The estate of a French explorer killed along with others in the implosion of the deep-sea submersible Titan last year has sued the company that built it and embarked on the deadly trip to the Titanic wreckage.

The lawsuit, filed by the administrator of the estate of Paul-Henri Nargeolet in Washington state, names that company, OceanGate Inc.; the estate of its co-founder and CEO, Stockton Rush; and other companies. It seeks more than $50 million.

It argues Rush used carbon fiber for the craft’s hull, a material not previously used in submersibles; that he refused certification that could have provided the outside expertise that could have prevented the tragedy; and that those aboard most likely would have known they were about to die.

Nargeolet, Rush and three other people died when the submersible, which was attempting to reach the wreckage of the Titanic, imploded in June 2023. One of the dead was 19 years old.

“Nargeolet may have died doing what he loved to do, but his death — and the deaths of the other TITAN crew members — was wrongful,” says the lawsuit, filed Tuesday in King County.

“The catastrophic implosion that claimed Nargeolet’s life was due directly to the persistent carelessness, recklessness and negligence” of OceanGate, Rush and the other defendants, it says.

The lawsuit alleges OceanGate and others ignored warnings from deep-sea diving experts and engineers about the Titan.The suit argues that modern commercial crewed submersibles for deep-sea exploration are generally made from titanium — but that Rush believe titanium was unnecessarily heavy and directed that the hull be made from carbon fiber.

Rush also declined to have the sub certified by DNV, a classification organization that advises the maritime industry on safety.

Because of that choice by Rush, “there were no independent or third-party sources for information or assurance” before the fateful voyage, the suit says.

It was not immediately clear Wednesday whether OceanGate had an attorney representing it in the civil suit. The company’s website lists no contact information, and it has a message that reads “OceanGate has suspended all exploration and commercial operations.”

The disappearance of the sub on June 18, 2023, sparked a frantic search to rescue its crew, and multiple countries sent resources to help the U.S. Coast Guard-led effort. The Coast Guard eventually said debris had been located, and human remains have been found and returned to land.

The Titan had been trying to reach the wreckage of the Titanic, which is on the sea floor of the Atlantic Ocean, around 12,500 feet, or 2.3 miles, deep.

Nargeolet was an experienced diver known as “Mr. Titanic,” and he had completed 37 dives to the famous wreckage over his career. OceanGate hired him to help guide the Titan at the wreckage site because of his familiarity with it, the suit says.

OceanGate suspended all exploration and commercial operations after the disaster.

The Coast Guard opened a Marine Board of Investigation into the implosion to determine its cause. A public hearing is scheduled for Sept. 16.Also killed in the implosion were British billionaire Hamish Harding and prominent Pakistani businessman Shahzada Dawood and his 19-year-old son, Suleman.

The lawsuit also alleges the chilling detail that the crew would have been aware that the sub was about to implode.

Carbon fiber makes a crackling noise under pressure, and Rush installed an “acoustic safety system” that would detect that crackling and alert the pilot, the lawsuit says.

“While the exact cause of failure may never be determined, experts agree that the TITAN’s crew would have realized exactly what was happening,” the suit says.

“RUSH’s vaunted ‘acoustic safety system’ would have alerted the crew that the carbon-fiber hull was cracking under extreme pressure — prompting the pilot to release weight and attempt to abort,” it says. “Common sense dictates that the crew were well aware they were going to die, before dying.”

The suit says that the amount of damages is not precisely known but that it is at least more than $50 million.