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SESK: Stuff Everyone Should Know · sesk.info/elec-arc-flash-boundary

The arc flash boundary is the distance at which incident energy equals what?

The boundary is where incident energy is 1.2 cal/cm2.

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  1. 12 calories per square centimeter
  2. 40 calories per square centimeter
  3. 1.2 calories per square centimeter ✔

Why: 1.2 cal/cm2 is roughly the level that can cause a second-degree burn on bare skin. Inside that boundary you need arc-rated PPE.

Huh, didn't know that: The boundary distance can be calculated or taken from tables in NFPA 70E.

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References

Answer: 1.2 calories per square centimeter. 1.2 cal/cm2 is roughly the level that can cause a second-degree burn on bare skin. Inside that boundary you need arc-rated PPE.

  1. EC&M: 10 Questions Every Electrical Worker Should Know www.ecmweb.com/neca-show-coverage/article/55021477/10-questions-every-electrical-worker-should-know-how-to-answer
    the distance at which the incident energy equals 1.2 cal/cm2.
    Checked 2026-10-10.
  2. Cal Poly Electrical Safe Work Practices afd.calpoly.edu/ehs/docs/general-safety/electrical-safe-work-practices.pdf
    Anything 1.2 cal/cm2 or above requires an arc-rated face shield and clothing
    Checked 2026-10-10.

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