Why did the Titan submersible implode?

The four-day long search for the missing Titan submersible operated by OceanGate to take visitors down to the Titanic wreckage came to a tragic end on Thursday, 22 June, with the US Coast Guard announcing all five people on board — both pilot and passengers — are believed to be dead.

Debris found near the Titanic is believed to have come from the sub's implosion under deep-sea pressure — but why was it not able to withstand the environment it was ostensibly built for?

A remote-controlled vehicle (ROV) that was part of the underwater search team found a "debris field" on the ocean floor, approximately 488 m (1,600 feet) from the bow of the sunken Titanic.

The way the pieces of debris were located indicates "a catastrophic implosion of the vessel", said Coast Guard rear admiral John Mauger at a press conference in the US city of Boston.

How did the submersible implode?

While there can be no definitive proof of what happened, experts believe the implosion happened on Sunday, 18 June, itself — the first day of the dive.

The water pressure at 3,800 m below the surface, which is the depth of the Titanic wreckage, is roughly 400 atmospheres (6,000 PSI) — about the same as having 35 elephants on your shoulders.

The Titan's hull was made of carbon fibre and titanium, apparently designed to withstand water pressure at depths of up to 4,000 m.

However, experts have questioned the use of the combination of titanium and carbon fibre together for this deep-diving expedition, as the materials have somewhat contrary properties separately.

"Any deep divers know how unforgiving the abyssal plain is: going undersea is as, if not more, challenging than going into space from an engineering perspective," said Eric Fusil, director of the Shipbuilding Hub for Integrated Engineering, University of Adelaide, Australia.

Titanium is elastic and can adapt to a large range of stresses and pressures without permanent strain on the material. Carbon fibre on the other hand is stiffer and non-elastic, often prone to cracking.

Writing in The Conversation, Fusil speculated that these differences could have created a defect in the hull, triggering 'an instantaneous implosion due to the underwater pressure'.

Everyone within would have died in less than 20 milliseconds, a speed faster than the brain can even process information — thankfully, then, a likely painless death.

'Within less than one second, the vessel — being pushed down on by the weight of a 3,800 m column of water — would have immediately crumpled in from all sides,' Fusil wrote.

Exploring the ocean depths

Tourists do remain fascinated with exploring the deepest recesses of the ocean. In that sense, the Titan was far from unique. But is a deep-sea entertainment expedition always this risky? Was the Titan in unusually difficult waters?

Not necessarily.

In 2012, Canadian filmmaker James Cameron set off on a deep-sea expedition to the deepest point on Earth, into the Mariana Trench, aboard the submersible Deepsea Challenger (aka DCV 1). He collected data and footage at depths of around 10,900 m — over double the depth of the Titanic wreckage.

In fact, his trip into the Trench came exactly 100 years after the Titanic sank to the ocean floor. Cameron had also visited the Titanic wreck himself in earlier deep-sea voyages.

He wasn't the first or last into the Trench either.

In 2019, American explorer and private investor Victor Vescovo set a world record in the Mariana Trench, where he reached 10,928 m — 16 m deeper than the previous record set by Don Walsh and Jacques Piccard in 1960.

It was with one of those lost with the Titan, billionaire Hamish Harding, that Vescovo had also set a world record for the longest time spent in the deepest part of the ocean on a single dive — together, they spent 4 hours and 15 minutes traversing the Mariana Trench in 2021.

On board, the Titan is also the former French navy captain Paul-Henri Nargeolet, who has often dived to the Titanic wreck. A few years ago, in an interview with the Irish Examiner newspaper, he said, 'In deep water, you're dead before you can realise what's happening.'

The 77-year-old has been head of the research programme at the RMS Titanic/Phoenix International, which owns the salvage rights to the wreck, since 2007.