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Coex Training

Arc Flash/Arc Blast & Their Causes

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).

Examples include:

  • inadvertent shorting of conductors (i.e. dropped tools, covers);
  • loose connections;
  • insulation failure;
  • poorly maintained equipment;
  • inappropriate work practices;
  • vermin;
  • 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).

 

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