[slowmovintarget]

Carbon dioxide levels will do them in before lack of oxygen.

[HWR_14]

Assuming they don't have filters onboard, yeah. I thought it was possible to filter out many man-days of CO2 with relatively small filters.

[slowmovintarget]

In a well-designed submersible that goes through thorough testing and gets a classification and rating... which I gather the CEO took short-cuts on. He's one of the passengers on board.