An arcing fault, which is the cause of an arc flash is described below.

Arcing faults (an Arc Flash) are defined as high-impedance faults, since any fault current must travel through air, as opposed to the low-impedance path normally associated with a short circuit. A short circuit study of the electrical system is required to determine the maximum available short circuit energy, which in turn may then be used to calculate the potential incident energy available.

There are intense heat and pressure waves associated with these types of faults.  This heat and pressure wave will cause shrapnel and molten metal to explode from the point of the fault.

The core temperature of an arc fault can easily reach 5000ºC (source), for comparison the surface temperature of the Sun is only 6000 ºC and the boiling point (not melting point, but BOILING) of copper is 2500ºC.

Assuming that the electrical protective device in the circuit operates fast enough to extinguish the fault so that these extreme temperatures do not cause greater than second degree burns to the operator, the ignition temperature of the typical non-PPE clothing the operator is wearing would have been reached, this burning will cause serious harm to the operator if they are not extinguished quickly

When proper PPE is worn for the calculated incident energy at the fault, the worker should walk away from the incident with a maximum of second degree burns.