UPDATED BELOW. As I’m writing this, the oxygen level in the submersible Titan is dwindling, leaving its occupants with a just a few hours of O2. The crew of five men started out on Sunday with dreams of seeing the most famous shipwreck in the world: the HMS Titanic. Now they’re missing, left in a small vessel with just a few hours of breathable air remaining. In fact, they may be dead at the time this post publishes.