Ed Harris' character in The Abyss in the process of removing his Liquid Breathing Diving Rig. Image copyright Twentieth Century Fox.

Liquid Breathing Rigs
Tech Level: 13

Liquid breathing is also sometimes called fluid breathing.

Liquid breathing technology replaces gas mixtures with a highly-oxygenated liquid that allows humans to continue breathing where the use of gasses might be detrimental. It is use for a number of medical procedures, particularly with premature babies, and has also been proposed for future spacecraft to help offset some complications from very high accelerations.

It is probably most famous, however, as an experimental means of diving to extreme depths without the usual detrimental pressure effects. It is the latter application this article will focus on.

Liquid breathing was first experimented with in the 1960s and tested successfully on animals since. A liquid breathing rig was prominently featured in the science fiction movie The Abyss. That film also contains a key scene of a rat shown surviving in PFC liquid; the scene was not special effects and the rodent was indeed actually breathing the liquid.

At the heart of the system are peflourochemicals, also called perflourocarbons or PFCs, which have the unusual property of allowing a very large percentage of gas solubility. In fact, these liquids can hold up to twenty-five times more dissolved oxygen and other gasses that human blood. In liquid breathing diving, the diver allows his lungs to be saturated with this oxygen-rich PFC liquid in place of air. Despite the PFC being heavier and more viscous than the normal gasses the diver would breathe, the lungs can still function normally.

With this system, the body can more easily equal adapt to the pressure of the surrounding water. Because of this, complications such as inert gas narcosis (from using either nitrogen or helium at too great a depth) can be minimized or eliminated altogether. Because narcosis is not a danger with liquid breathing rigs, there would also be little need for compression and decompression procedures. Under ideal conditions, some think that liquid diving rigs could carry divers down to depths of 1000 meters or so, compared to the extreme limit of 100 meters for gas mixture rigs.

However, there are many complications to the system. These type of diving rigs depend on Total Liquid Ventilation (TLV), which is a type of artificially-induced respiration where the rig takes over the breathing mechanics for the diver. These devices would be very similar to the artificial respirators currently used in hospitals, but much more compact and rated for liquids. The PFC liquid would be too dense for the diver to respire on his own for more than a few minutes before he began exhausting himself. Natural respiration would also be too slow, as the PFC liquid is not as efficient at carrying away CO2 as normal air. At normal breathing rates the user could still end up eventually suffocating.

So the TLV systemís precision pumps maintain a steady, rhythmic flow in and out of the lungs via tubes inserted into the trachea. It would also monitor the diverís condition to adjust the flow depending on his level of activity and needs. The PFC liquid is warmed to a comfortable temperature, and oxygen is saturated into the system from a reserve tank. Carbon dioxide and other waste gasses are filtered out. Higher Tech Level systems could replace some or all of the oxygen tank with an oxygen-cracking artificial gill system, lightening the rig but also using considerably more power.

Needless to say, this kind of system can be very uncomfortable for a diver not used to it. He not only has to endure liquid-filled lungs, a sensation that would be very reminiscent of drowning, but a tube that extends down his throat into the trachea. Even with the option of using mild drugs to suppress the gag or panic reflexes, using the liquid breathing rigs would still probably take very extensive training.

As the PFC liquid can be continually re-oxygenated and the system can recycle used gasses, a liquid breathing rigís endurance would probably be comparable to a gas mixture rebreather system. In other words, it would be able to keep its diver alive probably as long as the system was supplied power. In the original experiments in the 1960s, rats were able to survive up to 20 hours breathing PFC liquid. However, because the more viscous PFC liquid requires much more energy to move than air, it may wear away portable power supplies more quickly than gas mixture systems.

These kind of rigs would be heavier and more expensive to manufacture and maintain than normal diving equipment, but would still be cheaper than extreme depth equipment such as hardsuits and deep diving subs. They may in fact find their niche in operating in the middle territory between the lower limits of safe gas mixture diving and depths where more heavily robust systems start becoming a necessity, say between 100 and 800 meters. They would likely never be used to push toward their depth limits for safety reasons, except in emergencies.

From the film The Abyss, a pet rat is used to demonstrate liquid breathing technology. This scene was not a special effect; the rat was actually breathing PFC liquid. Image copyright Twentieth Century Fox.


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Article added 9 December 2010