re breathers + deco stops?

[Vin]

What effects do rebreathers have on nitrogen in the blood stream after extended periods? Do they function under diffrent tables? I assume they must but don't realy know. I was watching an Imax film on Cocos, they were down @ 130 feet for hrs..... sounds like 1 hec of a deco stop. But what are the facts?

thanks,

Vin

 

[Genesis]

What effects do rebreathers have on nitrogen in the blood stream after extended periods? Do they function under diffrent tables? I assume they must but don't realy know. I was watching an Imax film on Cocos, they were down @ 130 feet for hrs..... sounds like 1 hec of a deco stop. But what are the facts?

thanks,

Vin

A closed-circuit rebreather shortens most deco schedules, since they minimize the percentage of inert gas in the mix at all times (e.g. your mix is ALWAYS optimum) as they are able to control the PO2 within reasonably tight limits.

For most dives this results in greatly reduced decompression requirements.

For a "regular" OC deco schedule you might have a PO2 of 1.6 at your gas switch, but as soon as you start ascending the PO2 goes down - which is undesirable. A rebreather avoids this as it can enrich the O2 content as you ascend, maintaining the setpoint you specified. As such you offgas more efficiently.

Of course the potential problem with this is that a rebreather CAN fail; for that reason you need access to enough gas to be able to complete decompression on open circuit scuba if it does, otherwise you're in BIG trouble if it does.

 

[Drew Sailbum]

Rebreather divers do incurr deco obligations just like open circuit divers. However with the ability to maintain a higher PPO2 (and thus lower PPN2), CCR divers often have much shorter deco schedules.

During the ascent, computer controls on CCR units can help maintain a blend that promotes offgassing of accumulated nitrogen more efficiently. That can be accomplished over exceeding long times in stepwise fashion making much of the dive one long ascent.

It might seem that rebreather divers have seemingly unlimited bottom time, but there are limits afforded by the equipment - just not necessarily the amount of gas carried. Scrubber chemicals have a limited life and RB divers learn that pushing the limits is foolhardy.