Still it's kinda weird. Everyone knows the oxygen will not start to flow before the canister is activated by pulling the cord. So I guess they're worried also about the leftover oxygen people exhale actually? The problem is that fire burns in conditions where people already suffocate so it's a no win situation.
My experience is limited to working with commercial divers in hyperbaric chambers constantly using O2 to help rid the body of nitrogen to prevent the bends. In that environment, the chamber is so saturated with O2, a fire can be started with static electricity. That being said, this is just an educated guess: If the cabin of an airplane is filling with smoke and the O2 mask drops in front of you, you're going to put it on. O2 is going to flow and without proper ventilation, O2 will build up in the cabin and... boom. And yes, a fire in a pressurized, O2 saturated environment is a no win situation. The people inside are going to die. If you're outside, run. I cant find a link but there was a chamber in Italy that had a fire, it exploded, wiped out almost an entire hospital and they found the chamber door over a mile away.
