You see alot of information regarding percentage of O2 used in nitrox and trimix, along with reasons as to what is good/bad, but I can't find zip for helium.
Speaking strickly normoxic, there appears to be some fairly "standard" mixes floating about; 20/40, 30/30, 25/35 and maybe a couple others, but I cannot find anything on WHY its 30/30 and not 30/50, or 20/50 instead of 20/40. Realizing cost of He being what it is most places, and discounting that, are there any defined guidelines out there?
In the "lessor" trimix depth ranges (<200ft) the percent of He has an effect on deco time, but not significant once you have to be there, as it where. IOW, once you have to deal with 40% He, going to 50% doesn't appear to make much difference.
I have also seen reference to GUE standard mixes, but the little I have gotten from that is they are more for uniformity, and possilbly ease of mixing/storage than anything.
So, is the He percent more how much ya gotta pay for it, or is there some good reasoning behind what % to use?
Phil
Speaking strickly normoxic, there appears to be some fairly "standard" mixes floating about; 20/40, 30/30, 25/35 and maybe a couple others, but I cannot find anything on WHY its 30/30 and not 30/50, or 20/50 instead of 20/40. Realizing cost of He being what it is most places, and discounting that, are there any defined guidelines out there?
In the "lessor" trimix depth ranges (<200ft) the percent of He has an effect on deco time, but not significant once you have to be there, as it where. IOW, once you have to deal with 40% He, going to 50% doesn't appear to make much difference.
I have also seen reference to GUE standard mixes, but the little I have gotten from that is they are more for uniformity, and possilbly ease of mixing/storage than anything.
So, is the He percent more how much ya gotta pay for it, or is there some good reasoning behind what % to use?
Phil