What is 'catastrophic implosion,' the likely cause of Titan submersible destruction?

Despite a three-day-long rescue operation, the five men on board the 22-foot submersible that had gone to see the Titanic could not be saved.

It is believed that a "catastrophic implosion" may have destroyed the Titan submersible.

This conclusion was drawn by the US Coast Guard after examining debris found underwater Thursday through a remote-controlled vehicle. The debris was found 1,600 feet (488 metres) from the bow of the Titanic.

“We immediately notified the families,” Rear Admiral John Mauger said at a briefing in Boston on Thursday.

“On behalf of the US Coast Guard and the entire unified command, I offer my deepest condolences.”

The rescuers had to race against time as Titan’s 96-hour oxygen supply was dwindling after it lost contact with the Canadian research vessel Polar Prince on June 18.

International fleets of ships and aircraft were deployed to scour the North Atlantic in the hopes of finding survivors.

There were five men on board the Titan. They were Hamish Harding, 58, of the UK, founder of investment firm Action Group and an avid adventurer; French maritime expert Paul-Henry Nargeolet, 77; Stockton Rush, 61, chief executive officer of Everett, Washington-based OceanGate Inc., which ran the expedition; and Shahzada Dawood, 48, and Suleman Dawood, 19, a father and son in one of Pakistan's most prominent families.

What is catastrophic implosion?

A catastrophic implosion happens when a vessel collapses on itself due to overwhelming internal pressure. When the pressure within a confined space becomes too much for the structure to bear, it leads to a catastrophic collapse.

Titan's’ main body, or “the hull”, is made of carbon fibre and titanium. The carbon fibre reinforced plastic hull might have collapsed when the hull imploded.

“This is because the material is not ductile as metal alloys and therefore it catastrophically implodes,” Professor Stefano Brizzolara, the co-director of Virginia Tech Center for Marine Autonomy and Robotics, told ABC News.

At sea level, atmospheric pressure is 14.7 pounds per square inch (psi).

Water pressure at the depth where the ocean liner lies is equivalent to around 400 atmospheres, nearly 6,000 psi.

As a comparison, the bite of a large great white shark exerts a force of nearly 4,000 psi, according to Scientific American.

It is believed that the implosion might have caused a defect in the hull or for some other reason, causing the submersible to collapse on itself in milliseconds as it was unable to withstand immense water pressure.

The chances of survival become zero as the occupants would have died instantly.

According to reports, OceanGate Inc. of Everett, which built the Titan, had designed the vessel to sustain the extreme water pressure at a depth of 4,000 meters.

However, safety concerns were raised after a lawsuit was filed involving OceanGate's former director of marine operations, David Lochridge, who was fired in 2018 after warning about the Titan's "experimental" carbon fibre hull.

How the implosion might have happened

Experts noted that a flood or failure of the vessel to withstand water pressure might have likely caused the implosion.

“That kind of catastrophic event would have happened within 20 milliseconds," submarine expert Eric Fusil from the University of Adelaide told ABC News.

The pressure hull of the Titan was made of a combination of titanium and a composite material of carbon fibres. The navy submarines, on the other hand, use high strength steel or titanium alloys.

"The titanium pressure vessel is very elastic— it can crush and then restore its initial shape," Fusil was quoted as saying.

"But the carbon fibres are completely different — it's something very stiff."

He, however, argued that the use of carbon fire is an “experimental technology” and it was too early to tell whether that design caused the issues. 

What does an implosion feel like?

Fusil said that the five passengers on board Titan submersible might not have realised it was even happening.

"They wouldn't have realised they were dying because they cannot process that information that quickly," he was quoted as saying.

Forensic engineer Bart Kemper described the implosion to pricking a balloon. 

"When I take a needle and poke it into a balloon, once you break that balloon, it's gone," he said.

"That's exactly the problem you have with a pressure vessel, and the fact that this is external pressure, not internal pressure, it doesn't matter.

"Once you lose integrity, with these kinds of pressures, it's gone," he said.

Titan, the submersible that went down

The 6.7-metre-long Titan was designed to carry a pilot and four crew to a maximum depth of 4,000 metres (13,120 feet).

According to OceanGate's website, an onboard system was able to track the health of the crew and provide “early warning detection for the pilot with enough time to arrest the descent and safely return to surface.”

But no messages were received after a mothership on the surface lost all communications with the Titan on June 18, about 1 hour and 45 minutes after it began diving toward the Titanic, which sank in 1912 on its first trans-Atlantic voyage.