Arc blast pressure

Electric arcs produce some of the highest temperatures known to occur on earth - up to 35000 degrees Fahrenheit, 19500 degree Celsius. This temperature is four times higher than the temperature on the surface of the Sun. The intense heat from an arc causes sudden expansion of air resulting in a blast. Copper expands during an arc flash event at a factor of 67000 times within a few milliseconds.

Because the chest and face area for most workers consists of nearly half square meter of surface area, the worker could easily be blown off his feets or somersaulted during intense arc flash explosion. As an example, 50 kA arc would provide enough pressure to propel a person standing 2 feet away from the arc source and weighting 75kg (170 lbs) with acceleration of approx 100 meters (330 feet) per second.

The arc flash blast energy or pressure is not currently addressed in IEEE 1584 or NFPA 70E. Ralph Lee's IEEE paper Pressures Developed by Arcs addresses arc blast phenomenon and provides the formula for calculating initial impulse force:

where,
P is pressure in lbs/ft²
Iarc is arcing current in kA
D is distance from arc in feet

Arcing current Iarc can be calculated using the online arc flash calculator, Arc-Flash-Analytic or the IEEE 1584 5.2 formula 2a and substituted in the above equation or simple arc blast calculator below:

Energies produced by arc flash explosions are comparable to dynamite explosions. These forces can be significant. They have been known to blow workers tens of meters away from the arc causing falls and injuries that may be more severe than the burns themselves.

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