Arc flash is a serious industrial accident where electrical current leaves its intended pathway and travels through the air. Between five to ten arc flash explosions occur in the USA every day, with 2,000 people a year treated in burn centers for arc-related injuries.
Who’s at Risk of Arc Flash Injuries?
When an arc flash occurs, the energy created travels outward in a sphere with the origin point of the flash as the center. Anyone within the sphere is at risk of second-degree burns. Those outside the sphere may still be at risk from fires, shrapnel, or other complications of the blast.
While electrocution is an obvious risk of an arc flash, most arc-related injuries occur because of heat. An arc flash can produce temperatures of up to 35,000 degrees Fahrenheit—four times the temperature of the Sun’s surface. Even though the actual flash lasts only milliseconds, such heat is enough to ignite flammable clothing, damage eyes, and cause serious burns.
The incident heat produced by an arc flash is made up of convection heat and radiated, or infrared, heat. Fatal burns are possible within several feet of an arc flash, with second degree arc flash injuries possible up to ten feet away.
Properly worn PPE within a potential arc flash radius greatly reduces the risk of serious burns. Incident heat drops quickly the further away from the flash center a person is standing. Workers should perform their tasks as far away from energized equipment as is feasible, as even the space of a few inches can reduce the risk of serious arc flash injuries. For instance, the standard working distance from equipment operating at 600 kV is a mere eighteen inches, but even this short distance reduces exposure to incident heat. For higher voltages, the safe distance increases.
Blast Radius Injuries
Incident heat isn’t the only cause of arc flash injuries. When equipment arcs, the resulting temperatures are high enough to vaporize metal, producing a sound blast and pressure wave as solids transform instantly into liquid. The pressure wave can reach forces of thousands of pounds per square foot, more than capable of knocking employees off their feet or tumbling from elevated locations. Remember the blast expands as a sphere, so arc flash injuries are possible for employees working above the flash’s origin point.
Shrapnel from the blast is another concern. Those working further away from the flashpoint may be struck by molten or flying metal moving at speeds as high as 700 mph. In addition, the sound blast can produce over 160 decibels, causing ruptured eardrums.
All this happens in an instant. In the aftermath, employees may be at risk of fires caused by the original flash, which, depending on the production floor, can ignite flammable or volatile materials. Arc flash injuries are among the most serious accidents a company can face, making training and prevention extremely important.