I can observe these breakers produce a small internal spark - I assume from the contacts separating. It seems reasonable that the same thing would happen (maybe greater) if a breaker trips under some type of fault condition.
Yes Mike, I've also seen this occur too.
I've reset breakers on to a fault before and witnessed things like a blue flame (as well as sparks) shoot out of them.
Now, this is assuming that the circuit breaker is properly matched to the PSCC of the service, I've seen under-rated breakers literally dis-integrate when asked to interrupt fault currents above their design rating.
Bear in mind, as PoCo wiring is upgraded, fault currents get higher because of larger conductors and transformers, people never seem to think that maybe the CB's in the panel might need an upgrade as well to cope with the extra PSCC.
{Edit:Look at them bare bits of busbar in the bottom of the panel, I would sort of think that these would be a real risk of explosion if someone dropped a metal tool amongst them, is there no requirement to shroud live terminals in a panel in the US, regardless of wether the cover is on it or not?)
