It is not a dumb question. Depending on where you're embarking from, equipment like this may already be available - though not with a 15-minute supply, more li

It is not a dumb question. Depending on where you're embarking from, equipment like this may already be available - though not with a 15-minute supply, more like a minute, perhaps. When I've flown from Norway in latter years, our survival suits (worn throughout the flight) have been equipped with a rebreather device - you bite down on a mouthpiece connected to a plastic bag integrated in your suit, and as you exhale into the plastic bag, you can then draw the same air back in again - no CO2 scrubbing. The mouthpiece is equipped with a valve which lets you breathe normally while above water; you then close it as you are submerged and breathe into the bag until you've reached the surface again. The idea being that this will do for a minute or two - and in that minute, you're either out of the wreck or dead. (I've asked the simulator instructor how long we spend underwater - he shrugged and said 'On average, six to fifteen seconds' - so a minute is a long, long time.)