As the search continues for a submersible vessel carrying five people when it disappeared on its way to the wreckage of the Titanic continues, rescuers are working against the clock.

Jeff Karson, a deep sea researcher, told NBC News conditions inside the Titan are likely cold and cramped, with just a single window through which to view the surrounding darkness.

Temperatures at the bottom of the ocean are just above freezing. That means that inside the sub is likely dripping with condensation, he said.

In addition, passengers could be dealing with hypothermia if the power has been out on the sub.

Ret. Navy Capt. David Marquet, a former submarine captain, told CNN the passengers are likely very uncomfortable.

“They’re freezing cold,” he said. “The water entirely surrounding the ship is at freezing or slightly below. When they exhale, their breath condenses. There’s frost on the inside of the parts of the submarine. They’re all huddled together trying to conserve their body heat. They’re running low on oxygen and they’re exhaling carbon dioxide.”

The biggest question, however, is how long will the oxygen last?

The U.S. Coast Guard projects that the oxygen supply on the Titan will run out at 6:08 a.m. (7:08 a.m. ET) Thursday, a spokeswoman said Wednesday.

OceanGate’s specs for the Titan submersible say it is equipped with 96 hours of oxygen.

The Coast Guard said around noon (1 p.m. ET) Tuesday that rescuers had 41 hours left.

Capt. Jamie Frederick, the First Coast Guard District response coordinator, noted that the five passengers on board the Titan have a “limited ration” of food and water, but it’s not clear how much.

The search for the missing submersible Titan has expanded to twice the size of the state of Connecticut, Frederick said Wednesday. The sub surface search is up to 2.5 miles deep.