The missing submarine had enough oxygen to sustain those onboard for four days, but limited air is far from the only hazard

For an expedition as hazardous as the Titan’s descent to the Titanic, there is a long list of onboard systems that need to be checked and a host of environmental hazards that must be identified and assessed before the voyage begins.

“When you are putting people in a potentially dangerous position like this you want to be absolutely sure everything’s checked through before getting under way,” said Stefan Williams, a professor of marine robotics at the University of Sydney. “We have an extensive checklist before we put anything in the water.”