An arc flash/arc blast is a dangerous electrical plasma explosion created by a short circuit through air that causes electric current to flash over from one exposed conductor to another or to ground. An arc flash/arc blast is characterised by the following characteristics:
- temperatures exceeding 20,000º Celsius;
- superheated toxic gases;
- airborne molten metal, copper expands at 67,000 times;
- blinding IR and UV light;
- extreme noise up to 180 dB;
- blast pressures up to 9764 kg/m2; and
- flying electrical components/debris.
The magnitude of the arc flash/arc blast is closely related to the fault current at the location and the fault clearing time. An arc flash/arc blast is an uncontrolled chaotic event, as opposed to the controlled interruption of current within the switchgear such as an isolator, circuit breaker or contactor.
Causes of arc flash/arc blast
An arc flash/arc blast incident can be caused by any of the following events, but over 80% of arc flash/arc blast injuries are due to human error, and are likely to occur at a point of change when people are present (i.e. switching, isolation, working live or other maintenance activities).
- inadvertent shorting of conductors (i.e. dropped tools, covers);
- loose connections;
- insulation failure;
- poorly maintained equipment;
- inappropriate work practices;
- voltage transients;
- failed short circuit interruption; and/or
- combination of effects
A total of 78 major arc flash/arc blast incidents occurred in WA from 2000 to 2007, as a result of:
- Incorrect work practices (48 incidents)
- Contact with live parts (12 incidents)
- Failure to isolate (11 incidents)
- Defective or damaged wiring (9 incidents).