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For what it's worth, we do some dives requiring air
breaks, like Wakulla, for example. With the longer bottom
times, like 90 minutes, I start the deco at 190 on air, and
hit my first nitox at 120. Somewhere around the second nitrox,
second stop (50 feet) we figure the exposure limit is hit. I
begin this stop with a twenty minute air break, although I
do not actually "break", I consider it the same as if I were
breathing the nitrox for deco purposes. I would use the back
gas, but I don't want to get light, since I will continue
with a five minute air session for every twenty of deco gas
thereafter. I have as many as three air bottles in the water
all of the time, but the most I ever used was two and one
half for a 7 1/2 hour deco. If I feel any symptoms of O2
taxicity, that is when I break to my back gas, and again,
I consider this the same as deco gas for decompression
purposes. For longer bottom times, the breaks start deeper,
and have to be done on the back gas to get the PPO2 low enough
to matter. It is during these breaks that I do my light exercise,
swimming around with both hands and feet to get the circulation
going a little. The last long dive I did there, the B Tunnel
dive where we added 1820 feet was 84 minutes bottom at 300,
and we did an even five hours of total deco, used 2 1/2 airs,
one 35%, 1 1/2 50%, 1/1/5 o2, and 100 psi of back gas (felt bad
one time). For bottom gas we used two and one ha;f 80's, and
1600 psi back gas. No bends, no symptoms, not even tired. Drove
home the next morning and went diving. -= George
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