Oxygen does not explode, it is an ignitor. It will heat any carbon fast enough and then feed any resulting spark or flame to make for what we see as ,"an explosion." It is violent and then continues to feed flames.Doh! Seems my chemistry professor was a crack pot! Or maybe I just misremembered? Probably the latter. Either way, in a highly oxygenized (is that a word) environment, fires get bigger faster.
My commercial guy had to make a csa from 22 meters adn immediately went, cranked open our O2, instead of gently gently, and it took just a second to burn a hole in a gear bag against the valve and we lauched the tank over the side before it could truly dump out more O2. It goes up very quickly.
There is also the possibility that the valve rotated on impact and the friction in the threads caused ignition of metal dust and/or lubricant. There is one reported and investigated case where someone tried to tighten the valve of a filled O2 cylinder with explosive results.
OSHA requires compressed gas cylinders to be secured for a reason. Even without an explosion, a full cylinder with a broken-off valve becomes a missile that fully penetrates a cinder block wall - as shown in mythbusters.
Have you ever tipped a tank and the valve crack open a twist against the ground or whatever it falls against? Air flows. O2 tanks doing that can cause exactly what seems to have happened here. There doesn't have to have the valve break, just open a bit.
Yup. All of mine are standing up. But not my O2 tanks. We have our big blending tanks chained to the walls and then our emergency boat tanks are laid down in a crated in corner. We have seen a bottle open too quickly. We learned this already. I am very sorry this had to happen to them, but they don't have to have a "fault" for this. It was a terrible accident. I don't find blame, myself, here. Nothing more. An accident....OW students are taught to not stand their unattended tanks up because if they fall over the tank could crack the tile on the pool which means the LDS would have to pay for the repair. Plus it is supposed to get the student in the boat dive mindset where a standing, loose tank is never a good thing.
I have yet to see an LDS that stores their tanks other than standing and loose. It is a standard practice because tanks are not eggs.