I doubt oxygen would create a flame like that. Flamethrowers use a type of flammable gas or liquid. Oxygen can fuel a fire but not propel it in such a way as don't forget the atmosphere also contains oxygen.
It's the propellant used to create the pressure inside the tank. Depending on the chemicals used, and whats inside it, the contents could also be flammable. The Oxygen inside the ventilator would sure as hell help too