Arc Flash Hazards

What Is Arc Flash?

An arc flash is an electrical explosion where an electric arc is supplied with enough electrical energy to cause substantial damage, fire or injury. Arc flash temperatures can reach or exceed 35,000 F (20,000 C) at the arc terminals. A massive amount of energy is released, rapidly vaporizing the metal conductors, which blasts the molten metal and expanding plasma outward with extreme force. An arc flash explosion can cause destruction of equipment, fire, and injury to anyone in the area.

Arc flash and blast hazards were not formally studied until 1993 (IEEE 1584 began study). According to the "Practical Solution Guide to Arc Flash Hazards":

  • Electric arcs produce the highest temperatures on earth (up to 35,000 F -- 4 times the temperature of the sun)!
  • The intense heat from an arc flash causes the sudden expansion of air that results in a blast with very strong air pressure.
  • All known materials are vaporized at this temperature.
  • Arcs in enclosures magnify the blast and energy transmitted as the blast is forced to the open side of the enclosure.
  • Arcs spray droplets of molten metal at high-speed, creating shrapnel that can penetrate the body.
  • Blast pressure waves can throw workers across the room or knock them off ladders.
  • Clothing can be ignited several feet away, causing severe burns.
  • The sound of the blast can have a magnitude as high as 140 dB at a distance of 2 feet from the arc and cause hearing loss.

Arc Flash Label

How to protect against Arc Flash

According to Chapter 1, Section 130 of NFPA 70E-2004, you can protect against arc flash injury by having:

  1. Justification for live work
  2. Work permits secured (if applicable)
  3. Approach boundaries established

NFPA 70E compliance

NFPA 70E (Standard for Electrical Safety in the Workplace), provides guidance for 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.

To comply with NFPA 70E for flash protection:

  • Determine the Flash Protection Boundary
  • Determine the incident energy exposure level
  • Determine the Protective Clothing and PPE

Arc Flash protection boundary is an approach limit at a distance from exposed live parts within which a person could receive a second-degree burn if an electric arc flash were to occur (NFPA 70E).

Section 110.16 of the 2002 NEC® Requires Arc Flash Hazard Labels

110.16 Flash Protection. Switchboards, panelboards, industrial control panels, and motor control centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

FPN No. 1: NFPA 70E-2000, Electrical Safety Requirements for Employee Workplaces, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment.

FPN No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.


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