About arc flash and arc blast

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An arc flash releases hot gas and radiant energy up to four times the temperature of the sun.
 

What is the difference between arc flash and arc blast?

Up to 77% of all electrical injuries are caused by arc flash incidents. When an arc fault occurs, the result is a massive electrical explosion. The light and heat emitted by the explosion is known as the arc flash, and the pressure wave is known as the arc blast. An arc flash releases hot gases and concentrated radiant energy up to four times the temperature of the sun’s surface, which can melt metal and cause severe radiation burns, damage eyesight, and result in fatalities. Such high temperatures are also capable of explosively vaporizing metals such as copper. The presence of vaporized metal can then feed and sustain the plasma arc and exacerbate its power. An arc flash essentially lasts until the overcurrent protective devices open the circuit. A fast-acting fuse may open the circuit as quickly as several milliseconds. The accompanying pressure waves can damage hearing or brain function and send loose equipment, tools, machinery, and debris flying to cause further injuries. Even if an arc blast doesn’t injure a person, it will damage equipment and cause downtime.

Causes

One of the major causes of arc flash is voltage transients (spikes), resulting from switching reactive loads or lightning strikes. The transient may last only microseconds, but it may also carry thousands of amps of energy. When such spikes occur while measurements are being made, they can cause a plasma arc to form—inside the measurement tool, or in the air outside. Other major causes of arc flash are things as simple as touching a test probe to the wrong surface, worn connections, gaps in the insulation, improperly installed parts, or dust and corrosion that cause resistance heating.

Consequences

Arc faults are potentially fatal to any personnel in the vicinity. The intense heat of the arc flash can severely burn human skin and ignite the clothing of anyone within several feet of the incident. Treatment for arc flash burns can involve years of skin grafts. Without proper eye protection, projectiles and molten debris can cause eye damage. The intense UV radiation associated with the flash can cause retinal damage. Superheated vapors can injure lungs and impair breathing. The thermoacoustic blast can damage hearing with ruptured eardrums, cause collapsed lungs and damage other internal organs. The blast can knock personnel off their feet; falls may result in broken bones or lead to electrocution or further injuries on other parts of the system.

Arc flash and arc blast are real dangers in industrial electrical environments. By following best practices, using the proper equipment and staying as far away from energized components as possible you can reduce your risk of those events and work smarter and safer.

For more information on Electrical Safety, see our online course available at the Fluke eLearning Center.

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Arc Flash and Arc Blast

Crucial discussions of arc flash and arc blasts, including safety and prevention information.