[Brian of Aquanauts]

Firstly if I'm diving to that depth I'm using a deco bottle of 50%. I have a team around me and i wouldn't really want a narcotic depth of over 30m.

so at 45m 25/25 gives me an END of 31.25m and 21/35 an END 25.75m this alone would make me pick the higher helium %.

Now lets look at the differences in RT for 30 mins at 45m using Bulhmann with GF Low 30% and GH High 85%.

21/35 total RT - 63 mins
Depth Time O2
45 30 21
21 1 50
18 1 50
15 2 50
12 2 50
9 4 50
6 20 50
0

25/25 total RT - 58 mins
Depth Time O2
45 30 25
21 1 50
15 1 50
12 2 50
9 3 50
6 18 50
0

These figures are straight from decoplanner and I haven't adjusted them to what i would actually do but i think that you can see that the difference in RunTime is minimal, for the cost of a narcotic depth of nearly 6m deeper. Also the ppO2 at depth for 25/25 is 1.375 this is way to close to the absolute maximum I'm comfortable working with at depth and so is a little hot for my liking. I prefer to plan for max 1.2 ppO2 allowing a nice contingency of up to 1.4 if needed.

So all in, i'd choose 21/35, for lower narcosis, lower ppO2, and only a minimal cost in terms of deco time.

Re your lost deco gas... i'd just multiply each stop time by 1.5 and share my buddies gas doing half the time on the gas each and the other half on back gas. remember that we always train in teams, and separation is not an option in a well trained team.

Others would pick a different solution, but I like keeping things simple and the standard gases do that for me.