Arc Flash Protection and Prevention

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An arc flash is an explosion caused by arcing electricity. The explosion is caused by the huge amount of energy that can be used in industrial systems, which may operate at many megawatts of power. When such a system has a high fault current every second the arc is occurring there is a vast amount of energy being transferred to the surrounding environment. This causes a very rapid temperature rise of touched objects and the atmosphere and a high amount of potentially high energy EM radiation.

The primary damage caused by the arc flash is from the heat, which can reach up to 20,000 Kelvin, which is around 4 times the temperature of the surface of the sun. At these kinds of temperatures no known substances are known that wouldn't vaporize. While most arc flashes won't reach these extreme temperatures, temperatures will still be very high; due to this anybody close to an arc flash who gets hit by the arc will likely take sever damage.

The huge increase in temperature also causes rapid expansion of gasses as well as more gasses being created from vaporization of the surrounding materials. This is what causes the blast wave or arc blast which is associated with arc flashes. This shockwave is often the cause injury to people slightly removed from the actual arc because of the large amount of high velocity material that can be released, which can include molten metal and plasma as well as the force of the explosion itself and the noise levels which can cause permanent hearing damage.

As mentioned earlier, the arc flash can also release high energy radiation such as UV radiation which can blind or severely damage the eyesight of those unaffected by the actual blast (as well as those affected by the blast directly).

In the USA on average around 5 to 10 arc flashes causing serious injury will occur every day and around 2000 people a year are taken to burn centres each year from the effects of arc flash and blasts. Of these people, many were completely unaware of the possibility of an arc flash and most are unaware of the severity of the dangers involved.

There are many different methods of prevention and mitigation. The most obvious of course is powering down equipment before performing maintenance. Training staff properly of the dangers involved is very important too, since many accidents occur when staff are performing maintenance and drop tools into circuit breakers or attempt to take readings across high potential differences. To mitigate the effects of an arc flash, the fault current can be controlled with the use of fuses or grounding resistors. Arcing time may be reduced by lowering set points during maintenance, which will greatly reduce the released energy. One of the most effective methods is to use an arc eliminator, which will redirect the fault in milliseconds and greatly reduce arc time.