They use these candles to help replenish the oxygen in them: https://www.youtube.com/watch?v=g3Ud6mHdhlQ
They use these candles to help replenish the oxygen in them: https://www.youtube.com/watch?v=g3Ud6mHdhlQ
Burning candles is a hassle and creates a big mess, to the consternation of junior enlisted who have to haul clinkers around and clean up the constant dust storm they leave behind. That said, huffing that good O2 straight out the spout will keep you awake, especially if your boat has been below 18% for awhile.
3k-lbs of pure O2 combined with a reputation for fires, rapid depressurizations, and hydraulic leaks. More than one auxiliaryman got blasted to bits by those things back in the '60s. Every submariner thinks theirs is a unique and special hell, but I don't envy those who went underway with the old O2 plants.
In Kursk it is suspected that it got dropped into water that had a lot of oil floating on top.
Also... even these show how difficult life on a submarine is (and the ultra-wide angle used most of the time shows how extremely claustrophobic everything is). Not exactly appealing. It takes some very special people to do this kind of job, and I doubt a lot of people are cut out for it...