Arc Flash Accidents
Aside from electrocution and shock incidents, there is another major category of electrical accidents which does not necessarily involve contact with energized electrical parts. Instead, electricity travelling through unintended paths causes a rapid release of damaging energy. The temperature in an arc blast can exceed the temperature on the surface of the sun. People in the path of this energy are injured by the percussive force of the pressure wave, intense heat, radiation, and loud sound. This type of accident gained a great deal of attention in the industry after Ralph Lee, PE published his pivotal 1981 paper, “The Other Electrical Hazard: Arc Blast Burns”.
At the same time, statistics were showing that many more electrical injuries and deaths were occurring than could be explained by reported shock incidents alone. Eventually in 1995 NFPA 70E, “Standard for Electrical Safety in the Workplace” began increasingly devoting procedure to the prevention of arc flash incidents.
Today in the United States OSHA places specific burdens upon employers, contractors and engineers to protect workers from arc flash incidents. Some required actions involve identifying and assessing the need for an appropriate level protective gear, establishment of hazard boundaries at calculated distances, employee training and qualification, and equipment labels warning of the specific arc flash energy that could be encountered.
Arc flash theory is much more complex than shock theory, with as many unintuitive facts. For example, many licensed electricians do not realize that it is possible for the ubiquitous 208-volt panel to pose a higher arc flash risk than a 480-volt panel. The OSHA mandated assessments to determine arc flash energy requirements can be manually performed by licensed engineers on a spot basis, but as a practical matter a facility-wide study is typically performed by the PE’s using advanced software packages.
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