Arc flash is an important safety topic because many workers are injured or killed each year while working on energized equipment. Many of the electrical injuries that result in death are the result of exposure to an arc flash. The injuries that can result from an arc flash are burns, respiratory system damage, penetration of the skin by flying debris, hearing loss, and internal injuries caused by force from the blast pressure.
Electrical burns can be subdivided into three categories: arc burns, thermal burns, and conduction burns. An arc burn is caused by radiant energy. Thermal burns are caused by exposure to ejected hot gases and materials. Whereas conduction burns are caused by the transmission of electrical current through body parts. Burns from an arc flash damage the skin. The severity is based on the intensity of the heat generated by the electrical arc incident. The intensity of the heat that reaches the worker’s skin is dependent on the following three factors: first, the power and location of the arc; second, the distance of the worker to the arc; and finally, the duration of the exposure to the arc.
Burns are classified according to how deeply and severely they penetrate the skin. A first-degree burn is the least severe; the skin is red and sensitive to touch. With this burn, there is minimal skin damage, and only the skin surface is involved. A second-degree burn involves the first and second layers of skin. This type of burn causes the skin to blister and become extremely red and sore. Severe pain and swelling occur, and there is a risk of infection. A third-degree burn is the most severe; it causes charring of the skin and coagulation of the blood vessels just below the skin surface. All three layers of skin are affected.
Even at a distance of several feet, an arc flash can cause clothing to ignite. Clothed areas of a person’s body can be burned more severely than exposed skin. The intent of NFPA 70E regarding arc flash is to provide guidelines that will limit the onset of second-degree burns.
In addition to burns, an arc flash can cause respiratory system damage and injury from inhalation during the event. Some metals, such as copper, are vaporized at the high temperature produced by an arc flash. If the vaporized metal is inhaled, serious lung damage occurs when the vapor cools and solidifies in the respiratory system. When inhalation injuries are combined with external burns, the risk of death can increase significantly.
During an arc flash event, flying debris is also of great concern. Arcs spray droplets of molten metal at a high speed. Molten metal from an arc can be propelled for distances up to ten feet, and blast shrapnel can penetrate the body, causing devastating injuries.
The sudden expansion of an arc blast is very loud and can create a noise exposure up to 140 dB at a distance of two feet, which can cause permanent hearing damage.
Blast pressure waves created by arc flash explosions have thrown workers across rooms and knocked them off ladders. Pressure on the chest can be higher than 2,000 pounds per square feet. Not only can blast pressure directly cause damage to the body, but it can also create fall hazards.
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