Frequently Asked Questions

Q: What happens in an arc flash or arc blast?

A: Arc flashes cause electrical equipment to explode, resulting in an arc-plasma fireball. Temperatures may exceed 35,000° F (the surface of the sun is 9000° F). These high temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. The arc blast will likely vaporize all solid copper conductors; solid copper expands to 67,000 times its original volume when it is vaporized. In addition, measurements taken on a test mannequin during a laboratory arc flash detected sound levels of 141.5 decibels at two (2) feet from the blast, and pressure levels of 2,160 pounds per square foot (psf) in the immediate vicinity of the arc blast.

Q: What is NFPA 70 E?

A: NFPA 70 E is intended to provide guidance with respect to electrical safe work practices.

Q: What is the difference between NFPA 70 (NEC®) and NFPA 70E?

A: The National Electrical Code® is generally considered an electrical installation document and protects employees under normal circumstances. NFPA 70E is intended to provide guidance with respect to electrical safe work practices

Q: What standards regulate electrical safety and arc flash hazards?

A: There are four main regulations that govern electrical safety and arc flash.

1. OSHA Standards 29-CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E. OSHA compliance is required by any plant building or facility.

2. The National Fire Protection Association (NFPA) Standard 70 - 2002 "The National Electrical Code" (NEC) contains requirements for warning labels.

3. NFPA 70E provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized.

4. The Institute of Electronics and Electrical Engineers (IEEE) 1584 - 2002 Guide to Performing Arc-Flash Hazard Calculations