Search for missing Titanic submersible reaches critical point with oxygen due to run out within hours

Over the past few days, the world has been watching and hoping that the missing passengers of the Titanic submersible will be found.

However, as the hours trickle by, there is still no sign of OceanGate's small vessel, which disappeared on Sunday (18 June).

On board are: British billionaire Hamish Harding; Pakistani businessman Shahzada Dawood and his son Suleman; French explorer Paul-Henry Nargeolet; and OceanGate CEO Stockton Rush.

The vast search and rescue mission appeared to be making some progress yesterday (21 June), with noises heard coming from beneath the surface of the Atlantic Ocean.

Despite the signals, though, the search continues, and fears grow as the oxygen on board Titan is set to run out in the next few hours.

In a desperate bid to track the sub down, the US Coast Guard has doubled the search area, with teams now scanning 14,000 square miles.

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Giving an update on the search yesterday, Captain Jamie Frederick said people ‘need to have hope’ as the vessel’s air supply begins to dwindle.

"There are a lot of factors you have to consider," he said. "After considering all those factors, sometimes you’re in a position where you have to make a tough decision. We’re not there yet.

"If we continue to search, potentially we could be at that point ... That’s a discussion we will have with the families long before I am going to discuss here publicly."

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This comes as the medical expert Dr Ken Ledez told the BBC that running out of oxygen isn't the only threat facing the people on board.

Dr Ledez is a specialist in hyperbaric medicine at Memorial University in St John's, Newfoundland.

He explained there's an issue with the vessel possibly losing electrical power, which could affect the level of oxygen circulating in the cabin.

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Ryan Ramsey, who is a former submarine captain in the Royal Navy, also explained that there could also be a build-up of carbon dioxide.

"That for me is the greatest problem of all of them," he said.

There is also the risk of hypothermia, as the temperature on the sea floor at that depth is around 0C - and if the submersible has no power, then it cannot generate heat.

Dr Ledez added: "If anybody can survive in it, you know, it's these individuals. It just depends on them having power and depends on them having light to be able to find things and make these controls, but absolutely, they could still be alive."