Will OC records always be deeper?

Abbo

There is a well-worn argument that says that though rebreathers are clearly more dangerous than OC in shallow waters, they are safer at trimix depths - and yet they tend not to be used in depth record attempts. What range of depths is the sweet spot where CC is safer than OC?

The deepest dive on OC is 330m: the deepest on CC is 270m. Dave Shaw's write up of his October 2004 dive to 270m in Boesmansgat in South Africa..
http://www.deepcave.com/images/Boesm...h_Oct_2004.pdf
..describes almost leisurely line-laying and exploration at this extreme depth. Nevertheless, clearly WOB and scrubber duration were problems, and seem likely causes of his tragic death in a working dive at the same depth early the following year. Though large radial scrubbers should overcome some of the duration problems, the significantly higher WOB of RBs seems pretty hard to engineer out. Beyond a certain depth I would have thought the higher WOB represents a serious hypercapnia risk on CC. Will we ever see rebreather divers setting depth records, or are they really inferior tools at extreme depth? -If so, at what kind of depth do you think OC starts to win out again over CC for safety?

Dutchy

Higher wob can easily be engineered out. Ventilation assisting exists but would you want to add another fallable part?

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Mark Chase

Deepest CCR dive is i believe 560m by Comex on Heleox but it didn't count because they were saturation divers returning to a habitat/bell.

Its was done on a CCR1000/Mk15.5 type unit I believe but id need to look back on my old notes to be sure.

I assume the main problem would be the electronics of the CCR imploding at depth. There may be some issue with official record attempts and switching from CCR to OC for deco as well because the CCRs scrubber durations are going to be inadequate for the full duration of the dive.


If a diver on a 15SAC did a dive OK to 560m he'd be breathing 924lpm so twin 20s would last 9mins. As a result i would have thought CCR was the only viable option at that depth.

ATB

Mark


ATB

Mark

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gathan

COMEX' s HYDRA project had it's divers set an in water record of 534m in 1988. The divers were breathing hydreliox while using SSD equipment, I thought.

In 1992, they performed a dive to 701m while inside the company's sat complex in Marseille. One of the divers actually performed work at that depth for 3 hours.

Andre

Mdemon

I'm surprised no ex-COMEX employees have ever ended up on here. I guess doing it for a living has put them off doing it for fun.

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It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

solocavediver

I think the main problem with very-deep CCR is they never have as little CO2 in the mix as open circuit, and CO2 is very dangerous, killed David Shaw for a start. And that, unlike WOB, cannot be completely engineered out. There's also scary stuff about scrubbers not working so well at depth - exactly how much less, no one seems sure. When we have reliable CO2 monitors on all reputable CCRs I think we may see some more depth records attempted on CCR bounce dives. If you're a saturation diver I'd like to see what they do about CO2 - does lithium hydroxide feature by any chance?

cheers,

Charles.

OceanOpportunity

for deep bounce-type dives, CCRs dont make a heck of alot of sense. From a profile point of view, you are only spending the descent time plus a few minutes max at depth, so why not just do this on OC where there is less to deal with and if you had to bail off the CCR, you'd need the OC anyway? The real advantage of CCR on thee types of bounce dives is during decompression. I'd rather spend 6 hours on my CCR, than juggling 10 cylinders hanging on the line.

For deep dedicated working dives, from a habitat, or in a controlled situation such as a huybrid surface supplied system, CCR makes sense to solve the gas consumption issue while spending considerable amounts of time at depth

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sasmedic

HI there

Firstly I do not know the sweetspot depth range for Rebreather's.

Secondly I must say the 330m OC record has not been accepted as a record as far as I know. There has been controversy about the dive as it was done only a few weeks or months after Nuno Gomes did his 318.25m dive in the Red Sea in 2005. It is easy to claim that a record has been set but to actually prove it is another!!

Based on Nuno's presentation on the record dive the HPNS seems to the big issue wrt going deeper on OC. Nuno planned to go deeper than the 315m tag he retrieved, but feared that he would not be able to retain his DV in his mouth due to the HPNS convulsions he had at that depth. Going deeper would thus depend on an individual's symptomatic onset of HPNS at a certain depth. What makes this area diffficult is the lack of scientific data available to do gas plannning as far as mixes according to certain depths are concerned and the associated deco profile for those gases. Everybody has their own idea of doing it and Nuno's outlook is to be as conservative as possible and has the mental strength (and strong will to survive - as he puts it) to sit under water for 14hours has worked so far.

The planned recovery dive of Dave Shaw had some criticism from international dive experts (presented at the DAN tech diving workshop 2006) that reviewed his rebreather after the fatal attempt as well as the camera footage that was strapped to his helmet. Apparently there was evidence of incorrect sorbent and packing of the scrubber that added to the CO2 toxicity. The work done at that depth by Shaw and getting entangled with out being able to free himself could not be adapted for by the Rebreather technology. And he planned this dive even after he had been treated for DCI on this first dive at Boesmangat in 2004.

When Shaw did not come up for his planned meet, the back up diver for Shaw dived beyond his planned 250m when his buddy inspiration's electronics imploded at about 280m. He then had to go onto OC for ascending and deco and then developed inner ear DCS, supposedly due to the isobaric counterdiffusion theory.

So it seems that for OC attempts the problem is of physiological and gas planning nature and on the Rebreather side it seems like it is the challenge to deal with emergencies that will require hard work as well as problems associated with bailing to OC when the scrubber time is overdue.

I also wondered if there is not a solution that could combine OC and Rebreather for deep attempts?

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fin

I had no idea about this 560m ccr please give what you ve got .
And I must agree that ex-comex are (as most of x-commies) rarely stick around to popular forums. I guess the real world and its 'gangs' is enouqh for them to exchange ideas in 'safe' environment .

OceanOpportunity

physiology is physiology....HPNS is still a very real issue when using deep CCRs.

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MN'07, The Explorers Club

Project Manager, Diving a Dream