Deep water rebreathers?

[pt40fathoms]

I have heard and read about people who regularly dive to depths of 300 to 700 feet with a rebreather. The claim being that the unit continually adjusts the amount of O2, making the dive longer at depth and the deco stops fewer and shorter.

Have they got water on the brain, or is their some validity to the claim, and IF so, what make and model of rebreather is designed for this type of diveing???

 

[roakey]

Unlike OC or SCR diving where the % of O2 in the mix is constant, CCRs adjust the % of O2 in the loop.

Nitrox gives you longer bottom times because there's less Nitrogen in the gas than normal air. What a CCR can do (I'm simplifying) is adjust the % of O2 in the loop in order to minimize the amount of N2 in the loop. In other words, the O2 is maximized just below PPO2 toxicity limits to minimize N2 uptake.

So their “tables” are different than ours, since the “normal” tables assume a fixed % of O2 and theirs are varying throughout the dive.

A terse way of saying it is that OC and SCRs have a variable PPO2 throughout the dive and CCRs [can] have a fixed PPO2 throughout the dive.

Roak

 

[Hanz]

I wouldn't say that people regularly dive that deep,however, closed circuit rebreathers have been used even deeper. They have also been used for manyhours on a single fill, but are usually used at 200' or less. a rebreather functions by reusing the breathed gas after "cleaning" the gas of waste carbon dioxide via chemical process and re-intruducing oxygen into the gas via a bottle carried with the rebreather. Closed circuit rebreathers also control the oxygen partial pressure in the breathing gas as well controling the other elements of the breathing mix. (another mix bottle of nitrox,helox or trimix is also carried) so even at depth:
1. the OPP is held to within safe levels so no oxggen toxicity.
2. Trimix or helox mix control the narcosis problem.
3.Since the oxygen mixing is based on partial pressure and not percentage,so for example you could have the mix you are breathing contain a much larger percentage of oxygen than say air(21%) but the partial pressure of the oxygen is controled at a low level, therefore, less nitrogen or helium is used, and therefore longer dives without deco are possible and even when deco is required the stops are shorter.

 

[pt40fathoms]

So a CCR unit constantly adjust the PPO2 to keep you within a non toxic level. Does that mean that all CCR units can be dived to the deeper depths for a longer time. Or is it limited to a few makes and model. Secondly, what gas would be used to dilute the breathing gas mixture, so as to not load you up with nitrogen?

 

[Hanz]

CCRs used for depths greater than 300' are custom made to fit the aplication. The diultent gas would be helox (helium/oxegen) or
Trimix (helium/nitrogen/oxygen) for deep dives. Mixed gas CCRs are not to be confused with 100% oxygen rebreathers which have extreme depth limitations and are mainly used for undetected approach by SEALS and the like.

 

[pt40fathoms]

OK, so the claim is valid, and it is possible to dive to depths of 700 feet plus. Now for the who? Who makes rebreathers that perform under those conditions?

 

[Hanz]

Mostly science types use deep CCRs to film and study animals that only live that deep. As for who makes them, I don't know. You would have to check with typical rebreather manufacturers like Draeger, Innerspace, etc...

 

[padiscubapro]

Originally posted by pt40fathoms
OK, so the claim is valid, and it is possible to dive to depths of 700 feet plus. Now for the who? Who makes rebreathers that perform under those conditions?

The Infinito has been testeed to over 250 meters (approx 820 fsw)

The inspiration is rated for 100m but I know people who have gone to over 150M on the unit

The megladon is rated for 500 fsw

CCR 2000 - rated at 1100 fsw/ 330 msw

Just a sampling

 

[Reg]

New to the list and just read this thread but here in Grand Cayman we use the Inspiraiton rebreathers for regular diving between 200 and 350 FSW combined with VR3s for tables.

Although they used to be used for scientific and military use exclusivly there are people all around the world diving them for recreational purposes now.

Here in cayman we have had 75 CCR visitors in the last 12 months alone each staying for a week or more.

They really are quite amazing.