Missing Titanic submersible: Did French explorer Paul-Henry Nargeolet eerily predict his own fate? (WATCH)

Even as the search for the missing Titanic submersible enters a decisive phase, an old video of French explorer Paul-Henry Nargeolet, who is aboard the OceanGate vessel 'Titan', predicting what could happen if people get stuck in the Atlantic Ocean depth has gone viral.

On Sunday morning, the US company OceanGate's Titan submarine began its descent to explore the Titanic wreckage, but shortly after, all communication with its mothership was lost. Along with his son Suleman, British millionaire Hamish Harding, OceanGate CEO Stockton Rush, and French adventurer Paul-Henry Nargeolet, one of Pakistan's wealthiest individuals, Shahzada Dawood, is on board the ship.

Also read: Missing Titanic submersible: Haunting animation shows it could be stuck twice as deep as Great Canyon (WATCH)

Based on earlier estimations, the US Coast Guard predicted that those aboard might run out of oxygen within the next few hours. Officials in charge of the rescue effort say they must stay "optimistic and hopeful" as ten additional ships and several distant submarines joined the search, more than doubling efforts. Camera-equipped remote-controlled vehicles (ROVs) are scanning the depths of the seafloor. However, the captain leading the search has also said: "We don't know where they are, to be frank with you."

Amid the intensified search operation, an old footage of former French Navy diver, Paul-Henry Nargeolet, giving insights on what could happen if the submersible on a Titanic wreckage expedition gets stuck in the ocean bed has gone viral. The 77-year-old explorer has spent more time at the Titanic wreck than any other explorer and was part of the first expedition to visit it in 1987.

"If you are stuck on the bottom, you can survive for a while. You can stay for about 4-5 days on the bottom, which will not help very much. If nobody can help you... those 5 days with oxygen, with food, with water, and everything like that... but we know very well that we will die before with the temperature," said Nargeolet in an old interview.

"The real problem in the depth is the temperature. Because of the water, temperature is around 33 degrees and if you're in the sub and nothing is running anymore, making some heat, it is very cold... even if we have some equipment after a while you die because of the cold, which is not a bad way to die because you fall asleep and you don't suffer," Nargeolet added.

"But the pilot has to be very careful because especially on a wreck... it is a dangerous environment. When you're on the bottom, doing geology or biology, I will say there is no danger... but when you are around a wreck it's dangerous," the French explorer added.

Also read: Missing Titanic submersible: When director James Cameron warned of dangers of visiting shipwreck

According to a renowned marine biologist and oceanographer, the episode should serve as a lesson for the sector. David Mearns, known as "the shipwreck hunter," has contributed to the resolution of numerous significant maritime mysteries.

"I certainly feel that now an investigation obviously should happen. This sort of thing we cannot allow to happen, and my industry needs to look in on itself and reflect on bringing passengers to such remote locations and such great depths because if things go wrong, there are very, very few options to make a recovery," Mearns told the BBC.

He says in hindsight, the fact the Titan was not safety certified is a "cause for concern". "Would I choose a vessel without a classification? It’s not even allowed. I think that answers that," he added.

Also read: Missing Titanic submersible: When OceanGate was warned of 'catastrophic' dangers with expedition

Dr. David Gallo, a deep-sea explorer, is optimistic despite his belief that rescuing people who are stuck in Titan would require a miracle. According to him, the sounds coming from underwater are "credible and repeatable," therefore teams should assume they are coming from the submersible and act immediately to find it.

"We have to, at this point, assume that that's the submarine and move quickly to that spot, locate it and get robots down there to verify that is where the submarine is. They've got to go fully ready as if that was the sub because to locate it and get it up to the surface - it takes hours." he told ITV's Good Morning Britain.

• Titanic
• Titan
• Atlantic Ocean
• OceanGate