I can see a benefit of nitrox especially when the instructor has to make lots of up and down trips (ESA etc) but 60% seems like overkill and as was mentioned how many OWSI are qualified to dive 60%. I think 40% would do just fine.
Why not 60% O2 for prof during OW?
- Thread starter RonzoTheGreat
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John_B
Grasshopper
Why use a higher pct. of Nitrox than is needed? It would just run up the CNS O2 clock...
I agree with Jeff, it solves a non-existent problem.
I agree with Jeff, it solves a non-existent problem.
rmc77
Registered
I would like to say it depends... just to sound like I'm really into decompression theory. 
But I guess it's only a matter of cost like has been already said here.
With EAN60 you would have outrageous amounts of NDL. With air, off course you would have lower NDL limits. But there is another important factor too: gas consumption. Depending on your consumption rate, air NDL limits will be close to gas volume limits. So, what's the point of using such rich (and costly) mix if you'll end up with an empty tank (considering you're using a S80) way before reaching the NDL anyways?
And final but not last, please remember that OTU limits are not affected by S.I like CNS so... successive long dives (very common for dive professionals) on such high O2 exposure are to be taken for granted.
Rafael
But I guess it's only a matter of cost like has been already said here.With EAN60 you would have outrageous amounts of NDL. With air, off course you would have lower NDL limits. But there is another important factor too: gas consumption. Depending on your consumption rate, air NDL limits will be close to gas volume limits. So, what's the point of using such rich (and costly) mix if you'll end up with an empty tank (considering you're using a S80) way before reaching the NDL anyways?
And final but not last, please remember that OTU limits are not affected by S.I like CNS so... successive long dives (very common for dive professionals) on such high O2 exposure are to be taken for granted.
Rafael
OP
RonzoTheGreat
Contributor
OP
RonzoTheGreat
Contributor
also, its a just a conversation. i was completely aware of the costs and gear issues, just focusing on the bio side of it i guess ... especially since tables and consumption and such are THEORY as opposed to proven ... (hence various tables)
just a conversation.
just a conversation.
Something to consider is the total depth of the water, not just the depth of the students. Let's take a popular New Mexico instructional site, the Blue Hole. It has a maximum depth of 87 feet, with OW students working off platforms at much shallower depths. An instructor working a lot of classes might be tempted to use 60%. So the instructor is doing the tour portion of the dive, and suddenly a student has a buoyancy problem and starts to plummet. The instructor dutifully chases, and before long is below the MOD (maximum operating depth) for 60%. What follows might not be all that good.
Anti-Hero
Contributor
Huh?
Tables and consumption are theory? Tables are perhaps theory backed by a lot of empirical data but consumption calculations are pretty solid given a known SAC rate. However "proven" as in feeling better is anecdotal at the very best. I do *think* I feel better after diving a rich mixture, but there is little science to back it up. Is that a proven quality or is that a placebo effect since i think I'm going to feel better?
The other basics like exposures (as in breathing 60% O2) are far more relevant to this "conversation," especially the "bio side."
I guess I'm just not following what exactly you're asking, or why you picked 60%? Was it just some arbitrary mix for conversation?
Anti-Hero
Contributor
Perhaps, but oxygen toxicity isn't something that magically happens when you cross some arbitrary boundary like 1.4 / 1.6 PP02. There have been recorded exposures of well over 2.0 ATA without any negative side effects. But why any instructor would use 60%, even in theory or for conversation is beyond me.
Ronzo,
A friend and I sometimes to use mixes to 40% and sometimes a little higher. We mix our own deco bottles, and when the pressure gets too low in the O2 tank, we mix what we can for shallow dive backgas. When topping with 36 it is very easy to go over 40%. The only real benefit is a very low N2 load at the end of a couple dives.
A friend and I sometimes to use mixes to 40% and sometimes a little higher. We mix our own deco bottles, and when the pressure gets too low in the O2 tank, we mix what we can for shallow dive backgas. When topping with 36 it is very easy to go over 40%. The only real benefit is a very low N2 load at the end of a couple dives.
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