Oxygen narcotic?

[cerich]

And the fourth gas is...? H2?

Not that I'm ever gonna take that specialty, it's purely intellectual (AKA geeky) curiosity.

hydrogen, helium, nitrogen and oxygen

 

[VE7DAC]

Thanks for the explanations, everyone, there's too much good info here for me to reply to everything.

If I'm understanding this right, O2 being narcotic isn't an issue on its own, because the CNS limit gets in the way before you can have enough partial pressure to notice. But it can add to nitrogen narcosis, which obviously can be safely experienced. That also explains why deco/rebreather divers don't worry about it, since the 1.4-1.6 PPO2 on its own is negligibly narcotic.

 

[cerich]

Thanks for the explanations, everyone, there's too much good info here for me to reply to everything.

If I'm understanding this right, O2 being narcotic isn't an issue on its own, because the CNS limit gets in the way before you can have enough partial pressure to notice. But it can add to nitrogen narcosis, which obviously can be safely experienced. That also explains why deco/rebreather divers don't worry about it, since the 1.4-1.6 PPO2 on its own is negligibly narcotic.

yeah but you need to stop thinking ccr and 1.4-1.6, really..that is deco and could apply OC or CCR. It really isn't a good idea to run that high CCR

 

[helodriver87]

Thanks for the explanations, everyone, there's too much good info here for me to reply to everything.

If I'm understanding this right, O2 being narcotic isn't an issue on its own, because the CNS limit gets in the way before you can have enough partial pressure to notice. But it can add to nitrogen narcosis, which obviously can be safely experienced. That also explains why deco/rebreather divers don't worry about it, since the 1.4-1.6 PPO2 on its own is negligibly narcotic.

That's a decent summary. Oxygen is treated as equally narcotic because, while it should theoretically be more narcotic, by metabolizing some of it, the potential is lowered. So we call them equal. That may be a bit conservative, but not restrictively so. Since most deco is done shallower than 100' (the typical END of most bottom gasses), it's not an issue. It's only when you get into deeper stuff like 120 and 190 deco gasses that you need to account for narcotic potential in your mix.

 

[VE7DAC]

yeah but you need to stop thinking ccr and 1.4-1.6, really..that is deco and could apply OC or CCR. It really isn't a good idea to run that high CCR

Fair enough, I'm nowhere near diving a rebreather. Just working on AN/DP, and those are the numbers they use for working phase and deco phase.

 

[NAM001]

IMO ,,,,, I would say that all gasses have some sort of narcotic effect. However the effect is probably some what moot at low PP's. what is that low pp I think it depends on the gas. The downside to O2 is perhaps not in the rec depths and thus using nitrox is an alternative as if the N2 is the primary narcotic driver at those depths. the deeper you go the more O2 becomes a player and hence in trimix you are now using END as opposed to EAD. Again IMO if you went deep enough probably helium would become a problem. that may be 2000 ft though making its effects moot for normal tech diving in a few hundred ft. Also our intended current use of nitrox may not have anything to do with gasses being narcotic rather than being a controllable gas for NDL / deco matters. If you look at 6 atm with 80% N2 you are looking at a PPN2 of what 4.8 and you are narced. If narced is a symptom of the narcotic effect of N2 then is shows at what PPN2 is not safe to be exposed to. It can also in my untrained mind be true that before you have a narcotic issue with O2 you will hit O2 toxisity roblems. . Below that PPo2 by its self is not a problem but in conjunction with the narcotic effects of N2 it may be additive and with in the rec depths is not a threat as the sum of both PP's are not high enough to be a problem. I wish I knew more about the combined effects worked. This is the only logical view I can have that will allow O2 not to be considered as a threat in the rec depths. My thoughts also tend to support the idea of using END to keep the combined effects in the rec world no matter what depth you are at.

 

[helodriver87]

Don't think of it in terms of just PO2, think of it in terms of P(Narcotic Gasses), or PO2+N2. From a narcosis standpoint, it doesn't matter what the proportions of O2 and N2 are. They're equally narcotic. Breathing O2 at 80', in theory, should have the same narcotic potential as air (it obviously has other, separate issues).

If I want to keep my END at 100 or less, the maximum PO2+N2 I can have is 4.0. If I'm shallower than 100, problem solved. Just watch the PO2. If I'm deeper, just subtract that 4.0 from ambient pressure and convert the remaining balance to FHe.

 

[cerich]

Fair enough, I'm nowhere near diving a rebreather. Just working on AN/DP, and those are the numbers they use for working phase and deco phase.

1.4 max working phase is light work, if you find yourself working hard back it off (go shallower if possible on OC mix), but generally run times in OC are not gonna push the time needed that ox clock is a big concern (still track OTU) , on CCR running a 1.4 especially on long dives with a series of them planned is problematic and lots have tried and woken up with "burnt" lungs a few days in.. YMMV, go keto and stay hydrated if you wanna push that margin that tight

 

[VE7DAC]

1.4 max working phase is light work, if you find yourself working hard back it off (go shallower if possible on OC mix), but generally run times in OC are not gonna push the time needed that ox clock is a big concern (still track OTU) , on CCR running a 1.4 especially on long dives with a series of them planned is problematic and lots have tried and woken up with "burnt" lungs a few days in.. YMMV, go keto and stay hydrated if you wanna push that margin that tight

That makes sense. I've only met one rebreather diver locally, and he was running a pretty high setpoint (1.3), but he was also matching the ~1h dive times of the OC divers. Around here, the cold tends to be the limiting factor, there doesn't seem to be much of what you'd call long dives.

 

[VE7DAC]

Again IMO if you went deep enough probably helium would become a problem.

HPNS was an issue for Sealab, and I believe I've heard about it as a consideration for saturation divers. It can definitely be a problem.