Covering more than 70% of the world’s surface and with an average depth of 4km, the sum of man’s exploration and colonisation of our own oceans can be compared with our current success in colonising our own galaxy. For both quests it’s still “early days”.
So what’s holding mankind back from being able to exploit this last block of untouched real estate the world has to offer?
Air – The breath of life
From the moment we were born, our incessant desire to breathe air has tied us to the surface environment and fundamentally limited all excursions into the underwater realm dating back over the last 5,000 years.
The painful progress in discovering that air is not the best choice of breathing gas when undergoing either extremely deep or long term underwater excursion, was paid for directly with the lives of the many research divers hitting the seemingly arbitrary and unpredictable physiological limits of both air and other prospective breathings gases tried with varying degrees of success during the last century.
That the body is sensitive to the partial pressure of the constituent gases and not the percentage gas present in a particular mix leads to some strange observations. Oxygen, the most important gas, and absolutely necessary for life, must be present within quite a narrow range of partial pressure from 0.18-0.50bars for saturation diving exposure. Nitrogen can be disposed of entirely and replaced with another physiologically inert gas such as helium to yield Heliox, and the explosive gas hydrogen can be breathed at extreme depths, providing its own debilitating effects are compensated for by the helium. The deepest ever dives where the diver breathed Hydreliox (hydrogen/helium/oxygen mixture) achieved 701 metres depth during the COMEX Hydra 10 experiment in 1992.
The depth record established by COMEX represents the deepest depth that humans will likely ever breathe gas underwater. The gas Hydreliox is the lightest possible mix, and even with this mix, only one exceptional diver was able to sustain the breathing effort necessary to utilize this mixture at 71 bars/1,030 psi pressure.
Breathing gases are only part of the problem though. The human body’s compression and decompression requirements would likely require approximately one week to get the diver down to this depth, and a further one month spent in decompression to return him back to the surface symptom free.
So where does this leave us with respect to exploring the ocean depths beyond 700 metres?
For this task, some entirely different and radical approaches are necessary.
Bypassing the Limits
“To breathe or not to breathe, that is the question”
Popularised in the 1989 hi-tech diving film The Abyss produced by James Cameron, the concept of liquid breathing using oxygen enriched perfluorocarbon solutions such as Freon has been around since the 1960’s.
In the film, an actor is shown donning a deep diving suit that was apparently entirely flooded with the solution. Although this scene was a special effect, in another sequence, a mouse is submerged in the fluid to demonstrate it’s effectiveness as a breathing solution. This really happened: in the filming the poor mouse actually breathed liquid.
So why not humans breathing from a liquid? There are a number of problems, not least of which is the lungs’ sensitivity to having a potentially irritating chemical solution upsetting the delicate surfactant mucus that normally lines the internal surface of the lungs. There are other complications, such as the poor solubility of carbon dioxide in the breathing media, issues with the effort required to inhale and exhale the liquid, plus other impurities causing additional lung problems.
Perhaps the answer then, is just to stop breathing
The as-yet unborn fetal child grows from an egg to a human being in the mother’s womb with entirely non-functioning lungs. The placenta, formed from the same egg cluster as the fetus, carries out the critical gas/nutrient exchange duties, ensuring that the fetus has sufficient oxygen to sustain development, that carbon dioxide is removed, that nutrients pass from the mother to the fetus, and that waste matters are removed.
In the case of fetal development, the baby sees the same dissolved gas partial pressures as the mother. So if the mother breathes air in an hyperbaric environment, then inert gas partial pressures will also saturate fetal tissue, potentially causing decompression sickness should a large reduction in ambient pressure occur.
At the outset then, a non-breathing solution to ultra-deep diving seems not to offer much hope. It took the visionary underwater pioneer Jacques Cousteau to point out the solutions to this and other problems and its seemingly unlimited applications in his elegant book The Ocean World. Jacques proposed that the diver be ‘plumbed into’ an external system via a major vein and artery, which took care of blood oxygenation, dialysis to remove wastes, a chemical scrubber to remove carbon dioxide, and, presumably, some means of adding glucose, minerals, and vitamins to keep blood sugar at optimum levels.
The benefits are potentially profound. Since no breathing takes place, then the workload limitation of breathing extremely dense hyperbaric gases would not apply. Since there is no uptake of inert gas in the system, then there would be no need for decompression. Further, since the system did not involve flooding the lungs with a chemical solution, then there should be no problem with the alveoli irritation that plagues liquid breathing techniques.
The one fly in the ointment was that to achieve sufficient oxygenation, the system would need to be ‘plumbed’ directly into the heart, similar to the fetal umbilical cord.
Although it would be impossible to consider either recreational or technical divers undergoing such radical and risky surgery to enable accomplish a task, a commercial diver looking at a one-year, US$1 million dollar contract might well be tempted!