Do you rebreather guys use high PPO2's for deco as well?

[Jimmer]

I've been fascinated by rebreathers for at least a good 10 years now, and in doing my research it seems that PPO2 of 1.2 is common for the bottom time portion of the dive. But I was curious if you guys ever run higher PPO2's, 1.6 for example, during deco, like OC divers might.

Jim

 

[DepthCharge]

I've been fascinated by rebreathers for at least a good 10 years now, and in doing my research it seems that PPO2 of 1.2 is common for the bottom time portion of the dive. But I was curious if you guys ever run higher PPO2's, 1.6 for example, during deco, like OC divers might.

Jim

On deco I can usually maintain > 1.45. For various reasons it's pretty much impossible to maintain a 1.6, unless you do alot of O2 flushes

 

[Jimmer]

Ok, so 1.6 is hard to maintain, but the point is you do go to elevated PPO2's for deco then?

 

[wedivebc]

Depending on deco time and what my CNS exposure has been during the dive but I generally maintain my 1.3 setpoint then perform one or several O2 flushes during deco. I do not use the higher PO2 to accelerate the deco more as a safety factor.

One reason 1.6 is hard to maintain is your body is releasing inert gas into the loop as you deco

 

[Jimmer]

Depending on deco time and what my CNS exposure has been during the dive but I generally maintain my 1.3 setpoint then perform one or several O2 flushes during deco. I do not use the higher PO2 to accelerate the deco more as a safety factor.

Ok, I figured the CNS clock must come into play considering the length of dive time you guys can get with a rebreather.

 

[Mr.X]

Ok, I figured the CNS clock must come into play considering the length of dive time you guys can get with a rebreather.

CNS comes into play for any longish dives. Some dives I conducted in Canada at depths exceeding rec. limits (200++) required higher deco. setpoint (flushing) and then a quick chamber ride where elevated PO2 could be maintained comfortably. This was commercial work. Having my deco. obligations maintained by a chamber tech. in a comfortable setting beats sitting at the 20-15' stop for a what seems like forever while flushing and watching RB displays. Of course, we were trying to maintain 1.6 as best as possible. 1.5 was doable.

X

 

[DiveTub]

Of course the other option is surface supplied O2 at 6m and up.

This is common on many of the more technical dive boats. Where you will get off your loop when you get to the Deco Bars and go onto O2. Gives you much much cleaner Deco, of course still keeping a watchful eye on your CNS loading.

Cheers
Chris

 

[Gill Envy]

I don't do long deco diving but the bottom line is the same; constant po2 diving optimizes exposure continuously. because as you ascend o2 must be added to maintain constant po2 the mix is already getting richer and richer compared to variable po2 nitrox OC and you are already getting most of the advantages of high po2. the difference between 1.2 and 1.4 in the world of constant po2 is peanuts in terms of off gassing, but I do do it anyway some times just for a safety margine. I'm usually back into the NDL range long before I begin wrapping up the dive and doing a safety stop.
g

I've been fascinated by rebreathers for at least a good 10 years now, and in doing my research it seems that PPO2 of 1.2 is common for the bottom time portion of the dive. But I was curious if you guys ever run higher PPO2's, 1.6 for example, during deco, like OC divers might.

Jim

 

[Jimmer]

Of course the other option is surface supplied O2 at 6m and up.

This is common on many of the more technical dive boats. Where you will get off your loop when you get to the Deco Bars and go onto O2. Gives you much much cleaner Deco, of course still keeping a watchful eye on your CNS loading.

I assumed some of you probably used OC O2 for deco as well. Very interesting info, thanks everyone. I've been fascinated by rebreathers for probably the past 10 years, and I actually have a file folder full of drawings and designs I sketched out when I was in high school. I'm planning on going to CCR at some point in the future.