Nitrox 32 and 36
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OP
Thanks for the link. Very informative, even though I've only been able to read about half of it at the moment. I wonder if there is anyone around who was part of the testing/selection process.
I too found the history of enriched air fascinating. Here is a link to a DAN workshop that is rich in history and footnotes.
https://www.diversalertnetwork.org/files/DANnitrox_web.pdf
Additionally the NOAA dive manual 5th addition https://www.amazon.com/NOAA-Diving-...d=1517670679&sr=8-1&keywords=noaa+dive+manual Ch7 is on Nitrox diving ch 8 is on mixed gas. I was particular interested in hyperoxic mixed gas, Helitrox.
Personally I enjoy Helitrox within NDL, lots of threads on that to look at.
Enjoy
https://www.diversalertnetwork.org/files/DANnitrox_web.pdf
Additionally the NOAA dive manual 5th addition https://www.amazon.com/NOAA-Diving-...d=1517670679&sr=8-1&keywords=noaa+dive+manual Ch7 is on Nitrox diving ch 8 is on mixed gas. I was particular interested in hyperoxic mixed gas, Helitrox.
Personally I enjoy Helitrox within NDL, lots of threads on that to look at.
Enjoy
miked
Contributor
Great question!
For some reason that link will load for me.
Can anyone give a brief answer to the OP's question ?
IIRC, the instructor in my TDI nitrox class some 20 years ago, indicated that 32% was used because for a max PPO of 1.6 atm, the MOD (when rounded down for safety) was 130 ft., which was the maximum depth limit set for recreational divers.
I can't recall any similar statement regarding 36%.
Was the instructor correct, and what is the rationale at 36%?
Thanks in advance.
For some reason that link will load for me.
Can anyone give a brief answer to the OP's question ?
IIRC, the instructor in my TDI nitrox class some 20 years ago, indicated that 32% was used because for a max PPO of 1.6 atm, the MOD (when rounded down for safety) was 130 ft., which was the maximum depth limit set for recreational divers.
I can't recall any similar statement regarding 36%.
Was the instructor correct, and what is the rationale at 36%?
Thanks in advance.
Here is the article libnked to.
See pages 243-246.
The info you ask for is:
36 % Oxygen EAN
The selection of a "second-best all purpose" EAN mixture in support of field
operations was based on the need to provide the maximum possible bottom times for
scientists working in 60 to 110 fsw. NURC/UNCW has observed that many experiments
are performed around depth-related stations, the most common of which are 60 and 100
fsw. Because of tidal change and other considerations, the 100 fsw site is normally
somewhere between 95 and 105 fsw. The choices ofEAN mixtures to best cover this depth
range according to the N2I02 Mixtures for Optimizing Dive Time Table (Dinsmore, 1988)
are 35%, 36% or 37% oxygen mixtures. Comparison of the maximum no-stop bottom
times of these three mixtures (Figure 2) shows that each has certain advantages over the
others at various depth ranges. Generally, the 37% mixture is most advantageous in 70 - 84
fsw, 35% is unmatched in 115 - 118 fsw, and 36% is optimal in the 84 - 105 fsw depths.
NURC/UNCW's selection of 36% oxygen was based on two significant
observations: 1) the ability to provide the greatest number of optimum bottom times
throughout the 60 - 110 fsw range, and 2) the unmatched ability to provide 40 minutes of
no-stop bottom time at 105 fsw.
See pages 243-246.
The info you ask for is:
36 % Oxygen EAN
The selection of a "second-best all purpose" EAN mixture in support of field
operations was based on the need to provide the maximum possible bottom times for
scientists working in 60 to 110 fsw. NURC/UNCW has observed that many experiments
are performed around depth-related stations, the most common of which are 60 and 100
fsw. Because of tidal change and other considerations, the 100 fsw site is normally
somewhere between 95 and 105 fsw. The choices ofEAN mixtures to best cover this depth
range according to the N2I02 Mixtures for Optimizing Dive Time Table (Dinsmore, 1988)
are 35%, 36% or 37% oxygen mixtures. Comparison of the maximum no-stop bottom
times of these three mixtures (Figure 2) shows that each has certain advantages over the
others at various depth ranges. Generally, the 37% mixture is most advantageous in 70 - 84
fsw, 35% is unmatched in 115 - 118 fsw, and 36% is optimal in the 84 - 105 fsw depths.
NURC/UNCW's selection of 36% oxygen was based on two significant
observations: 1) the ability to provide the greatest number of optimum bottom times
throughout the 60 - 110 fsw range, and 2) the unmatched ability to provide 40 minutes of
no-stop bottom time at 105 fsw.
Rred
Contributor
"32% was used because for a max PPO of 1.6 atm,"
Could be time for a rethink on the mixture then, as 1.4 continues to get more recommendations as being a safer way to go.
Could be time for a rethink on the mixture then, as 1.4 continues to get more recommendations as being a safer way to go.
OP
Your assertion is ill-founded: the dive community already uses different mixes.
For example, North Florida cave divers commonly use 30 or 31%, because 32% is just a bit rich for many of the caves. North Carolina wreck divers commonly use 28%, so they can comfortably go to 130 ft to see some of the wrecks.
One BIG reason people "stick to the" 32% mix (which is often 31...) is because that is what the membrane system supplies. It is a big fuss to mix other than what the membrane gives you, and little to gain for it, so why make a fuss? 36% used to be a lot more popular, but the advantages are outweighed by the operational disadvantages. Back when all blends were done by hand using partial pressure methods, you did need to make a decision on the percentage, Now, however, few mixes are custom.blended, because most come from membrane systems that are set up for one mix only.
Bubblesong
Contributor
It seems to me that the mix should be adjusted to the desired dive depth, and calculated as part of the planning of the dive. Of course one plans in contingencies, not just optimal plan execution. This assumes that you aren’t buying “on tap” Nitrox, but can get exactly the mix you want for a particular dive.
I think that that would be correct if your goal was to max the bottom time. Most divers i know are single tank divers and are not going to get 40 min at 100+ ft because of an al80 being 77 cuft rock bottom numbers back on board psi and other factors. The idea of most divers trying to get the mix that will give them the most bottom time in this day is not common. If I use a 40% mix at say 85 ft because it fits a formula for ideal mix. If it gives me say a time of 50 min ndl and 53 min based on sac then the use of 40 is moot. especially if you are only making one dive or maybe 2. Makiing 5 dives a day is another story.
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