When an electric current passes through air between ungrounded conductors or between ungrounded and grounded conductors, the temperatures can reach 35000F.
Exposure to these extreme temperatures both burns the skin and causes the ingnition of clothing. Each year more than 2000 people are admitted to burn centers with severe arc-flash burns.
An arc-flash can and do kill at distances 10ft or greater.
Source: NFPA 70E-2004, Annex K.3
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