DevonDiver
N/A
Having written a reply to the 'What role does OxTox play in recreational diving?' thread (which has just been closed?), I thought I would transfer it here for discussion, as it raises some valid points..
Technically, you do hit the nail on the head with this. However, it is important to remember why the MoD limits were introduced and, then, subsequently made progessively more and more shallower as more diving statistics became available over the decades.
MoD is calculated as the depth at which a given breathing gas reaches 1.4PPO2. When a diver exceeds that MoD (or more importantly, that PPO2) their STATISTICAL likelihood begins to increase dramatically.
It is not a case that you "WILL" convulse at 1.4 or 1.6 PPO2.... it is a case that you COULD convulse under those circumstances.
The diving community has agreed, by consensus, that divers ideally should not exceed the statistical likelihood of OXTOX that exists beyond PPO2 of 1.4. The line has to be drawn somewhere and, after decades of diving, THAT is where the line was drawn.
It may be simplistic to define OXTOX prevention in terms of adherance to max PPO2/MoD, rather than focusing on the CNS Clock, but it is also a very effective approach that goes a long way to increasing diver safety AND developing an attitude of conservatism in dive planning/conduct.
It is also important to remember that the onset of OXTOX is also heavily influenced by numerous (and mostly not yet understood) physiological and physical factors that differ with every diver and every dive. In that respect, a conservative approach to limiting PPO2/MoD as a 'baseline' to OXTOX avoidance seems, IMHO, to be wise.
I disagree that the issuance of strict MOD/PPO2 limits is about easing the burden of the dive educator... especially as we 'should' be teaching students about CNS toxicity anyway.
MODs and PPO2 limits are about saying to students "This is the line that will keep you safe. Overstep that line and things could go fatally wrong for you."
Technically, you do hit the nail on the head with this. However, it is important to remember why the MoD limits were introduced and, then, subsequently made progessively more and more shallower as more diving statistics became available over the decades.
MoD is calculated as the depth at which a given breathing gas reaches 1.4PPO2. When a diver exceeds that MoD (or more importantly, that PPO2) their STATISTICAL likelihood begins to increase dramatically.
It is not a case that you "WILL" convulse at 1.4 or 1.6 PPO2.... it is a case that you COULD convulse under those circumstances.
The diving community has agreed, by consensus, that divers ideally should not exceed the statistical likelihood of OXTOX that exists beyond PPO2 of 1.4. The line has to be drawn somewhere and, after decades of diving, THAT is where the line was drawn.
It may be simplistic to define OXTOX prevention in terms of adherance to max PPO2/MoD, rather than focusing on the CNS Clock, but it is also a very effective approach that goes a long way to increasing diver safety AND developing an attitude of conservatism in dive planning/conduct.
It is also important to remember that the onset of OXTOX is also heavily influenced by numerous (and mostly not yet understood) physiological and physical factors that differ with every diver and every dive. In that respect, a conservative approach to limiting PPO2/MoD as a 'baseline' to OXTOX avoidance seems, IMHO, to be wise.
1)It's just EASIER to teach, "don't exceed 1.6 PPO2" EVER or you will die, than it is to explain that you can use the oxygen clock and provide the information of that to plan dives within the window of acceptability.
I disagree that the issuance of strict MOD/PPO2 limits is about easing the burden of the dive educator... especially as we 'should' be teaching students about CNS toxicity anyway.
MODs and PPO2 limits are about saying to students "This is the line that will keep you safe. Overstep that line and things could go fatally wrong for you."
With respect to recreational diving......
