Posted by CalAbDiver on August 21, 2001 at 10:27:38:
In Reply to: Heli-air subject revisited posted by bbc on August 21, 2001 at 08:32:27:
thats the most i have read on it anywhere!
yes, i agree, it does seem more "natural" to simply add He to air, rather than mix O2, He, and N2. especially since the primary objective is to dilute the narcotic effect of the N2 and the toxicity potential of the O2, and adding He to air does this perfectly at the same time.
regarding a single deco bottle, i think i would always want to have two deco bottles, because that way they would balance each other on either side of your B/C, and one could be a thinner mix of O2, say EAN42 with its ppO2 of 1.6 at 90 fsw, and the other richer at say EAN84 with its ppO2 of 1.6 at 30 fsw.
this way you could dive as deep as 300 fsw on 50/50 Heli-Air [10.5/50/39.5] because the ppO2 at 300 fsw would be 1.05 and the EAD for N2 narcosis and deco purposes would be 137 fsw. So you could use the Navy 140 fsw table for planning NDL and deco times. and you could deco off the Heli-Air at 150 fsw to 100 fsw, and using the EAN42 at 90 fsw to 40 fsw and the EAN84 at 30/20/10 fsw.
i have just finished reading 3 TDI manuals and working through all the problems, before we begin the first of 8 deep training dives, and that is where my thinking currently is about Trimix and Heli-Air.
thanks for your post!