The heat energy of an electric arc is measured in calories per centimeter squared (cal/cm²) in America and joules per centimeter squared (j/cm²) in Europe.
There are two important figures to remember.
The first is 1.2 cal/cm² or 5 j/cm². If bare skin is subjected to heat energy of this value for longer than 0.1 seconds then a second degree burn would be suffered. 1 cal/cm² is equivalent to holding your finger over the top of the flame from a cigarette lighter for 1 second.
The second is 40 cal/cm² or 180 j/cm². At heat energies of this rating, the other hazards, mostly the pressure wave, from an arc go beyond what a human can withstand and so death is highly likely to occur.
There are 3 main contributors that affect the amount of heat energy from an arc;
The gap between the electrodes
The time the current flows for
- The fault current flowing