5 aboard lost Titanic sub could survive for 'hours' after airtank depleted: Doctor

Despite their onboard oxygen tank expected to be depleted sometime Thursday morning, one doctor says they may have more time if the passengers are still alive. He estimates the five people aboard the lost Titanic tourist sub could survive for 10 to 20 hours with air still circulating through the experimental capsule.

Dr. Richard Moon, a professor of anesthesiology at Duke University, said that despite conditions being dire, those aboard the OceanGate Expedition's submersible could extend the oxygen available after its tank is depleted by staying calm and moving as little as possible.

"The actual amount of time that they have is unpredictable, but it's probably less than 24 hours after the final oxygen in the tank is depleted," Moon, director of the Duke Center for Hyperbaric Medicine and Environmental Physiology, told ABC News.

The Titan submersible had 96 hours of oxygen when it set off on its journey to the Titanic wreckage around 8 a.m. on Sunday, according to the U.S. Coast Guard. The sub pilot, OceanGate founder and CEO Stockton Rush, lost contact with its companion surface ship an hour and 45 minutes into the trip and hasn't been heard from since, setting off a desperate search off the coast of Newfoundland.

Coast Guard officials said the minivan-sized vessel's air tank is expected to be depleted sometime Thursday morning.

"When you have an enclosed vessel, such as the Titan, everybody is using oxygen, everybody is producing carbon dioxide, which is scrubbed from the environment by carbon dioxide absorbent materials," Moon said. "So, there would be an electric fan that would be blowing the air through a carbon dioxide absorber and I don't know what the lifespan of that would be. It would be at least as long as the oxygen will last, but it may be longer" assuming there were no mechanical failures compromising the fan.

He said that under normal circumstances, the average male uses about a third of a liter of oxygen per minute and the average female uses about a fifth to a quarter of a liter of oxygen per minute.

"Once the oxygen tank ... is depleted, then they will be left with whatever oxygen is in the environment at the time. As I understand the dimensions of the submarine craft, the internal volume is around 37,000 or 40,000 liters, of which a fifth would be oxygen," said Moon.

“So, multiply the daily minute-by-minute requirement of oxygen by five and you can calculate how long it would take until the oxygen level is depleted down to a level where they might lose consciousness or actually die," he said.

He said things would become "very uncomfortable" for the people aboard the vessel once the available oxygen level falls to between 6% and 10%.

"You can maintain life at 10%," said Moon, adding that survivability would also depend on whether the sub's occupants are all physically fit and have no underlying health issues. "But things are becoming very uncomfortable, people get short of breath, and down around 6%, I think would probably be the lowest level that might be tolerated. And if you do that calculation, you come to a number somewhere between 10 and 20 hours once the oxygen (tank) is depleted."

Moon, who is also a former director of the Divers Alert Network, a nonprofit dedicated to improving SCUBA diving safety, said there are steps that could be taken to extend the amount of oxygen.

"Staying calm and not moving would be about the only thing that can be done," Moon said. "It's possible to reduce the oxygen level further if there are any sedative drugs. So, taking Valium, for example, will reduce oxygen requirement a little bit. But in reality, I doubt there's any medication like that on board. They would just have to sit and not move to the extent that they can. Anything to avoid muscular activity would be helpful."

But he said once the oxygen level falls below 10%, those aboard the sub will feel the "alarming" effects of oxygen deprivation.

“But assuming the [carbon dioxide] scrubbers are still working, the amount of oxygen at 10% would cause shortness of breath. Everybody would be panting. They’d feel undoubtedly a headache. They may be vomiting," Moon said. "It’s like being at altitude and they would feel very uncomfortable. And then at some point, they would lose consciousness and where exactly that would be would vary by individual somewhere between 6% and 10% I would estimate. And then if the oxygen goes much lower than that it may be incompatible with life."

A report from the U.S. Department of Labor says that breathing 6-10% oxygen can result in becoming ill or unconscious, less than that level causes breathing to cease.

During a 2020 virtual field trip via Zoom with EarthEcho International, an environmental nonprofit organization, Stockton Rush said sub-pilots for his company are trained to stay calm in all situations.

"We try to think about anything that can go wrong. And we have procedures in place to properly handle those emergency situations, whether it's a fire or there's an air leak," OceanGate sub-copilot and project manager Mikayla Monroe said during the virtual field trip. "We have ways to stop these problems or get back to the surface as soon as we can."

Monroe added, "One of the very important things that we go through in sub-pilot training is how to handle emergency procedures. One of the main things that is consistent across emergencies regardless ... is to remain calm, especially as a pilot because everyone is looking at you for what's going on."

During the virtual field trip, Rush added, "There hasn't been a serious injury in a commercial sub, not a military one, in over 35 years and there have been millions of people who go in subs."

"So, it's scary, but it's very safe," he said.