Arc Flash Calculations

Last updated: March 29, 2024

What Does Arc Flash Calculations Mean?

Arc flash calculations refer to the set of calculations used to determine the level of electrical hazard produced by a specific piece of energized machinery or other energized system. Specifically, these calculations determine the potential strength of an arc flash (incident energy) that workers would be exposed to at a given distance from an electrical hazard.

Arc flash calculations are mandatory in any workplace in which a person operates within the vicinity of an exposed and energized electrical source that has the potential to hold and discharge a hazardous level of energy.

Safeopedia Explains Arc Flash Calculations

There is no single method for performing arc flash calculations. For instance, the National Fire Protection Association’s NFPA 70E standard and the IEEE’s 1584 standard (a nine-step process) both use different methods of calculating arc flash strength.

NFPA Arc Flash Table

NFPA 70E provides a table-based system for use in workplaces that acts as a substitute for arc flash calculations. This system may be used for calculating hazards associated with electrical equipment whose properties meet the range of criteria that the tables have been designed to accommodate. The results of the calculation are used to determine the protective measures that must be put in place to protect workers and other persons who work on or in the vicinity of the energized equipment.

OSHA Arc Flash Calculations

OSHA’s general industry requirements for compliance with electrical safety are laid out in OSHA standard 29 CFR 1910.269.

In general, OSHA recognizes the NFPA’s 70E as a consensus standard and views compliance with 70E as sufficient for employers to meet their duty to provide safety. However, the calculations that OSHA allows vary depending on the level of voltage, number of electrical phases, and potential containment of the system that is producing the energy.

OSHA defines which calculations are acceptable for a given type of system in Appendix E of Standard 1910.269, and it requires that personal protective equipment (PPE) be worn by all workers who the calculations have determined are at risk of being exposed to an arc flash with a strength of at least 2.0 cal/cm2.

Arc Flash Boundaries

Arc flash calculations are primarily used to prescribe certain mandatory minimum distances from equipment that persons must remain in order to be safe from receiving a hazardous arc flash. These distances are demarcated by approach boundaries that require certain levels of PPE and electrical professional qualifications in order to work within them.

NFPA 70E requires specific PPE be worn and safe distances from electrical hazards be observed by workers, with the exact requirements varying depending on the result of the arc flash risk calculations.

Ready to learn more? Check out our free webinar on How to Build an Arc Flash PPE Program Your Workers Will Embrace!

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