The Missing 'Titan' Sub Will Run Out of Air Thursday Morning: 'This Is an Incredibly Complex Case'

The submersible, which was traveling to the wreckage site of the 'Titanic', had 96 hours of oxygen onboard when its dive began on Sunday

The missing Titan submersible is due to run out of air this morning.

According to BBC News, the sub's breathing air supply is expected to run out Thursday, June 22, at around 6:00 a.m. EST. The vessel had about 96 hours of oxygen onboard when its dive began on Sunday, United States Coast Guard officials said, according to CBS.

The U.S. Coast Guard admiral leading the search for the Titan told the BBC on Wednesday that the search team is operating under the assumption that they have around 20 hours left to find the sub.

"One of the factors that makes it hard to predict how much oxygen is left is that we do not know the rate of the consumption of oxygen per occupant on the sub," Rear Admiral John Mauger told BBC while speaking of the vessel, which was traveling to the wreckage of theTitanic when it went missing.

Mauger also told the outlet that he and his team had spoken to the five passengers' families directly about their search efforts.

Coast Guard Capt. Jamie Frederick said during a press conference on Tuesday afternoon that the vessel had "about 40 hours of breathable air left" based on the estimate that it had 96 hours of available oxygen when it was sealed.

Related: Billionaire's Text Emerges After 'Titanic' Sub's Disappearance as Concerns Over Vessel Mount

The sub is carrying five passengers and first went missing on Sunday, June 18, according to the First Coast Guard District’s official Twitter account. Per the BBC, contact with Titan was lost on Sunday as it made a more than two-mile descent to the Titanic wreckage site in the North Atlantic.

The search for the Titan began shortly after they “lost all communication” with Canadian expedition vessel Polar Prince “approximately 1 hour and 45 minutes” into the dive on Sunday, Frederick said.

Related: 'About 40 Hours of Breathable Air' Could Be Left on Missing 'Titanic' Sub, Official Says

Joe MacInnis, a renowned diver who has made two trips to the wreck of the Titanic, told CNN on Wednesday that the five passengers in the sub would be “resting, breathing as little as possible, and trying to keep calm” in order to conserve their energy.

The U.S. Coast Guard admiral leading the search for the Titan, which is operated by OceanGate Expeditions, confirmed on Wednesday that an aircraft with sonar buoys detected noise in the water on Tuesday.

“It’s a target, it's a focus for us to look at,” Rear Admiral John Mauger told CBS Mornings of the noises, though he added, “We don't know the source of that noise."

“This is an incredibly complex case,” Mauger continued when asked if he was optimistic about the rescue mission.

"As long as there is an opportunity for survival, we will continue to work and bring every resource to bear on the search,” he added.

The noises detected in the water have been described as “banging noises” per CNN. However, on Wednesday morning, the U.S. Coast Guard denied hearing the noises.

“We don’t have anything at this time indicating any implosion or banging,” U.S. Coast Guard Petty Officer 3rd Class (PO3) Briana Carter tells PEOPLE

Chris Brown, an explorer and friend of one of the passengers, told the BBC he believed the noises could have come from the sub.

"If you made a continuous noise, that's not going to get picked up, but doing it every 30 minutes, that suggests humans," he said. "I'm sure they're all conserving oxygen and energy, because it's cold and dark down there."

Aboard the sub was OceanGate CEO Stockton Rush, who was piloting the voyage; British-Pakistani businessman Shahzada Dawood and his 19-year-old son Suleman Dawood; and British billionaire Hamish Harding. French Titanic expert Paul-Henri Nargeolet was also aboard, PEOPLE has confirmed.

Nargeolet, known as PH, is a retired French diver with Navy experience. Submarine search and rescue expert Frank Owen told the BBC on Wednesday that Nargeolet would know what to do in this situation.

“On board this craft is a retired French navy diver," he said, per the BBC. "He would know the protocol for trying to alert searching forces… on the hour and the half hour you bang like hell for three minutes.”

Retired NASA astronaut Colonel Terry Virts shared the final text message he received from his friend Harding during an appearance on ITV’s Good Morning Britain on Tuesday, according to the New York Post.

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“Hey, we’re headed out tomorrow, it looks good, the weather’s been bad so they’ve been waiting for this,” the 58-year-old billionaire wrote, according to Virts, who said his pal undoubtedly “understood the risks” of the mission to explore the wreck, the Post reports.

“We talked quite a bit about the risks and the different things that they were going to be able to do,” Virts explained on the program, per the Post. “So he was very excited about it."

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