O2 for suit inflation on deep Rebreather cave dives

Drmike

On some deep and/or long rebreather dives the limiting factor can quite often be the amount of bail out gas a diver can physically carry below the deepest/furthest staged gas point.

Optimising the tanks one carries to ensure max gas volume of breathable gas available to the diver at depth has to be balanced against the potential to overburden the diver with too many tanks making access to gear more difficult and creating more drag and too large a profile. Obviously if you have to carry tanks you want to make sure they all are, if possible, breathable at depth.

The process of optimising/minimising the gas (number of tanks) one carries can lead to such things as running wing inflation off one of the bottom bail tanks (instead of carrying another separate air (not breathable at depth) tank for wing. This however still leaves the issue of suit inflation. Obviously its not possible to run suit inflation of trimix also so this has got me thinking about running the suit off the off-board O2 tank.
(Often offboard O2 is needed on long/deep cave dives to supplement on board O2supply and provide redundancy)


Has anyone much experience using O2 for suit inflation?

If its possible then the diver would carry all bottom trimix bail tanks (one being plugged in as off-board dil for the same reason as the need for off board O2) and one offboard O2 tank.

Anyone know of any potential issues? Has there been any research done on this?

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scunick

Dr Mike,

This was the subject of a discussion recently and one member of the group brought up the issue of potential skin bends. Skin is by definition resident in one or more of the tissue compartments. The salient question is whether skin resides in a tissue compartment that can be supersaturated and therafter off-gass at a rate that matches the rest of your profile.

I have not seen any studies on the impacts of suit inflation gas on overall decompression - would be a really interesting project for a thesis...

oh well ... just my 2c worth.

Dive safe

Nick

abowie

If it was skin DCI you were worried about then exposing skin to hyperbaric O2 in the drysuit might be helpful .

I suspect that the absorption of suit inflation gas is negligable, otherwise argon users would be narced off their faces.

Exposure to O2 might accelerate perishing of seals etc but apart from that it's probably not a big issue.

Personally I wouldn't recommend smoking after your dive though, particularly if posterior "off-gassing" has occurred into the suit during ascent. Might go off with a bang.

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Steve

I'm not saying this from any point of knowledge Mike but something I'd like to be sure of is static in my undersuit. Mine is ofen a bit staticy (new word) and I'd be a bit worried about this being a trigger to ignight my undersuit.

Personally if things are that tight gas wise I would wear a warmer undersuit than needed and use a lean 3mix for suit inflation if that is all that is on offer.

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dave t

Mike

there is one unconfirmed case of a drysuit/undergarment catching fire using o2 as a suit gas (I will see if I can find the report) I used to do it to balance gasses as you suggested but I stopped, just didnt feel right!!!! have no explanation why!

HTH

Dave

UKSteve

Mike,

I dropped a b*ll*ck during my Mod 1 and accidentally switched drysuit inflation and O2 manual addition hoses while kitting up.

It came to light when trying to do manual O2 addition - took me and my instructor a while to figure out why ppO2 dropped each time I pressed the tit. Other than a shredding from all and sundry there were no other side effects with the suit etc... was a Weasle.

Steve

Mdemon

Yes. Been using 100% Industrial Grade O2 in my suit, and occasionally wing, on almost every dive since I got my Inspo. Sometimes I've just used rich nitrox's when using my deco bailout.

On the skin bend issue: From the informal discussions with people who know about these things, I have not found any theoretical issues. I suspect there is a thermal advantage and intuitively think it's better from an ICD perspective, although I have no evidence for this.

What I don't do: I don't usually carry anything electrical (car remote lock) etc, and never flammable (charcoal handwarmers, lighter) inside my DS. If I was to take my GPS/mobile down with me, it would probably go in an Aquapac. I'm not religious about this, I just don't usually take stuff inside my suit. If I do, it's damp in there so I put them in something.

Advantages:
O2 is relatively cheap for me so it saves me using a third cylinder for shallow dives. It allows extra redundant buoyancy - I've switched the Inspo O2 inflator hose onto my DS mid-dive before now when my inflation/lift bag cylinder ran out. That still left the dil to use. If you use O2 in your inflation cylinder, you now have redundant O2, and running out of O2 is worse than a loop flood in my book.

Disadvantages:
Scares people.

My feeling is that inside my DS is a dark, damp, well-earthed environment. There is no obvious source of ignition there. There isn't a great deal of O2/gas in the suit and should the worst happen, I will flood the DS via the neck seal (and disconnect the DS feed). I then have extra buoyancy in my autoblob and gas blob to back up my wing in compensating for the loss of buoyancy if a fire has burnt through the suit.

You can see from the length of time I've been doing this that I don't consider DS O2 fires likely.

I've heard of only one incident using rich nitrox in a DS. The Darwin Candidate decided that a burning charcoal handwarmer was appropriate in a high O2 environment inside his suit...

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Drmike

Perhaps best not to use O2 with an electric suit warmer

Seriously though I only need to find one reference to an O2 fire (not via burning charcoal heater ) and the ideas a no go...anyone?

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montyg

Please excuse the lack of links to back up my suspicion, but I seem to recall that either Nuno Gomes or Dave Shaw used to use O2 as a suit inflation gas...

rgds
monty

Marc T

discussed sometimes ago on a french cave diving foruum: the only potential problem is when using with an electrical heating device.