. Each hazard requires an independent assessment of every situation and task. The risk assessments are meant to answer the following questions:

  • Is a hazard present?
  • Is an injury likely to occur?
  • What’s the severity of the potential injury?
  • How is the risk mitigated in accordance with the hierarchy of risk controls?

Shock hazard: A shock hazard is defined as a source of possible injury from contact with/approach to exposed and energized electrical conductors or circuit parts. 70E also defines the limited approach boundary as the distance from exposed and energized parts where a shock hazard exists. Work through the following questions: A) Are exposed and energized parts (above 50 volts) present and will we cross the limited approach boundary? If so, there’s a hazard. B) Is an injury likely to occur? The restricted approach boundary is where an increased likelihood of injury exists. If this distance will be crossed, injury is likely. Severity is based on the voltage. Voltages above 50 may result in fatal or disabling injuries. Generally, the higher the voltage, the higher the severity, but many fatalities have resulted from 120 volts (single phase).

Lastly, determine an appropriate mitigation strategy per the hierarchy of risk controls. Consider this as a simplified approach for illustrative purposes only: Can we create an electrically safe work condition following our control of hazardous energy procedure (or lockout/tagout procedure)? If not, can we stay away? If not, can we substitute a different voltage? If not, can we put something between us and the hazard? And if none of those holds true, we might need to resort to personal protective equipment.

Arc flash hazard: The likelihood of occurrence is based on the interaction between employee and energized equipment, and 70E Table 130.5(C) helps with this determination. The likelihood of injury centers on being inside the arc flash boundary when a hazard exists, and severity is determined either by performing incident energy analysis or using the PPE category tables in 70E. However, the final piece remains: Can I create an electrically safe work condition? Can I stay away? Can I substitute? Can I put something between me and it? If not, PPE can be used to reduce the severity of injury to survivable levels.

Performing both risk assessments are critical to employee safety from electrical hazards. Keep in mind that both must also consider equipment design and condition of maintenance, as these factors can greatly affect results. However, once we understand the nature of the danger we’re exposed to, we can take effective steps to mitigate the risk and work safely.

Editor's note: This article represents the independent views of the author and should not be construed as a National Safety Council endorsement.

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