It's also a deco dive. Even the first one. Or at least it is in my universe.
Dec to 75ft (1) Nitrox 32 50ft/min descent.
Level 75ft 73:30 (75) Nitrox 32 1.01 ppO2, 58ft ead
Asc to 20ft (76) Nitrox 32 -30ft/min ascent.
Stop at 20ft 12:10 (89) Nitrox 32 0.49 ppO2, 10ft ead
Surface (89) Nitrox 32 -30ft/min ascent.
Off gassing starts at 43.3ft
OTU's this dive: 76
CNS Total: 25.0%
154.5 cu ft Nitrox 32
154.5 cu ft TOTAL
What size tanks are you using to get 75 minutes at 75 feet ?
I stand by my crappy answer.
Hi ianr33, thanks for the reply. Correct, you are in your universe with your assumpitions, and I am in mine. You should take care in generalization.
I dive EAN36 to an average depth of about 60 feet for 75 minutes. My CNS exposure is 25%. I'm diving the DSAT algorithm without conservative factor. This is not close to the NDL of 2:04. I make these dives with an AL80. My average SMRV is 0.30-0.33. I surface from my drift dive with about 500 psi, or slightly less.
It's not difficult to make 4 dives like this per day, 2 in the morning with a reasonable SI and 2 in the afternoon after coming in for lunch. Throw in 1 or 2 slightly deeper dives and you may increase your oxygen exposure. Add a 5th dive and the exposure is increased. Multiple days do add to your exposure because you are adding additional dive time onto the previous day prior to clearing the 24 hour period.
Realizing my problem with oxygen exposure, I have switched from EAN36 to EAN32 for my usual local dives. Some of my dives are now deco limited and my total dive time is somewhat decreased, but I rarely approach 100% of my CNS oxygen exposure. There's an important lesson here, everyone diving nitrox should be aware of oxygen exposure and its basis, not only the partial pressure limits, but the exposure over time.
I'd still like to know if some computers give oxygen surface interval credit. It's my impression that this is generally not taken into account for recreational diving.
Good diving, Craig