Rebreather Discussion from Brockville Incident

[Larry7895]

Hi Gian,

Certainly not. I would not rule it out.

Simon M

---------- Post added July 19th, 2013 at 06:55 AM ----------



Hello Larry,

OK, I understand your question. Certainly possible on both. As to which is more likely... this probably does fall into the category of not possible to answer in a definitive sense. Moreover, merely specifying OC or CC is probably too coarse a definition of the circumstances to be useful. There is considerable variability in the breathing characteristics among both types of device depending on user mods and maintenance. How much exercise is being performed also plays a big role. If I was forced to choose I would say it is probably more likely on CC, but not to an extent that would influence my choice between CC and OC in any way. Again, hope this makes sense.

Simon M

Thanks Simon. Makes sense. I also re-read a few of the papers you sent and I think I also understand it as well which is a bonus. Many thanks once again. Larry

 

[gianaameri]

Survived yet another day of russian roulette Happy horse beating.

During WWII, the soldiers were going through 3 distinct phases:

Phase 1: "It can't happen to me."
Phase 2: "It can happen to me, and I'd better be more careful."
Phase 3: "It is going to happen to me, and only my not being there is going to prevent it."

You appear to be a Phase 1 rebreather diver.

Rebreather diving is dangerous and the better approach to manage the risks is to identify them and mitigate them.

The best research from the USN is telling us that the max WOB on rebreather should be:

a. 2.15 j/l for air dives to 40 meters
b. 1.93 j/l for Trimix dives to 100 meters

So, to mitigate the risk of CO2 Retention, you want to buy a unit with a WOB which is within these limits.

There is also Elastance and Hydrostatic Imbalance to consider in addition to WOB.

From your Avatar, you dive a rEVO.

There are different versions of your rebreather released over the years. Some of the earlier ones it is reported had a not so good WOB relative to the more recent ones. This is not uncommon with rebreathers. Some rebreathers in their earlier versions had WOB well in excess of the USN permissible upper limit.

Check your unit is one of the more recent ones and ask the manufacturer for the WOB, Elastance, and Hydrostatic Imbalance numbers and then check them against the USN upper limits (if you want to mitigate risk).

Don't buy/dive a unit outside the USN limits to mitigate CO2 Retention risk and upgrade your unit if it is one of the earlier versions with excessive WOB.

That is a first step to risk mitigation which with a "it is not going happen to me" attitude to risk management you may miss.

Then there is a problem of how the unit is being worn by the diver and dived.

Especially with back-mounted counterlung rebreathers like yours, if the unit lifts from your back even a small amount, then this will increase your WOB and Hydrostatic Imbalance beyond the laboratory test WOB limit. Then dive it hard in a current, same as you are used to dive OC (old habits die hard), and risk increases even more.

So, you can help your luck with a bit of information gathering and risk management, but if you do not know and measure the risks in the first place, then you cannot mitigate them.

 

[mathauck0814]

During WWII, the soldiers were going through 3 distinct phases:

Phase 1: "It can't happen to me."
Phase 2: "It can happen to me, and I'd better be more careful."
Phase 3: "It is going to happen to me, and only my not being there is going to prevent it."

This - of course - would be relevant if I were a WWII soldier. As it is, I am not.

Rebreather diving is dangerous and the better approach to manage the risks is to identify them and mitigate them.

Rebreather diving has risks which can be managed. I flatly reject your designation of "dangerous". Though if you feel it to be too dangerous, I'd suggest not participating.

From your Avatar, you dive a rEVO.

Correct.

There are different versions of your rebreather released over the years.

I love history too.

Check your unit is one of the more recent ones and ask the manufacturer for the WOB, Elastance, and Hydrostatic Imbalance numbers and then check them against the USN upper limits (if you want to mitigate risk).

Unit is the most current - as with anything, improvements should continue to be made. When they are, you continue to buy the new technology. Anyone who believes that you buy one rebreather for life is probably unqualified to dive one. You buy the best (in your opinion and for your needs) and upgrade when necessary and/or prudent.

