The ratio remains the same but the problem arises due to the physics of partial pressures.Originally Posted by sevorg
At 1 atmosphere there is roughly a partial pressure of 0.21 of oxygen and 0.79 of nitrogen.
At 2 atmospheres (eg 10 metres under water on scuba. 1 ATM of water pressure and the original 1 of air pressure) there is a partial pressure of oxygen of 0.42 and a partial pressure of nitrogen of 1.58.
Conversely at 0.5 atmospheres at altitude the partial pressure drops to 0.105 of oxygen and 0.395 of nitrogen.
The important thing is how the human body reacts to the partial pressures of these gasses. From memory a partial pressure of less than 0.16 of oxygen will result in a loss of consciousness and less than 0.12 may be fatal.
In diving we have to consider that both oxygen toxicity and nitrogen narcosis will occur as the levels rise,. This will result in convulsions and potential drowning from oxygen and irrational behaviour and potential drowning from nitrogen.
To combat these effects we accurately blend gasses to provide the correct partial pressures for the required depth of dive and will switch between different mixes on the descent and ascent.
It may be further complicated by wishing to increase the oxygen content of our decompression gasses to accelerate the process!
Stick to air in your guns, it's far less complicated! :-)
