Hi all,
Apologies in advance if this is all well-known useless cr*p...
During my AN&DP course my instructor mentionned in passing the factoid that in the recreationnal nitrox range the sum of the O2% and max depth for a 1.6bar ppO2 was 70-ish. Said it might be useful to sanity-check max depth on the boat for low O2% deco mixes (obviously everyone knows them for 50%, 80% and 100%).
Did the math on train this morning. It works because the sum, 100*fO2-10+10*ppO2/fO2 reaches a minima of Smin=20*sqrt(10*ppO2)-10 at fO2=sqrt(ppO2/10), and doesn't grow up too much around it.
So basically, for a ppO2 of 1.6bar, the minima is 70, at 40%, and the sum remains between 70 and 72 for a fO2 between 32% and 50%.
For a ppO2 of 1.4bar, it's 65 (64.8), at 37.4%, and the sum remains between 64.8 and 66.8 for a fO2 between 30% and 47%.
To sum up, in the specified range, you can quickly guess the MOD by just doing 70-O2% (1.6) or 65-O2% (1.4), and it will be a bit on the conservative side of things, by at most 2m (well, modulo 20cm at 1.4).
For instance:
1.6:
mix quick real
32%: 38m 40.0m
34%: 36m 37.1m
40%: 30m 30.0m
44%: 26m 26.4m
48%: 22m 23.3m
50%: 20m 22.0m
1.4:
mix quick real
30%: 35m 36.7m
32%: 33m 33.8m
35%: 30m 30.0m
36%: 29m 28.9m
37%: 28m 27.8m
38%: 27m 26.8m
39%: 26m 25.9m
40%: 25m 25.0m
43%: 22m 22.6m
44%: 21m 21.8m
47%: 18m 19.8m
Now obviously everyone has properly marked cylinders, knows his or her MOD and dives with a Nitrox/Trimix computer that they know how to use and have actually set up properly, but maybe in the real world...
Thoughts?
Cheers,
Matthieu
Apologies in advance if this is all well-known useless cr*p...
During my AN&DP course my instructor mentionned in passing the factoid that in the recreationnal nitrox range the sum of the O2% and max depth for a 1.6bar ppO2 was 70-ish. Said it might be useful to sanity-check max depth on the boat for low O2% deco mixes (obviously everyone knows them for 50%, 80% and 100%).
Did the math on train this morning. It works because the sum, 100*fO2-10+10*ppO2/fO2 reaches a minima of Smin=20*sqrt(10*ppO2)-10 at fO2=sqrt(ppO2/10), and doesn't grow up too much around it.
So basically, for a ppO2 of 1.6bar, the minima is 70, at 40%, and the sum remains between 70 and 72 for a fO2 between 32% and 50%.
For a ppO2 of 1.4bar, it's 65 (64.8), at 37.4%, and the sum remains between 64.8 and 66.8 for a fO2 between 30% and 47%.
To sum up, in the specified range, you can quickly guess the MOD by just doing 70-O2% (1.6) or 65-O2% (1.4), and it will be a bit on the conservative side of things, by at most 2m (well, modulo 20cm at 1.4).
For instance:
1.6:
mix quick real
32%: 38m 40.0m
34%: 36m 37.1m
40%: 30m 30.0m
44%: 26m 26.4m
48%: 22m 23.3m
50%: 20m 22.0m
1.4:
mix quick real
30%: 35m 36.7m
32%: 33m 33.8m
35%: 30m 30.0m
36%: 29m 28.9m
37%: 28m 27.8m
38%: 27m 26.8m
39%: 26m 25.9m
40%: 25m 25.0m
43%: 22m 22.6m
44%: 21m 21.8m
47%: 18m 19.8m
Now obviously everyone has properly marked cylinders, knows his or her MOD and dives with a Nitrox/Trimix computer that they know how to use and have actually set up properly, but maybe in the real world...
Thoughts?
Cheers,
Matthieu