During my recent VIP class at DEMA they discussed this case. The diver had filled the tank with a nitrox mix, the tank had the burst valve removed and replaced with a plug and the neck at the valve appeared to be on fire at the time of the explosion. This would have denoted the use of a petroleum product of some time not suited for nitrox and the fill with a nitrox mix under high pressure caused the neck to leak fire and explosion followed. That is what I understood the offical report to have said according to the guys teaching hte class.