Understanding Arc Flash Hazards

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Understanding Arc Flash Hazards

Arc Flash is an electric current that passes through air when insulation or isolation between electrified conductors is no longer sufficient to withstand the applied voltage. The flash is immediate, but the result of these incidents can cause severe injury including burns. Arc flashes also can destroy equipment causing extensive downtime and requiring costly replacement and repair.

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The losses add up, as 5 to 10 arc flash accidents occur every day in the United States. More than 2,000 people are treated annually in burn centers with arc flash injuries and 1-2 deaths occur per day from an arc flash incident. Note that these are burn injuries, not electrical shocks. It is not necessary to touch live components to sustain an arc flash injury.

An arc flash may be caused by a tool, rodent or other element in a breaker or service area, that could compromise the distance between energized components.  Incidents often occur when personnel fails to ensure that the equipment has been properly de-energized.

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Arc Flash Physics

Electrical arcs produce some of the highest temperatures known to occur on earth, up to 35,000°F (19,426 °C). This is 4 times the temperature of the surface of the sun which is about 9000°F (4982°C). When materials vaporize, they greatly expand in volume, notably Copper-67,000 times (compare to water, 1670 times). This intense heat from the arc causes a blast with very high pressure.

An arc flash can cause injuries, depending on distance and exposure.  These can range from minor burns, escalating to third degree burns and potential death as well as other significant injuries including blindness, hearing loss, nerve damage and cardiac arrest.  Fatal burns can occur when the victim is several feet from the arc. Serious burns can occur at a distance of 10 feet. Staged tests have shown temperatures greater than 437°F (225°C) on the neck and hands of a person standing close to an arc blast.

Arcs spray droplets of molten metal at a high speed. Molten metal from an arc can be propelled for distances up to 10 feet. Blast shrapnel can penetrate the body. Blast pressure waves have thrown workers across rooms and knocked them off ladders. Pressure on the chest can be higher than 2000 lbs/sq. ft.  Clothing can be ignited several feet away. Clothed areas can be burned more severely than exposed skin.


Arc Flash Safety and Prevention

Arc flash analysis must be performed prior to allowing personnel to work on energized equipment. The analysis defines the flash protection boundary distance and the type of Personal Protection Equipment (PPE) required.

Four separate industry standards establish practices for the prevention of arc flash incidents in the United States:

  • OSHA 29 Code of Federal Regulations (CFR) Part 1910, Subpart S (addresses standards for work practices)
  • NFPA 70-2005, National Electric Code (contains requirements for warning labels)
  • NFPA 70E-2004, Standard for Electrical Safety Requirements for Employee Workplaces (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)
  • IEEE Standard 1584-2002, Guide for Performing Arc Flash Hazard Calculations

The Occupational Safety and Health Administration (OSHA) is an enforcer of safety practices in workplaces within the United States. OSHA 1910.132 (d) and 1926.28(a) states that the employer is responsible to assess the hazards in the work place, and to select, have and use correct PPE and document the assessment. The employer is required to conduct hazard assessment in accordance with 29CFR1910 132(d).

The NFPA 70E standard contains detailed information on how to protect workers from the heat of electric arc exposures. Preventative maintenance, worker training, and an effective safety program can significantly reduce arc flash exposure.

Flash Protection Boundary

The flash protection boundary is an imaginary sphere that surrounds the potential arc point “within which a person could receive a second degree burn if an electrical arc flash were to occur,” according to

NFPA 70E.

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Employers who conduct the hazard/risk assessment, and select and require their employees to use PPE, as stated in the NFPA 70E standard, are deemed in compliance with the Hazard Assessment and Equipment Selection OSHA Standard.