The Role of Oxygen in a Shipwreck

Even the simple process of a shipwreck rusting consumes the oxygen within an environment making it anaerobic or non-oxygen. Another rule taught to every scuba diver is never take your regulator out in an airspace inside a shipwreck or cave. So Prabhuput would have needed to have been exploring a wreck sunk recently enough that it still contained oxygen, but not already contaminated by some sort of noxious gas or poison. But we already knew that. His next problem was that he's brought his own poison with him.