O2 for suit inflation on deep Rebreather cave dives

Janos

If I remember back to my science, I thought the issue of something burning is a a ppO2 issue not a % of O2 issue.

Ie an unsersuit would just be just as likely to catch fire using pure O2 at 10m, as air at 90m.

Of course O2 at 90m is higher still but it's something to consider.

Janos

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Sutty

I suspect the risk of a fire is small. HOWEVER the consequences of a fire are really serious, oxygen filled fabrics burn really well at 1bar, how fast they would burn at 15bar I can only imagine! I very much doubt that you would be able to extinguish the fire by opening the zip before you had major burns, the consequence of 60% burns on a long dive would probably be fatal before you could even get out of the cave. Burns need major amounts of fluid resuscitation due to fluid losses from weeping burns and fluid moving into swelling tissues. Body surface area minus head and hands is about 80% of total surface area. Predicted mortality of burns is age in years + surface area burnt ie 60% burns in a 30yr old=90% mortality.
The idea that a drysuit is damp seems like a good way to reduce the chances of a static electric spark, however the area around the suit feed has had very dry gas passed through it and may be effectively dried enough to be able to generate a spark.
Overall there's no way I'd risk it.

Neil

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Drmike

Your missing the whole point of the exercise. Im talking about deep staged cave dives. Max depth/distance is often restricted by how much deep bail gas (past the last stage point) a diver can physically carry. If I can carry say max 6 bail out tanks with me, as in clipped off on me - I am not about to waste one available tank 'space' with one that I cant even breathe from at depth - makes no sense at all - remember I have to carry O2 anyway. May makes sense only if we are talking about OW dives where a direct ascent is possible and/or when not staging tanks - but thats not what this thread was about.


I guess from the reports of the potential however remote for O2 fires the best thing would be to have a small air tank (never used argon - air is fine) just for suit inflation bungeed to the side of the backplate out the way. I could get one of those small compact suit argon valve thingys. I have a 0.75L tank someplace that would probably work.

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Drmike

ohhh - good point

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Marc T

Not sure, have seen the results of a cigaret's sparks blowed away by the wind on an other people breathin O2 ( in an hospital )
Not serious desease because of many luck, 2nd degree burn only..

Mdemon

If there is a fire then I agree - I don't think the results will be pretty.

As far as sparking goes - is this a red herring? The spark isn't actually anything burning, just energy. Whilst this might ignite flammable gasses, there are none present - O2 isn't. I'm not sure whether there is enough energy in a static spark to actually ignite material, even if surrounded in O2.

Would make for an interesting experiment!

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

SimonK

I suspect that the average undersuit would burn beautifuly in 100% O2, see iain-hsm post 20 above or remember what happened to the Apollo 1 crew? NASA Apollo Mission Apollo-1-- Table of Contents Apollo 204 Review

Certainly climbing out of an drysuit the O2 is going to dissapate rapidly but there will be plenty trapped within the undersuit for a while.

The chances of a fire in suit underwater are probably negligable but I doubt it would be survivable at 30m in open water never mind 100m in a cave and thats before we get to Neils calculation on the long term prospects for a burns victim.

Simon

Mdemon

Yes, I'm sure it will all burn delightfully well once ignited, but my point is that unless you put the cigarette on something in the suit, you aren't going to ignite it. It's not like chucking a bucket of petrol in there and waving a match over it - you have to start the thing burning. And as you put the cigarette in the high O2, it will burn incredibly fast and will probably be out by the time you dropped it. If you lit a match onto the inner suit, then you might see some fireworks, but I don't think you'd be too welcome on the dive boat next time...

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

Dutchy

Now try the following at home.... Take an old fashioned frying pan and put it on an induction cooking plate. Turn up to 12 and wait for it to catch flames. It will happen although there is no fire or flame. My point here is that you don't need a fire to start a fire. Just the old known fire triangle. Fuel, Oxygen and Temperature. But hey you're a CCR diver you knew this allready. The oxygen fires caused by adiabatic heating don't need a flame either.

Fuel? Plenty of that. All the sythetic fabrics work well. In addition their may be plenty of contamination in the form of grease (natural from skin or artificual)
Oxygen? Well yeah at relatively high pressure

Temperature? Hmmmm, well my 37 degrees Celcius or your 100 degrees Fahrenheid is well below the spontenous inflammation point of most materials... The discharge in pure oxygen will not do much (Nitrogen may be oxidized in minute quantities and the 3*O2 will form 2*O3 (=Ozone) but both are endothermic reactions meaning the heath will be absorbed suffocating the reaction. Now the arc won't be in pure oxygen will it? It will start and end at the source off the static electricity.
Theoretically friction may do the job as well but is even less likely... Still pure O2 under pressure and drysuits don't mix well. (Unless off course you have this carbon fiber lined undersuit that gets rid off static electricity before it builds up)
If you don't beleive me then DON'T TRY PROVING IT by inflating your suit at 100m using 100% O2 and press the button of your EMPTY (you need no gas just the sparc) cigarette ligher against your undersuit. You might not survice it if after all I'm right....

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dive2dive2000

I agree with your thought process; 2 out 3 is a dangerous scenario in a fire triangle. Just my PPO2.

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