Just weeks before the Titanic tourist submarine vanished, a former US Navy member warned of the terrifying health implications of being imprisoned in a submarine. Dr. Dale Molé, the former director of undersea medicine and radiation health for the US Navy, described the ‘hostile’ environment on commercial submersibles in a paper that was published in a medical journal last month. Passengers could be exposed to low oxygen levels, toxic carbon dioxide levels, and subfreezing temperatures.

Although most ships have a restricted capacity, the Titan vessel, which is still missing, will feature a carbon dioxide scrubber on board to eliminate extra hazardous gas that accumulates as passengers exhale in the small space.

Due to the chilly temperatures in the ocean’s depths, hypothermia is also a possibility. Panic attacks can also cause hyperventilation, which can deplete additional oxygen.

Dr Molé’s paper was published in a scientific journal on May 29, just 20 days before the Titan vessel lost contact with its mothership, leaving five people trapped. The US Coast Guard estimates that the sub has only 40 hours’ worth of oxygen left.

In his paper, published in the journal Ciottone’s Disaster Medicine, Dr Molé said: ‘Trapped crew in a sunken ship or submarine face many physiological challenges, including toxic gases, exposure to elevated ambient pressures, and hypothermia.’

Dr Molé told DailyMail.com today: ‘Anytime humans are confined in an airtight space, most people may think of oxygen, but carbon dioxide is actually a bigger concern.

‘In a submersible, they’ll have some system of scrubbing carbon dioxide. If they lost battery power, then that system would no longer work.’

According to Dr. Molé, assuming the passengers are not already dead due to a “catastrophic rupture of the pressure vessel,” it is “very much” a race against time to save them.