Why 32% & 36%?

[rjack321]

a. NOAA 1 & 2 "support all no-deco dives?" What does that mean? As long as the dive time is short enough, even air will be a no-deco dive, right? Please explain to this poor guppy.

Thal can probably make more definitive statements but...

Scientific diving programs are not generally doing deco dives as we think of deco dives. They could do no stop dives (remember this is pre-safety stop being so widely used/accepted) or short deco dives with small amounts of backgas, non-accelerated deco. e.g up to a 5 or maybe a 10minute stop at 10ft.

Their concept of "light deco" was a little different than we'd use today. Otherwise it was all "no stop". Once the dive times got longer than "light deco" they'd be looking at chamber deco similar to the Navy. In water accelerated deco with multiple mixes was not part of NOAA's lexicon as I understand the history. Apparently they drew the boundary between lite and "too much" deco time at once a 20ft stop was required.

When NOAA I and II were "invented" nobody thought ppO2 1.4 was the MOD of anything, MODs were all ppO2 1.6

 

[lowviz]

.............a. NOAA 1 & 2 "support all no-deco dives?" What does that mean? ...............

Does section 2 in the link below help? I take it to mean that NOAA was intending to avoid gas switching at any point in the dive or decompression, as rjack321 just stated. It also gets close to providing the answer to your OP. (rounding the EAD deeper to the nearest 10' increment and use of existing tables) Table 1 shows that Nitrox II only shows a benefit in the 80-110' range. A couple % either way doesn't mean much when you go in 10' increments.

http://www.uphs.upenn.edu/ebdc/PDF/1994-10-30_CJL_Safety-Anal-NOAA-NitroxI-II-DCP-Tables.pdf

 

[lowviz]

................So it seems that the best guess answer is the 1.6 PPO2 at 40 meters = 32%. Hmmmm.

I'm going with bleeb and fdog. Table 1 (-see link in my previous post) shows an exact 10' reduction for Nitrox I and an exact 20' reduction for Nitrox II in the depth range of 80-110'.

How this is figured:
For each mix, calculate the EAD at 10' increments then promote (not round) these fractional depths to the next deeper even 10' value.

The next deeper 10' EAD depth is exactly the same as moving one row up (shallower) on the air table for Nitrox I and two rows up for Nitrox II. Picking 32% and 36% O2 results in an elegant simplification in a backwards sort of way.