Biggest Threat to Submersible’s Passengers May Now Be Dwindling Oxygen

As search and rescue teams scour the North Atlantic for the missing submersible Titan, one overriding question may dictate the fate of the five passengers: How much oxygen is left?

The submersible contains a finite amount of oxygen, with no way of generating more. Once it is consumed, passengers would be left without breathable air. The craft is estimated to have started out on Sunday with about a 96-hour supply of breathable air; on Wednesday morning, the U.S. Coast Guard admiral in charge of the search said in a broadcast interview that the amount left had probably dwindled to around 20 hours.

There is no way to say any more precisely how much may be left.

Assuming the vessel is still intact underwater, several variables could help extend the survival time for the five people aboard, according to Dr. David Cornfield, a pulmonologist at Stanford University.

If they can remain calm and breathe less deeply and frequently, they might eke out several more hours. “They can very modestly change the curve,” Dr. Cornfield said. For instance, if they could slow their breathing enough to gain 10 percent more time, that would add nine hours of survival to the possible window for rescue.

The level of carbon dioxide, an invisible gas that is exhaled when breathing, also affects survival time. If carbon dioxide builds up too high, the people on board may grow sleepy, fall unconscious and eventually die. The Titan is said to be equipped with a scrubber, or filter, that is meant to extract excess carbon dioxide from air in the enclosed craft.

The submersible is a tight fit for a pilot and four crew members: 22 feet long, 9.2 feet wide and 8.3 feet high. Its small size is intended to allow undersea expeditions at relatively low cost, but experts have warned of structural risks and other concerns about the craft’s reliability. David Pogue, a CBS reporter and former New York Times technology columnist who has been aboard the Titan, described the interior as “about the size of a minivan.”

Images from OceanGate Expeditions, the company that operates Titan, show an interior resembling a metal tube. Passengers sit against the curved walls; there are no chairs for them, and little room to stand or move around.