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.

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

I hope to discuss the topic with little if any "sales prejudice" since I am a consulting engineer for a medium sized General Engineering firm.  I will discuss different presentations that I have been to that were given by fuse manufacturers, breaker manufacturers and try to point out the prejudices that are evident in what they say, and why you have to take everything that people tell you as defintes regarding Arc Flash with a grain of salt.

There will be some articles that will be technical in nature, so if you are reading this and don't understand something please be sure to make a comment asking for clarification.  I will do my best to help you fulling understand the topics.