Air break on rebreather, how to proceed?

[broncobowsher]

One does not build up a tolerance to narcosis.

I have known some drunks that passed as clean. Right up until they blew for the officer. The officer was rather amazed and commented that they needed help if they drank so often that they could convince the officer they were not drunk while triple the legal limit. So there is a tolerance to narcotic effects. Not 100%, but it does exist. Also ask those who took narcotic pain medication, acclimated to it and had to take a higher dosage. Repeat until a total addict.

The bad part in our world, not predictable. Does not follow the rules perfectly.

 

[rddvet]

I have known some drunks that passed as clean. Right up until they blew for the officer. The officer was rather amazed and commented that they needed help if they drank so often that they could convince the officer they were not drunk while triple the legal limit. So there is a tolerance to narcotic effects. Not 100%, but it does exist. Also ask those who took narcotic pain medication, acclimated to it and had to take a higher dosage. Repeat until a total addict.

The bad part in our world, not predictable. Does not follow the rules perfectly.

Not trying to be rude, but there is no way you can compare the narcotic effects of drugs and alcohol to the narcotic effects of nitrogen. They all work in very different ways on different and some common receptors in the brain. You're comparing oranges and hand grenades. There is no direct correlation or assumption that can be made. They may all cause you to do stupid things, but that doesn't mean if you build a tolerance to crack and need to use more, you'll also build a tolerance to nitrogen.

At the same time, I don't know where I sit on the debate. For years I felt as though I built a tolerance against repreated narcosis at the same depth. Now I really question if I did.

 

[rddvet]

@rddvet when you switch over to OC, learn to blow your nose without removing your mask. You can flip the nose pocket up and out of the way so you can blow your nose out easily on your way up.

I tried it once but it was after I had already gotten my sinuses pretty clogged and it didn't go super well. I may need to retry but earlier in the stuffiness.

 

[Superlyte27]

I think air breaks are foolish in CCR. Hbot, Long deco in OC ok, but that does not equal it being good for CCR.

personally I just run my dive at 1.2 or lower if it is going to be longer than 4-5 hours. Except in the frigid GL where I’ll run it at 1.3 - but I’m not in the water for more than 90 minutes then.

My reason for 1.2 has less to do with the risk of OT - the reason to do an air break and more to do with myopia. My eyes get messed for a couple of weeks after more than a week of diving daily if I push the SP up to 1.3 for more than about 3-4 hours a day.

The risk of OT is not linear but exponential- the greater the O2 the greater the risk therefore I don’t really see a good reason to keep flushing with O2 and then letting it drift down. Except to check that the cells are linear up to 1.6 - but you only need to do that once a dive beginning or end you choose.

I am reassured that at 1.2 I have 4 hours per day diving as per the NOAA tables. Which might not mean much.

The one thing I think we should remind people is O2 is not like narcosis where you can build up a tolerance. O2 is unpredictable both hypoxia and hyperoxia- one day no issues the next - not so good. I recall a study which I read in med school (years ago) where the British HB doc put recruits in his 2atm chamber and just waited to see when they toxed. Average was 20minutes. Longest was - he didn’t tox after 8!! Hours he went home, shortest was 8 minutes.
The other issue is you can’t stop OT once the cascade is in motion, you just have to ride it out - which in the water may not be survivable.

wish I was diving - supposed to be on the Big O this week.

That study is total BS. I've put literally hundreds of people in a chamber to 60' on pure o2 and not one (NOT ONE!!!) toxed. The school I was at had been doing about 30 people a month for DECADES and they couldn't remember the last time someone had toxed, if ever.

 

[Superlyte27]

I think air breaks are foolish in CCR. Hbot, Long deco in OC ok, but that does not equal it being good for CCR.

personally I just run my dive at 1.2 or lower if it is going to be longer than 4-5 hours. Except in the frigid GL where I’ll run it at 1.3 - but I’m not in the water for more than 90 minutes then.

My reason for 1.2 has less to do with the risk of OT - the reason to do an air break and more to do with myopia. My eyes get messed for a couple of weeks after more than a week of diving daily if I push the SP up to 1.3 for more than about 3-4 hours a day.

The risk of OT is not linear but exponential- the greater the O2 the greater the risk therefore I don’t really see a good reason to keep flushing with O2 and then letting it drift down. Except to check that the cells are linear up to 1.6 - but you only need to do that once a dive beginning or end you choose.

I am reassured that at 1.2 I have 4 hours per day diving as per the NOAA tables. Which might not mean much.

The one thing I think we should remind people is O2 is not like narcosis where you can build up a tolerance. O2 is unpredictable both hypoxia and hyperoxia- one day no issues the next - not so good. I recall a study which I read in med school (years ago) where the British HB doc put recruits in his 2atm chamber and just waited to see when they toxed. Average was 20minutes. Longest was - he didn’t tox after 8!! Hours he went home, shortest was 8 minutes.
The other issue is you can’t stop OT once the cascade is in motion, you just have to ride it out - which in the water may not be survivable.

wish I was diving - supposed to be on the Big O this week.

There's so much wrong with this post. You can't build a tolerance to narcosis. When this was studied, people could get through a single issue, but multitasking suffered no matter what. Some are more susceptible than others, but you're not getting better at mitigating the narcosis when multiple issues arise.

Also, once you start toxing, resolution is SIMPLE, provided you're not convulsing. Simply ascend or get off the rich gas. Call Paul Heinerth and ask him about the time he started toxxing at near 3.0 at depth in CCR and self rescued.

 

[tbone1004]

@Superlyte27 there is a difference in tolerance for oxygen when submersed vs. dry though. No one really understands why, but the chambers will confirm that people tox much sooner when in the water than they do if sitting in a dry chamber.

 

[Superlyte27]

@Superlyte27 there is a difference in tolerance for oxygen when submersed vs. dry though. No one really understands why, but the chambers will confirm that people tox much sooner when in the water than they do if sitting in a dry chamber.

His study said they were "in a chamber".

I'm aware of the differences. More than most. I was a chamber operator for more than a decade.

 

[tbone1004]

His study said they were "in a chamber".

I'm aware of the differences. More than most. I was a chamber operator for more than a decade.

I know, was clarifying for anyone that wasn't aware

 

[Superlyte27]

@Superlyte27 there is a difference in tolerance for oxygen when submersed vs. dry though. No one really understands why, but the chambers will confirm that people tox much sooner when in the water than they do if sitting in a dry chamber.

We know why, lol.
You're not working in a chamber. Your sac rate is probably .25. You're expending zero energy, except during vent, you're nice and toasty warm and hydrated.

Otherwise, you're likely swimming, shoveling, pressure washing, cutting/burning, etc, etc etc. All of them causing at best just a slightly elevated heart rate.

 

[Superlyte27]

@Akimbo when they did the tests at high ppO2 in the chamber while riding stationary bicycles, were they toxing like working underwater?