Air break on rebreather, how to proceed?

[tbone1004]

Gross!!! Making me rethink deco training coming up.

don't worry about it, like was said above, if you follow some of the general guidelines you shouldn't ever experience it.

Very good thread, thank you. But as I expected there is not one single truth.
I think I will start doing airbreaks on rebrether as well. But I'd like to stay on CCR so I will lower the pO2. And here is the next problem: which pO2 shall I use? An AIRbreak is done on air. In a CCR I will not go down to 21% of oxygen. Perhaps I will run it on 0.4 pO2 but is this an airbreake?

Air breaks aren't necessarily done on air. They're done on whatever you happen to be using for backgas or some leaner bottom/deco mix if you're on a really hypoxic mix. In cave country, our air breaks are almost exclusively done on EAN32 for example because we don't carry air with us. I'm actually pretty certain that there are no dives that I would expect to do where my "air break" would actually be done on air...

 

[Agro]

Air breaks or back gas breaks seem to be only advocated for when using 100% for extended periods IME

I can easily run 1.2 or 1.3 on deco instead of 1.6, which is impossible to keep anyway because of offgasing. So you think if I run 1.2 all the time, an airbreak does not make sense?

On my actual project I dive to 35/37m, stay there an work for about 60 min. Dil ist air. I make much more deco then what the dive computer sais because of rather heavy workload. My OC bailout is EAN34. Does it make sense to use this gas for OC airbreak? On 6m it gives me 0.54 pO2. Wouldn't it be better to run the rebreather at 0.4 bar? Dil flush and buoyancy is no problem at all.

I can easily run 0.4 on my liberty, this is the minimum setpoint, no red light. And I have no problem to control these 0.4 during 5 min airbreak.

 

[tbone1004]

I can easily run 1.2 or 1.3 on deco instead of 1.6, which is impossible to keep anyway because of offgasing. So you think if I run 1.2 all the time, an airbreak does not make sense?

On my actual project I dive to 35/37m, stay there an work for about 60 min. Dil ist air. I make much more deco then what the dive computer sais because of rather heavy workload. My OC bailout is EAN34. Does it make sense to use this gas for OC airbreak? On 6m it gives me 0.54 pO2. Wouldn't it be better to run the rebreather at 0.4 bar? Dil flush and buoyancy is no problem at all.

I can easily run 0.4 on my liberty, this is the minimum setpoint, no red light. And I have no problem to control these 0.4 during 5 min airbreak.

If you stay at 1.2/1.3 then I wouldn't bother about air breaks.
I would use EAN34 for air breaks in that case, but you can flush the breather if you want. Just uses a lot more O2 for the extra flushes.

 

[broncobowsher]

Remember a rebreather is little more than a continuous nitrox blender on your back. You can always vary the strength of the nitrox.

 

[Agro]

Great forum, great members, great information, thanks a lot. But still I am not sure if I shall make airbreaks (no matter how) or not.
Are there any recommendations by diving agencys?

 

[JonG1]

Hasn't the theory of "monitoring" offgassing via solenoid or CMF bypass activity been debunked?

I thought the accelerated drop in ppo2 early in deco was more likely attributable to pockets of gas laden with inert being displaced gradually into the loop from crevices that were hard to flush.

 

[rddvet]

Hasn't the theory of "monitoring" offgassing via solenoid or CMF bypass activity been debunked?

I thought the accelerated drop in ppo2 early in deco was more likely attributable to pockets of gas laden with inert being displaced gradually into the loop from crevices that were hard to flush.

I was taught that you’re expelling offgassed gas into the loop which leads to a drop in p02 and an increase in gas volume. When I dive trimix vs nitrox it’s very obvious. You can really experience the speed at which you’re off gassing helium.

 

[JonG1]

Pretty sure the volume of gas is insufficient to alter the loop composition, but I may be wrong.

I've seen some figures on it somewhere from someone cleverer than me!

 

[wedivebc]

Nope. I follow the rule for OC. There is no rule for CCR

There has been no serious study on recreational CCR regarding air breaks because I think the value of air breaks on OC are anecdotal at best.

 

[rddvet]

Pretty sure the volume of gas is insufficient to alter the loop composition, but I may be wrong.

I've seen some figures on it somewhere from someone cleverer than me!

I was told the opposite by two instructors. I was thrown off that early in deco on helium it was harder to keep my p02 up and was told it was due to offgassing. Specifically helium coming out quickly. I also discussed with an instructor that you can see when offgasing slows as deco progresses. I’m fairly new to rebreathers so someone else can comment and tell me if I’m wrong or not. Possible I misunderstood my instructors’ points but I dont think so.