How To Escape From A Submarine Stranded On The Sea Bed

(This is an updated version of a 2021 piece written after loss of the Indonesian submarine KRI Nanggala-402 off Bali, and confirmed that all 53 people on board were dead. The time taken to find it, with the tense countdown as the oxygen supply ran out, showed the need for submariners to rescue themselves from such incidents).

A submarine commander will attempt to surface their vessel as soon as trouble occurs, and the missing Titan submersible apparently has automated systems to do just that. However, in the event of a catastrophic loss of power, a submarine will usually end up stranded on the sea bed, with a limited oxygen supply. Escape is possible – but only under certain conditions.

The problem is the effect of extreme pressure on the human body. Atmospheric pressure at sea level is around 15 psi or 1 kg per square centimeter. Every ten feet/3 meters you go underwater add an atmosphere, exerting a crushing force which makes it increasingly difficult to breathe. Most scuba divers are limited to 60 feet, those with advanced qualifications and the right equipment can go to 130 feet. Professional divers can go below 200 feet, but this requires with helium-based breathing mixtures to avoid nitrogen narcosis – the pressure is so great that it forces nitrogen into the bloodstream producing something like drunkenness, with disorientation, euphoria and hallucinations.

Humans simply are not built to withstand these sorts of conditions.

The deepest unassisted submarine escape on record was by British submariner Bill Morrison in 1945 when his experimental midget submarine sunk in Loch Striven in Scotland after a collision. Morrison managed to force open an escape hatch and came up in a bubble of air. He remembers nothing about the ascent and surfaced unconscious and bleeding from his ears, nose and mouth. The bleeding stopped within the hour, and Morrison made a full recovery. In fact the only long-term health effects were pains in his head, neck and shoulders from forcing the hatch open.

Modern submarine deep escape systems are effective down to a maximum depth of 600 feet. Current U.S. Navy submarines are equipped with special air locks called escape trunks, each of which can release two survivors per cycle. The survivors, wearing escape suits, enter the trunk and the lower hatch is closed. Their escape suits are inflated to high pressure. The trunk then fills with water, and the escapers are released rapidly to minimize their exposure to the pressure, ascending rapidly in their inflated suits, breathing normally.

On the surface the escape suit – technically Submarine Escape Immersion Equipment – becomes a life raft which also protects the wearer from hypothermia. The suits are bright orange so survivors can be easily located.

The challenge is the rate of pressurization and how long a human can survive. In a 1987 exercise, 25 instructors carried out an escape from a record-breaking 603 feet. The flooding takes 24 seconds.

“The pressure doubles every four seconds,” instructor David Wadding said in an interview afterwards. “ I can assure you at deeper depths [from 300 feet to 600 feet in 4 seconds] that this is an extremely traumatic experience.”

The ascent to the surface takes up to four minutes from six hundred feet. This rapid and uncontrolled rise is more dangerous than the careful ascent by stages which scuba divers carry out. During the exercise there were several injuries, including perforated eardrums and ‘bends’ or decompression sickness in which nitrogen boils out of the bloodstream causing severe joint and bone pain.

The U.S. Navy is looking at an enhanced Deep Escape System which would almost double the current depth to over 1000 feet. A research contract was awarded to Vishwa Robotics which has previous worked with the Navy on robotics hands for an Atmospheric Diving Suit. This is effectively a one-man submersible which completely isolates the wearer from the surrounding water, and which are used for operations to 2,000 feet and below. However, these suits are huge, and the project notes that stowage requirements are a key factor, as space is highly constrained on submarines. In the case of something like Titan, the diving suits would probably occupy more space than the passengers.

One left-field approach to the challenge of survival under extreme pressure is liquid breathing. Air is compressible so your lungs tend to be crushed at depth, but if, like fish, you breathe an incompressible liquid the problem disappears. Water cannot absorb enough oxygen to be breathable by humans, so researchers used perfluorocarbon for liquid ventilation.

The technique was pioneered by both U.S. and Russian navy researchers in the 1960s but little information has ever been released. Commercial diver Frank Falejczyk was the first man to ever breathe liquid; Falejczyk later gave a presentation which was seen by James Cameron who used the extreme diving technique in underwater actioner The Abyss.

In the original 1968 tests of liquid ventilation on dogs, only 7 out of 22 survived the experience. The technique was refined before it was tested on humans but liquid breathing is extremely unpleasant. It requires the breather to fill their lungs up with liquid, effectively to drown, and there are strong reflexes working against this. Afterwards there is the challenge of getting the liquid out to breathe air, and some subjects have reportedly broken ribs in the violent coughing fits that this brought on.

Liquid breathing is, however, extremely effective at reducing the effects of pressure. Researchers brought animals from the equivalent of 1,000 foot depth to sea level pressure in one second, which would have been instantly fatal if they had been breathing gas, but with liquid ventilation there were no adverse effects.

Exactly how deep a human could survive with this technology is unknown, and the Russian equivalent of DARPA was reportedly working on this a few years ago. But in the case of the Titan we are not just talking about a few thousand feet, but a seabed depth of around 12,500 feet. (The Titan’s hatch is also secured with bolts from the outside, so external rescue would still be required).

For as long as there are crewed submarines there will be submarine accidents, and vessels ending up on the sea bed. Rescue technology will continue to improve, but escaping from even relatively shallow depths will still be a struggle against the odds.