The Titan submersible, carrying five people to visit the wreck of the Titanic, tragically imploded thousands of feet below sea level.
The shocking event has left many asking why and how this happened after the US Coast Guard confirmed debris has been discovered by search crews hunting the Atlantic in a bid to locate the vessel. The hull is believed to have suffered a catastrophic implosion.
However, lots of questions remain unanswered, including simply 'how did this happen?' An official investigation into the circumstances is ongoing, but various marine experts have shared their insights and theories about the fatal accident.
Here are five theories posed by the experts as to why the tragedy occurred and what lead to the catastrophic implosion, reports the Mirror.
Failure of the hatch sealed by 17 bolts
Ryan Ramsey, a former Royal Navy submarine captain, shared his thoughts as he tried provide a possible reason for the implosion.
He stated that the implosion of the Titan submersible may have been caused when the hatch, which was secured by 17 bolts, failed. This may have then lead to the collapse of the hull under the huge pressure at that depth underwater.
He said: "The hatch with the 17 bolts they used to seal them in [might have] had a failure, which has then caused the hull to collapse at pressure because there is a huge amount of pressure, even halfway down."
The pressure hull had a defect
Another potential reason, according to Mr Ramsey, is the failure of the pressure hull itself.
The pressure hull may have had a pre-existing defect, which would cause the implosion if fractured under the immense pressure.
Mr Ramsey said: "The pressure hull itself [might have] had a defect in it when they sailed and that's fractured from the pressure and caused the same result."
However, he added that "the only positive out of it" is that the implosion occurred instantaneously, implying that those on the sub would not have been aware they were in impending danger if this situation was the cause.
Likely caused by "instability"
Manned Underwater Vehicles Committee chairman, William Kohen, said the implosion will likely have been caused by "instability".
The chief of the US-based company spoke on BBC Radio 4's Today Programme, explaining: "Clearly, something disturbed the pressure hull.
"If you've ever held a balloon and it just pops, if you just hold it lightly... something happened. An implosion is just a reverse explosion, so it exploded inwards."
Similar concernes were shared by Guillermo Sohnlein, a co-founder of OceanGate Expeditions, when he was asked about the cause.
"Anyone who operates in that depth of the ocean, whether it is human-rated submersibles or robotic submersibles, knows the risks of operating under such pressure and that at any given moment, on any mission, with any vessel, you run the risk of this kind of implosion", he said.
OceanGate refusing to submit to outside regulations
Previously, members of the Marine Technology Society's Manned Underwater Vehicles committee raised concerns over OceanGate's operations.
The committee voiced "unanimous concern" about the development of Titan in a letter and claimed it had not completed a standard risk assessment by Det Norske Veritas (DNV), an international maritime classification body.
The members emphasised that third-party validation was vital in order to ensure to safety of submersible occupants.
OpenGate, however, defended its decision to continue, stating that the goal was to pursue innovative design and operation outwith the established system.
The vessel was not subject to regulations by country as it operated in international waters. This meant that US laws did not need to be adhered to, including the rule that requires passenger submersibles to be registered with the coast guard.
Safety concerns were raised due to the lack of regulation, as questions increased about the accountability of OceanGate.
As the Titan was not solely a research vessel - designed also as a commercial vehicle to provide profitable expeditions to the Titanic wreckage - further concerns about the nature of the adventure industry surfaced.
The hull material was not suitable
Former Marine and deepwater salvage master, Robert Nester, explained he had declined a trip with Titan's predecessor at OpenGate, the Antipodes.
The expert is an experienced professional in the deep-sea industry, possessing great knowledge about the challenges underwater environments create, and explained that he deemed the equipment and materials used unsuitable for the depths aimed to reach.
He told the Daily Beast: "They were using off-the-shelf hardware from Radio Shack to operate inside, and quite frankly we’re talking about an environment that requires robust equipment that has certifications and qualifications that are established by different agencies for man-rated submersibles.
"None of the equipment that I saw inside the submersible was up to that [level], so I just chose not to go."
The ex-Marine believes that the implosion occurred due to the extreme conditions and the vessel's inability to cope with them.
Mester explained that a depth of 4,000-5,000 feet means the pressure is immense, amounting to around a ton-and-a-half per square inch.
He stated that even a small failure in the structure of the submersible or pressure chamber under such high pressure could leave to an implosion.
He went on: "Quite frankly, I found something else to take that time up, rather than take the trip.
"[The Titan] has a carbon fibre hull, which, how do I put this… it’s not a material that’s ever been successfully used at great depths.
"I believed from the start that the Titan had imploded. The pressure at that depth is a ton-and-a-half per square inch.
"It wouldn’t take much of a failure to cause an implosion, and it would have been instantaneous… a submersible can drop weight and come back to the surface, but nothing has gone beyond that one-and-three-quarter-hour timeline when they lost communication."
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