The pilot and four passengers on board the Titan submersible likely died instantly in a catastrophic implosion amid the intense water pressure in the deep North Atlantic, experts say.
Maritime researchers called an implosion the worst possible outcome of all the scenarios envisioned during the desperate around-the-clock search to find the missing vessel.
The craft went missing on Sunday and probably imploded that same day, according to an “anomaly” detected by a US navy acoustics system, but the international search effort continued because authorities did not consider the information definitive.
The coast guard announced the deaths from a “catastrophic implosion” on Thursday.
Crews are still looking for evidence of what occurred near the Titanic shipwreck, some 3800 metres below the surface.
Experts had cautioned that under intense pressure at extreme depths, the Titan’s hull could implode, which would result in instant death for anyone aboard the vessel.
“I don’t think people can appreciate the amazing energy involved in the destructive process of an implosion,” Bob Ballard, a member of the team that found the Titanic wreck in 1985, told US ABC News.
“It just takes out and literally shreds everything.”
While OceanGate Expeditions, which owned and operated the craft, touted the Titan’s roomier cylinder-shaped cabin made of a carbon-fibre, industry experts said it was a departure from the sphere-shaped cabins made of titanium used by most submersibles.
A sphere is a “perfect shape” because water pressure is exerted equally on all areas, said Chris Roman, a professor at the University of Rhode Island’s Graduate School of Oceanography.
The 6.7-metre long, 10,432kg Titan’s larger internal volume – while still cramped with a maximum of five seated people – meant it was subjected to more external pressure.
The water pressure at 3800 metres below the surface at the site of the Titanic wreck is roughly 400 atmospheres or 6000 pounds per square inch (more than four million kilograms of force per square metre).
Arun Bansil, a Northeastern University physics professor, likened that “humongous” pressure to the force of “a whale biting on somebody”.
While the Titan had a composite hull with in-built sensors that could withstand high pressures near the sea floor, any defect could result in a “near-instantaneous implosion” in less than 40 milliseconds, said associate professor Eric Fusil, director of the Shipbuilding Hub at the University of Adelaide in Australia.
“The passengers probably would have had no idea what happened,” Bansil said.
The Titan had made more than two dozen deep-sea dives, which put repeated stress on the hull, said Jasper Graham-Jones, an associate professor of mechanical and marine engineering at the University of Plymouth in the United Kingdom.
That stress could potentially cause delamination, a horizontal splitting of the carbon-fibre hull, he said.
Neither the coast guard nor OceanGate Expeditions have provided details on the implosion.
A similar disaster occurred in 1963 when the USS Thresher, a nuclear-powered submarine, likely imploded when it exceeded “test depth” after a series of other failures, killing 129 sailors and civilians on a routine test dive off Cape Cod.