Which Gases are Used in Diving?
The following is a list of Gases which can be used in breathing mixes for diving:
Air is 21% oxygen and 79% nitrogen. It is readily available and cheap. Nitrogen narcosis can occur when breathing air. Narcosis or "Rapture of the Deep" can be noticed at about 30m and air should definitely not be used beyond 50m!
This is the main element needed to sustain life. However, it is flawed because too much or too little of this necessity is toxic! At a a partial pressure greater than 2 bar, oxygen is toxic. Below 10m, pure oxygen starts to become dangerous. The dangerous partial pressure for oxygen in air is reached at about 70m.
Nitrogen is inert and it makes up 79% of air. As the partial pressure of nitrogen in a breathing mixture increases, its narcocity increases. Upon descent, the nitrogen in the mixture dissolves into the body tissues. If ascent is too rapid, the bubbles come out of the tissues too rapidly for the body to handle efficiently thus causing decompression sickness or "The Bends".
This is any mixture of oxygen with nitrogen. This mixture allows the diver to have longer dives with fewer and shorter decompression times. This however, does not allow the diver to go deeper!
Helium is also inert and can therefore replace nitrogen in breathing mixtures. Because Helium is not toxic, Heliox is used for deep diving and saturation diving. Decompression is still needed when using Heliox but due to its size, the bubbles leave the tissues faster thus reducing the decompression times. Helium conducts heat more rapidly than air, therefore a diver will lose heat more rapidly.
Trimix is a mixture of oxygen, helium and nitrogen.
Neon is found to be a good alternative to Nitrogen as an inert gas. Experiements have been done up to 366m and no narcosis was found. However, due to its large size Neon is harder to breathe than Helium at depth.
This gas is physiologically inert and hence is very ideal, especially for deep diving. It is more narcotic than helium and neon but less narcotic than nitrogen. The only disadvantage is that Hydrogen is explosive in mixtures of more than 4% oxygen.
So...Why are some gases used and how?