Dear Pete:
Yes, the use of the
inert gas diluents is to reduce the partial pressure of oxygen while at the same time acting as a
counter pressure to the weight of water. (Many divers do not realize that the ability of our chest muscles to expand the thoracic cavity, and the lungs, at depth is what requires us to use compressed gas in the water. If we had super strong chest muscles, we would not need the counter pressure of the breathing gas.)
People over the years have investigated different inert diluents for diving. It is necessary that the gases are inert in the body, or, if they have an effect, it is not untoward. The inert gases (sometimes called the rare gases, although
argon is not rare at all) are narcotic to some degree, with the exception of helium. We are all aware that the narcotic property of gases such as nitrogen is quite high at moderate pressure; a gas such as nitrous oxide (the laughing gas used in a dentists office) is narcotic at atmospheric pressure. :loopy:
Since the gases are inert under conditions of the bodys temperature and pressure, they do not form any reactive compounds. However, that does not necessarily make all of the inert gases suitable for diving. Let us look at these.
- HELIUM was first discovered on the sun :fire: by astronomers using a spectroscope (the glass device that breaks up light into the colors of the rainbow). The gas was soon discovered in natural gas wells in the southwest part of Texas (the gas from the wells burned poorly), and it was introduced into diving because it was poorly soluble and did not produce narcosis. It has a bad effect on speech (the Donald duck voice) and causes the loss of heat from a divers body. It is not very soluble in adipose (= fat) tissue.
- NEON was investigated as a diving gas at the Ocean Systems, Inc., laboratories when I was there in the early 1970s. (Bill Hamilton, PhD, known to many recreational divers, was the Principle Investigator on that project.) This gas is similar in decompression characteristics to helium, but it has less speech distortion and the heat loss is reduced. Its main advantage was that it was available throughout the world (as a helium/neon mixture), being derived from air (by fractional distillation) in the production of oxygen for industrial purposes.
- ARGON is not suitable for diving because of its high lipid (= fat) solubility. This gas (in addition to being somewhat narcotic) will produce too many gas bubbles in the adipose tissues of the body. These are then released into the venous return (= the veins) where they can then flow to the lungs. Because so many bubbles are produced, in many cases the bubbles pass the lung capillaries and enter the arterial circulation (arterialization). This then leads to a (vein-to-artery) stroke, the so-called cerebral gas embolism.
- HYDROGEN was used as a diving gas, because it has a worldwide availability and was less costly than helium. It is a good gas for decompression, but its flammability requires that special handling be observed.:mean:
We can see that there are many different reasons that gases can be employed in diving situations, not all of them related solely to their inertness, but often for reasons of economic importance and availability.
__________________
Dr Deco
