The main question is on of effect of changing the composition of breathing gas mixture. When breathing a mixture 10% Oxygen 8% nitrogen and 82% Helium at saturated levels, will there be an effect if we swap to 10% 0.5% Nitrogen 89% Helium as a breathing medium for 8 hours with upward excursions of up to 1.4b differential? My argument is it would be more beneficial to maintain levels as constant as possible to avoid diffusion and counter diffusion during extended changes either + or - 1.4 bar changes during saturation dives involving changes in storage depth during a saturation dive.

  • What are you actual considerations for effectively replacing nitrogen with helium (heliox instead of trimix?) The helium penalty is discussed e.g. here: shearwater.com/monthly-blog-posts/eliminating-helium-penalty nitrogen is added to trimix because of cost factor, so you want to have as much nitrogen as possible within your safety constraints Oct 21, 2021 at 10:16
  • Heliox saturation diving so Ideally Helium and oxygen. In the chamber envirnoment there is introduced Nitrogen form initial pressurisation ie 1 atmosphere aditional compressions using Pressure locks We reclaim this gas in general oporations cleaning out Co2 and other contaminants this reclaimed gas can contain up to 700mb of N2 with a maximum of 800mb allowable. The reclaimed gas is is used in Divers breathing gas in dives feeding a diver semi closed circuit system scrubbing out Co2 and adding Oxygen to maintain the required 5-800mb O2
    – Sam Dalton
    Oct 23, 2021 at 6:44
  • 1
    Not really a SCUBA diving question; certainly not recreational scuba. Aren't most saturation dives with that gas profile about 100m/330ft and using "surface supplied" gas, i.e. umbilicals? This isn't really Self-Contained-Underwater-Breathing-Aparatus (SCUBA)
    – GlennG
    Dec 5, 2021 at 13:05

1 Answer 1


No true but it is breathing gas from a pressure source so no difference in the technical question of physiologically effects of gas composition and decompression / pressure differential changes.bTissue saturation obviously is a factor that will differ as scuba is still in the gas uptake phase rather than saturated bug you can say saturation at baseline is one atmosphere as opposed to say 10 atmospheres.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.