[QUOTE=hoopa]i think the answer this guy is looking for is in the partial pressure % of a dive. As you know-- when you go deeper your o2% doubles each ata-- so at the surface you have 21%o2-- at 150ft your at 5.5 ata-- so your po2 at that point will be 1.15 or 5.5X the .21 of o2 you had at the surface--- so you now have 5.5times the molecules of o2/co2 ect in each breath-- so at that point your scrubber is having to remove 5.5times more co2 then it does at the surface.. hence faster use of the scrub.. Where this point will stop is the fact that your rebreather will have a 02 meter-- and lets say you have it set for 1.2 --- so at about 5.7 ata(188ft) your rb will adjust the amount of o2 in the system to keep your unit at 1.2 p02--- so at that point you have hit the point of diminish and return(your going deeper yet your not scrubbing more c02 cause there is less in the system to start with at each breath)

The Amount Of O2 used and CO2 produced not dependent of depth. The only factor is work load. That is the whole reason why CCR's are more effiecient relative to OC the deeper you go.

Stuart's particle density/occlusion explanation is the true reason for decreased scrubber efficiency at depth. The bottom line is 'DWELL TIME'. The more time CO2 is in contact with the Scrubber binding sites the more of it will be removed. The gases are pushed through the loop at a fairly constant rate, assuming a steady breathing cycle from the diver. Therefore as the increase in inert gas density means more moelecules of gas blocking the available binding sites, the CO2 which is always moving at the same speed through bed, will have less time in contact with the scrubber, and therefore less of it will be removed.

I beleive IANTD had a recommendation for turn times based on depth of the dive, to give you a guideline to work from.

The deeper you go the slower and eeper your resperation should be, without skipping of course.

There has been a lot of chat about the ineffeciencies of absorbents at depth recently, especially following the death of Dave Shaw in South Africa, on a deep (900ft) body recovery.

This has prompted some speculation as to the possibilty of employing 'active' circulation in the loop. The idea of more elctronics/electrics is a little fightening, and perhaps not terribly relevant in shallower dives, but for extereme depths and commercial work with a lot more surface support it may hold promise.

Speaking to a Sat. Supervisor freind of mine he said the divers are essntially working on very long rebreather, with the scrubber and gas introduction being done ate the surface and an active system both delivering and recovering gas from the diver at depth. I beleive that they would also carry a Bailot rebreather system, to get tghem back to their habitat.

Cheers