Don't buy/dive a unit outside the USN limits to mitigate CO2 Retention risk and upgrade your unit if it is one of the earlier versions with excessive WOB.

This PSA Brought to you by the fine people at Gianaameri

That is a first step to risk mitigation which with a "it is not going happen to me" attitude to risk management you may miss.

Dive the unit correctly and it won't happen to you either.

 

[gianaameri]

Dive the unit correctly and it won't happen to you either.

That is true if the unit has a low WOB and a low Probability of Failure.

It is not true if the unit has a high WOB and a high Probability of Failure.

It is a numbers game, not a skill game.

People far better than you think you are are dead already.

 

[Doppler]

Simon: can you point me towards any information you have that helps to qualify the statement that high CO2 worsens narcosis, and predisposes to cerebral oxygen toxicity? Thanks, mate. Hope all is well.

 

[Superlyte27]

All this WOB conversation is interesting. I remember thinking about it yesterday during my 3:20hr dive in a high flow cave.

I remember thinking how effortless the dive was even at depth and in high flow. Swimming or scootering each breath took as much effort as each breath I take now sitting at this laptop. And then came the 2hr ride home. My wife who was tagging along with me yesterday asked if she needed to drive home. It was nearly 11pm after a long day of diving, but the effort spent diving a rebreather with a perfect mix of gas (combined with the 60 minute scooter ride) was minimal. I've found that even after very long days of diving, you have more energy on CCR than you do on OC at the end of the day, and this time was no different. Add in the fact that I did a 30 minutes less deco than my OC buddy on this dive, and I carried 70lbs instead of 140lbs to the car, and it's a no brainer for me.

Rebreathers can kill the lazy, ignorant or complacent
Rebreathers can change your diving for the better in ways you couldn't possibly imagine.
Don't believe ANY of the hype... dive one for yourself and see.

 

[HIGHwing]

This - of course - would be relevant if I were a WWII soldier. As it is, I am not.

That's funny right there.

 

[Superlyte27]

Yah, I chuckled when I read it.

 

[gianaameri]

All this WOB conversation is interesting. I remember thinking about it yesterday during my 3:20hr dive in a high flow cave.

I remember thinking how effortless the dive was even at depth and in high flow. Swimming or scootering each breath took as much effort as each breath I take now sitting at this laptop. And then came the 2hr ride home. My wife who was tagging along with me yesterday asked if she needed to drive home. It was nearly 11pm after a long day of diving, but the effort spent diving a rebreather with a perfect mix of gas (combined with the 60 minute scooter ride) was minimal. I've found that even after very long days of diving, you have more energy on CCR than you do on OC at the end of the day, and this time was no different. Add in the fact that I did a 30 minutes less deco than my OC buddy on this dive, and I carried 70lbs instead of 140lbs to the car, and it's a no brainer for me.

Rebreathers can kill the lazy, ignorant or complacent
Rebreathers can change your diving for the better in ways you couldn't possibly imagine.
Don't believe ANY of the hype... dive one for yourself and see.

You probably felt so good because your brain released those neurotransmitters that we cave addicts seek and drive us further into the cave and deeper penetrations to trigger the same sensation or better.

Add to those neurotransmitters a bit of CO2 and N narcosis and it is the perfect natural high.

It has little to do with rebreather WOB. If rebreather WOB could be measured as you describe it NEDU and QinetiQ would rely on the personal recounts of people like yourself, rather than sophisticated machinery and equipment as they instead use to measure WOB.

However, you could make a good ad for rebreathers with your recount...

Sounds like you had a good cave dive.

 

[Dr Simon Mitchell]

Simon: can you point me towards any information you have that helps to qualify the statement that high CO2 worsens narcosis, and predisposes to cerebral oxygen toxicity? Thanks, mate. Hope all is well.

Hello Steve,

pm sent.

Simon