It is a claustrophobic, terrifying prospect – being trapped in a 22ft submersible, potentially thousands of feet underwater, with oxygen running out.
The exact whereabouts of the Titanic submersible and the condition of the five crew onboard are unknown. It is thought that, if the vessel is still intact, it may have just a little amount of oxygen remaining, creating a race against time to find the sub before it is too late.
However, that timeline is not necessarily rigid. Dr Ken LeDez, a hyperbaric medicine expert at Memorial University in St John’s, Newfoundland, has told BBC News that, depending on conditions, some of those aboard could survive longer than expected.
“It depends on how cold they get and how effective they are at conserving oxygen,” he said, adding that shivering will use up a lot of oxygen, while wrapping up in a huddle can help to conserve heat.
He said running out of oxygen is a gradual process. “It’s not like switching off a light, it’s like climbing a mountain – as the temperature gets colder and metabolism falls [it depends] how fast you ascend that mountain,” he said.
While admitting that we do not know the full situation inside the submersible, Dr LeDez said conditions could be different person-to-person, and that although it is a “disturbing conversation”, some could survive longer than others.
On Wednesday, Rear Admiral John Mauger from the US Coast Guard said there were a number of unknowns in the search and rescue mission.
“We do not know the rate of consumption of oxygen per occupant on the sub,” Rear Adm Mauger told the BBC.
Dr LeDez also said that running out of oxygen is not the only danger those on board face.
The vessel may have lost electrical power, which is likely to have a role in controlling the amount of oxygen and carbon dioxide inside the vessel.
As the oxygen level falls, the proportion of carbon dioxide being breathed out by the crew will be rising, with potentially fatal consequences.
“As levels of carbon dioxide build up, then it becomes sedative, it becomes like an anaesthetic gas, and you will go to sleep.”
Too much of the gas in a person’s bloodstream, known as hypercapnia, can kill them if not treated.
Former Royal Navy submarine captain Ryan Ramsey says he looked at videos online of the inside of Titan and could not see a carbon dioxide removal system, known as scrubbers.