If the passengers on the missing submersible died of oxygen deprivation, their final moments were likely mostly without pain, medical experts said, as the point at which the vessel’s oxygen was expected to run out passed Thursday.
If oxygen levels on the Titan fell, the travelers would notice effects on their brain, including impaired judgment and muscle coordination problems, said Juan Rojas, a pulmonologist at Rush University System for Health. Eventually, they would lose consciousness and die without sensing it.
"While it's sort of morbid and sad to say, the lack of oxygen in what they're dealing with is in some ways - I wouldn't say peaceful, but not as traumatic as some other end-of-life events," Rojas said.
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A similar scenario would play out if the adventurers died of elevated carbon dioxide levels, Rojas said. If the submersible's carbon dioxide scrubber lost power and became unable to absorb the gas, he said, that substance's buildup would also be terminal.
It's impossible to know exactly when the Titan's five travelers, who disappeared Sunday while descending to see the wreckage of the Titanic, would have lost the ability to breathe. The Coast Guard said Thursday that the submersible suffered a catastrophic loss of pressure that imploded the vessel, killing all five passengers.
The estimate from the U.S. Coast Guard and OceanGate, the company that owned and operated the submersible, that the submersible had a 96-hour oxygen supply is merely "a useful metric for everybody" and not a reliable number, submarine search and rescue expert Frank Owen told the Associated Press.
"It's based on a nominal amount of consumption the average human might consume in doing certain things," he said.
When someone experiences oxygen deprivation and a corresponding increase in carbon dioxide, the body goes into fight-or-flight mode by breathing heavier and increasing its heart rate, said Glen Chun, clinical director of the Mount Sinai National Jewish Respiratory Institute. The person may then experience headaches, nausea, vomiting or abdominal pain as the vital organs struggle to function.
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Those symptoms would probably then lead to feelings of confusion and, ultimately, sedation, said Chun, who is also a professor at Mount Sinai's Icahn School of Medicine. The person could experience brain injury and death within a few minutes.
Humans are used to functioning in the Earth's atmosphere, which is roughly 21 percent oxygen. The amount on a submersible would typically be slightly lower, Rojas said. If that percentage dips too far, anyone in that environment could survive only a few hours.
"The biggest analogy that we have in modern-day parlance is people who are climbing mountains and develop complications secondary to their altitude sickness," Rojas said. "You have a few hours to get them to a safer area and get them oxygen before they die."
On the Titan, the passengers could have saved a bit of oxygen by staying still and minimizing movement - but that behavior would only help if a rescue was imminent.
"Those topics are sort of a Band-Aid on the problem," Rojas said.
If the passengers remained on the Titan as their oxygen supply ran out, they may have felt slightly buoyed by at least not being alone.
“I offer these next words cautiously, lest they be read as unfeeling,” William Haning, a physician and professor emeritus of psychiatry at the University of Hawaii told The Washington Post in an email. “But in considering the fear of entrapment, certainly generalizable to all people, comfort most commonly comes from the presence of other people.”
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