Rescue workers are stepping up efforts to find missing vessels en route to the Titanic wreck

With alarms rising and air supplies aboard the missing vessel dwindling, a growing number of international rescuers on Tuesday stepped up their search for the five-people submarine that disappeared on Sunday while en route to the wreckage of the Titanic.

US Coast Guard commanders described a complex and very challenging search mission over an area the size of Connecticut some 900 miles off Cape Cod in the North Atlantic. Officials said it was complicated by the vast distances ships have to travel to get to the site, and the logistical complexity of a combined surface and underwater search for the privately owned 22-foot submarine, named Titan, that disappeared while diving. . two and a half miles deep to view the sunken ship.

“We’re doing everything we can,” said Captain Jamie Frederick, response coordinator for the First Coast Guard District, based in Boston. He estimated Tuesday afternoon that the five people on the submarine still had 40 hours of breathing air left.

But as the Coast Guard continued its “unrelenting effort” to find the lost Titan, troubling questions surfaced about the safety practices of the company that built it, OceanGate Expeditions. In a letter sent to the company’s CEO, Stockton Rush, in 2018, industry leaders warned of potential “catastrophic” problems due to the “experimental” approach and failure to follow established safety guidelines. The company, based in Everett, Washington, argued that such regulations hindered innovation.

“The letter was basically asking them to do what the other submarines are doing,” said one of the signatories, Bart Kemper, a forensic engineer.

Mr. Rush, the ship’s pilot, was among those missing. Others include Hamish Harding, 58, a British explorer; Paul-Henri Nargeolet, 77, a French marine expert who has made more than 35 dives to the Titanic wreck; a British businessman, Shahzada Dawood, 48, and his 19-year-old son, Suleman.

Mr Harding, who previously set a Guinness World Record for deep-sea diving, had recognized in the past how dangerous deep-sea exploration was.

“If something goes wrong, you’re not coming back,” he told an Indian news magazine in 2021, after his record-breaking trip to the Mariana Trench, seven miles deep in the western Pacific.

Search crews hampered by dense fog on Monday got better visibility on Tuesday, a Coast Guard spokesman, Petty Officer Robert Simpson, said. But some ships steaming to the area, including one from France equipped with a reconnaissance robot that can dive to 4,000 feet, had to travel three or four days to reach the site, he said.

Another Royal Canadian Navy ship en route Tuesday is equipped with a hyperbaric recompression chamber, which is used to treat diving-related ailments.

The Titan is classified as a submarine and not a submarine, as it is not autonomous and requires a support platform to deploy. It’s built of titanium and carbon fiber, weighs about 21,000 pounds and provides 96 hours of “life support” for five people, according to the OceanGate website.

The submarine has been missing since Sunday, when it lost communication with the Canadian research vessel MV Polar Prince, prompting it to deploy. The last communication was about an hour and 45 minutes, according to the Coast Guard.

But even that narrow 96-hour window for survival may be too generous. Some experts have questioned whether travelers could survive that long, citing the risk of carbon dioxide buildup in the submarine if it isn’t equipped with a system to remove it.

Rachel Lance, a biomedical engineer at Duke University who has studied submarine disasters and built underwater breathing systems, said she had seen no evidence of such a system in publicly available photos of the Titan’s interior.

Without carbon dioxide removal, she said, the survival limit for people indoors would likely be closer to “one or two days, at most, for five people in such a small space.”

Dr. Lance said the U.S. Navy has established strict standards for carbon dioxide management in submarines after disasters such as HMS Thetis in 1939, in which 99 crew members died from carbon dioxide buildup.

“We learned these lessons,” she said. “You can’t buy your way out of safety measures and you can’t negotiate with respiratory physiology.”

A submarine traveling to the depths of the Titanic would experience massive increases in pressure during its long descent. At the ship’s resting place, it would experience a pressure equivalent to that under a 100-story tower made of solid lead – the height of the Empire State Building.

Founded in 2009, OceanGate Expeditions sought to increase access to deep-sea exploration by organizing expeditions for paying tourists to visit shipwrecks, part of a rising trend in high-risk excursions. The Titanic, which sank in the North Atlantic in April 1912 after colliding with an iceberg, killing 1,500 passengers, has attracted great interest since the discovery of the wreck in 1985, and since the 1997 blockbuster film the tragedy a new aura of romance.

In the early 2000s, scientists warned that visitors posed a threat to the wreck, saying that gaping holes had appeared in the decks, walls had crumpled, and rustics — icicle-shaped rust structures — were spreading all over the ship.

That reports the technical news site GeekWirethe Titan was “rebuilt” after OceanGate determined through testing that the ship could not withstand the pressure of a 12,000 foot dive. Trips to the Titanic started in 2021 and cost $250,000 per person.

Mike Reiss, a passenger who traveled on the same OceanGate voyage last year, told the BBC that the mission was an “adventure” and a “very serious expedition”, not a “tourist trip”. He said the submarine was small but comfortable – “spa-like” – but the people on board were well aware of the dangers. “You sign a waiver before you get in that mentions death three times on page 1,” he said. “It’s a beautiful, moving experience,” he added.

Numerous factors can hinder the ongoing rescue operation, including weather conditions, darkness, sea conditions and water temperature. For an underwater rescue, the level of difficulty is even greater than on the surface. But first, rescue teams must locate the submarine.

Many underwater vehicles are equipped with an acoustic device, often called a pinger, that emits sounds that can be heard by rescuers underwater. But it remains unclear whether Titan has one on board.

The US Navy has a submarine rescue vehicle, although it is said to be able to reach depths of only 600 meters. To recover objects from the seabed in deeper water, the Navy relies on what it calls remotely operated vehicles, such as the one it used to recover a crashed F-35 Joint Strike Fighter at about 12,400 feet in the South Pacific. China Sea in early 2022. That vehicle called CURV-21can reach depths of 20,000 feet.

Mr. Nargeolet, the French adventurer among the passengers of the Titan, who once served as a deminer in the French Navy, tried to explain in an interview last year why the mysteries of the Titanic beckon, despite the danger.

“Once you stick your head in the Titanic, it’s hard to get it out,” he said.

Reporting contributed by Anna Bets, Christine Chung, William J. Broad, Emma Bubola, Vyosa Isai, Jenny Gross, Ben Shpigel, Alan Yuhas, Amanda Holpuch, Anushka Patil, Jesus Jimenez, Aureline Breeden, Derrick Bryson Taylor, Salman Massood, John Ismay And Nicholas Bogel-Burroughs.