Despite repeated warnings over the safety of OceanGate’s Titan submersible, the CEO of the company dismissed them, according to e-mail exchanges with a leading deep-sea exploration expert.

Rob McCallum urged OceanGate CEO Stockton Rush to stop using the sub until it had been certified by an independent agency in messages seen by the BBC.

Mr Rush responded that he was “tired of industry players who try to use a safety argument to stop innovation”.

Mr McCallum said OceanGate’s lawyers threatened legal action after the tense exchange.

“I think you are potentially placing yourself and your clients in a dangerous dynamic,” he wrote to the OceanGate boss in March 2018. “In your race to Titanic you are mirroring that famous catch cry: ‘She is unsinkable'”.

Mr Rush, who was among five passengers killed in the Titan’s “catastrophic implosion” on Sunday, expresses frustration with Titan’s safety measures in the messages.

“We have heard the baseless cries of ‘you are going to kill someone’ way too often,” he wrote. “I take this as a serious personal insult.”

Canadian investigation

Canadian government regulators on Friday opened a safety investigation into the undersea implosion of a tourist submersible that killed all five people aboard during a voyage to the century-old wreck of the Titanic.

A debris field from the submersible Titan was found at the bottom of the North Atlantic on Thursday by a robotic diving vehicle deployed from a Canadian search vessel, ending an intense five-day international rescue effort.

Fragments of Titan, which lost contact with its surface support ship about one hour and 45 minutes into a two-hour descent on Sunday, were discovered on the seabed about 1,600 feet (488 meters) from the bow of the Titanic wreck, about 2-1/2 miles (4 km) below the surface, U.S. Coast Guard Rear Admiral John Mauger said.

He told reporters on Thursday the debris was consistent with “a catastrophic implosion of the vehicle,” meaning the 22-foot-long vessel ultimately collapsed and was crushed under the immense hydrostatic pressure at that depth.

International effort

Teams from the U.S., Canada, France and Britain had spent days scanning a vast expanse of open sea for the Titan.

The U.S. Coast Guard’s Mauger said it was too early to say when the Titan met its fate.

The position of debris relatively close to the wreck suggested it happened near the end of Sunday’s descent.