Helinut
Totally agree - oxygen does indeed support combustion. I was just saying it wasn't the cause: ie there must have been another source of fire, but the oxygen may then have acted as an accelerator
SASless
Can't comment without more information. Correct checking of a medical oxygen system does NOT involve release of more than about 4 litres of gas at no more than 1.5 atmospheres. Unless you squirt this at an open flame it won't cause a problem.
Changing old style cylinders does require releasing at high pressure. This should be done away from the airframe before fitting the cylinder. Modern cylinders do not require venting or any release of oxygen
As with helicopters, failure to follow correct procedures with oxygen cylinders can be dangerous