Sidemount trimix (normoxic) & EAN50 suit gas?

[Subcooled]

Is anyone here using EAN50 as suit inflation gas on trimix dives down to 60m? (ppO2=3.5 ATA)
Fire safety is my concern, not insulation.

I haven't found the need to switch from air to argon yet, and as the EAN50 cylinder will not be staged on my dives, I'd love to skip the inconvenient extra little bottle. Less clutter.

 

[ffdiver]

Why are you concerned with fire safety inflating your suit?

 

[Subcooled]

Because oxygen is very reactive and a high oxygen fraction and a high pressure could lead to spontaneous combustion. Hence, combining oxygen with technical underwear and an dry undersuit made of fiber may carry some risk. 33% and 30m / ppO2 of 1.2ATA doesn't seem to be a problem, I'm doing it all the time, but if we increase the oxygen fraction and ppO2 then the risk may rapidly increase after a certain point.

My question is whether 50% and 3.5ATA is safe or not.

 

[Sidemount_Stu]

Why are you concerned with fire safety inflating your suit?

I'm assuming due to the the elevated ppo2 levels within a rich mix. O2 becomes highly combustible at certain levels.

I would think at 60m a 50% mix would be below any real danger level, but I'm no expert!

I'm sure somebody will be asking shortly with a much more detailed answer!

 

[ffdiver]

O2 doesn't become flammable at any partial pressure. It's an accelerant. You would need a spark to make this a real danger, since the heat you would need for spontaneous combustion would probably hurt you before the o2 in your suit made you into a fire ball. Also remember you will have nitrogen in your suit, which is nonflammable.

I don't think this is a real concern as far as fire safety. You aren't wearing a match head suit pumped with 100% O2. But admittedly this is beyond my expertise.

 

[MXGratefulDiver]

... unless you fart sparks I don't think you have much to worry about ... oh, and I wouldn't put those little hand warmer gel packs inside the suit either ... high levels of oxygen tend to make them hotter ...

... Bob (Grateful Diver)

 

[laurin]

I wouldn't worry about fire safety, apart from maybe avoiding ignition sources right after the dive, as the gas might be absorbed to undies to some degree, and might linger for a while being heavier than air. Extremely unlikely anyway.

However: you'd be carrying an open EAN50 tank way past it's MOD. You'd also be married to the tank, but if you're not planning to stage it that's a minor issue. A 1 liter steel suit tank isn't that inconvenient though, and should be plenty for a square profile to 60m. I wouldn't do the risk trade-off.

//LN

 

[Subcooled]

However: you'd be carrying an open EAN50 tank way past it's MOD

That could be a serious issue, at least if a bottom gas stage tank would be carried too. Tank change gone wrong would kill.
Unpleasant surprises for an OOA diver, too.

 

[nimoh]

I would find that extra hose to be more in the way than an argon bottle. At 60m, I'm guessing you have two deco bottles (50 and 100) and bottle rotation is not a big concern, but if you add a travel bottle, then rotations become problematic.

I guess what it boils down to for me is the right tool for the right job. Not saying you have to do it the way I do it just an opinion.

 

[rjack321]

<face palm>

Ummm so exactly what parts of the fire triangle exist in your suit? (google it if you actually missed this topic in your decompression class)

That should answer your question...