Safety fears had previously been raised about the deep-sea vessel which went missing on a dive to the Titanic shipwreck.
The submersible, named Titan, lost communication with tour operators on Sunday while about 435 miles south of St John’s, Newfoundland, during a voyage to the shipwreck off the coast of Canada.
Titan has five people on board, including British billionaire adventurer Hamish Harding, and on Tuesday the US Coast Guard estimated the 6.7 metres (22ft) long OceanGate Expeditions vessel had just 40 hours of oxygen left.
The others on board are Shahzada Dawood, his son Suleman and OceanGate’s chief executive and founder Stockton Rush, reportedly together with French submersible pilot Paul-Henry Nargeolet.
It is understood the King is being kept informed of the search efforts, as Shahzada Dawood is a long-time supporter of The Prince’s Trust International and The British Asian Trust, both of which are charities founded by Charles.
As the race to find the vessel intensified on Tuesday, it emerged a former employee of OceanGate had raised concerns over “safety and quality control issues regarding the Titan to OceanGate executive management”, according to court filings.
David Lochridge, OceanGate’s former director of marine operations, claimed in the August 2018 court document he was wrongfully fired after flagging worries about the company’s alleged “refusal to conduct critical, non-destructive testing of the experimental design”.
After “issues of quality control” with Titan were raised, the filings say Mr Rush asked Mr Lochridge to conduct a “quality inspection” report on the vessel.
During this process, Lochridge “identified numerous issues that posed serious safety concerns” but he was allegedly “met with hostility and denial of access” to necessary documents before later being fired.
The document claims he became concerned about a “lack of non-destructive testing performed on the hull of the Titan”, and that he “stressed the potential danger to passengers of the Titan as the submersible reached extreme depths”.
In a November 2022 episode of his Unsung Science podcast, CBS journalist David Pogue interviewed Mr Rush ahead of going on a Titan expedition to the wreckage.
In the podcast, Mr Rush told him: “You know, at some point, safety is just pure waste.
“I mean, if you just want to be safe, don’t get out of bed, don’t get in your car, don’t do anything.
“At some point, you’re going to take some risk, and it really is a risk-reward question.
“I think I can do this just as safely by breaking the rules.”
Mr Pogue also said he had signed a waiver before going on the dive which allegedly said: “The experimental submersible vessel has not been approved or certified by any regulatory body” and that the trip could result in death.
OceanGate has been approached for comment.
On Tuesday David Mearns, a deep-sea shipwreck hunter who is friends with Mr Harding and Mr Nargeolet, said he had seen reports of “tapping” being heard in the water, which he said could indicate the passengers are alive.
He told Channel 4 News: “There’s some reports that I’ve just read from my own club, which is how I know Hamish, is that somebody today has heard some tapping.
“Now they’ve got sonar buoys out there, there may be some other hydrophones that the mothership the Polar Prince had in the water.
“It’s hard to imagine how they could have heard that but still, they are at least trying to operate or encourage the rescue efforts to continue on and to be redoubled on the fact that they’ve heard something which suggests that the men are alive in the submersible.”
On Tuesday, Captain Jamie Frederick of the US Coast Guard said a “unified command” of multiple agencies was formed on Monday to tackle the “very complex problem” of finding the missing submersible, which has so far “not yielded any results”.
Speaking at a press conference in Boston, Captain Frederick estimated there was “approximately 40/41 hours” (of oxygen left) on the vessel, which started with 96 hours of breathable air.
Captain Frederick was non-committal when asked if there is any way to retrieve the submersible and save the five on board if it can be located.
“So, right now all of our efforts are focused on finding the sub,” he said.
“What I will tell you is we have a group of our nation’s best experts in the unified command and if we get to that point, those experts will be looking at what the next course of action is.”
He added: “On Sunday, the co-ordination command centre in Boston received a report from the Canadian expedition vessel Polar Prince of an overdue 21-foot submarine, Titan, with five people on board.
“The Titan was attempting to dive on the wreck of the Titanic, approximately 900 miles east of Cape Cod and 400 miles south of St John’s, Newfoundland.
“Approximately one hour and 45 minutes into the scheduled dive, the Polar Prince lost all communication with the Titan, Polar Prince conducted an initial search and then requested Coast Guard assistance.
“Since Sunday, the Coast Guard has co-ordinated search efforts with the US and Canadian Coast Guard, Air National Guard aircraft and the Polar Prince, which has searched a combined 7,600 square miles, an area larger than the state of Connecticut.
He said these efforts have involved aircraft searching by sight and with radar and sonar buoys, and that on Tuesday Deep Energy, a 194-metre pipe-laying vessel, with “underwater ROV (remotely operated vehicle) capability” had joined the search.
“To date, those search efforts have not yielded any results,” he added.
