Why scuba drivers use mixed gas cylinder during diving.
Why don't they use pure oxygen cylinders containing only oxygen
Answers
Answer:
a) Divers breathe compressed air and not pure oxygen. (Yes they sometimes do breathe pure O2, but only qualified divers who know the risks associated with it and used under limits - details later)
b) Compressed air is essentially 21% oxygen. Now in scuba diving we deal with partial pressures instead of percentages. So at atmospheric pressure, the partial pressure of O2 is 0.21.
Scientifically it has been found that a partial pressure of more than 1.4 for O2 (1.6 in some cases) is toxic and on the lower side the human brain needs a minimum partial pressure of 0.16 to sustain.
If we use these numbers, we can see that using 21% mixes can be safely used only to a certain depth (accurately 56.67 metres). So if you would want to go deeper, you would decrease the concentration of O2, keeping it within the partial pressure values of 0.16 and 1.4~1.6.
Now all gases have a narcotic effect at depth. Nitrogen has been statistically proved, Oxygen is assumed and almost set to be proved. This is due to the solubility of gases in the lipids, and long story short the presence of gases creates breaks in our neural synapses. So how do we tackle this situation. We cannot use higher amount of nitrogen in our gas mixture, and we cannot substitute nitrogen by oxygen at deeper depths. So we insert an inert gas into the mix to take both of their places. Helium is also narcotic at depth, but the depths to factor that in are very high. The presence of helium allows us to keep the O2 partial pressures to not become toxic and also keep the partial pressures of both O2 and N2 under their narcotic levels.
The data and text I have mentioned here, is based on my understanding of the subject and discussions with other divers. This should not be treated as an exhaustive source of information, and under no condition should you go dive with the information presented in this text.
Diving with mixes such as enriched air, trimix, heliox and other hypeproxic or hypoxic mixes require a lot of training and understanding of the human physiology. Please do not undertake any form of diving without having proper training. Normally regular recreational divers will not need to use anything more than a 40% mixture of Oxygen in their breathing gas.
Answer:
Diving with pure oxygen deeper than 20 feet can cause a person to absorb more oxygen than his system can safely handle, leading to central nervous system (CNS) oxygen toxicity. CNS oxygen toxicity causes a diver to go into convulsions (among other things).The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen below those of air, to allow the gas mix to be breathed safely on deep dives. ... Helium has very little narcotic effect. A lower proportion of oxygen reduces the risk of oxygen toxicity on deep dives.
Explanation:
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