Holy cow! Filling a tank and have a catastrophic failure? Any idea if it was a gun mounted one, or if it was a bulk tank? Even the small tanks can hold some serious energy if they let go before the burst disk.
That sort of thing was always my concern filling HPA tanks at the paintball field because all it would take is someone putting oil in a fill nipple trying to help out a worn O-ring to turn a 3k or 4.5k psi tank into shrapnel while you are holding it right next to your body during a fill.