answer:For one thing, the air was highly compressed, because of the depth of the wreck. So his breathing would have been much “shallower” in terms of oxygen usage, than it would have been at sea level. Credit the builder of the tug he was on, which fine construction enabled a relatively large bubble of compressed air to remain in what was never intended to be “a pressure vessel”. I don’t know the depth of the wreck, but judging by the squeaky voices of the divers on the audio track, and the fact that a decompression stage was required for the divers and the survivor, it had to have been fairly deep. So that air that he was breathing was quite highly compressed.