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Thread: O2 compatibility at low pressure

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    O2 compatibility at low pressure

    We all know the standard line when it comes to O2 safety and gear: "If it's > 40% O2 in the mix, treat it as pure O2 and make sure everything is O2 clean and compatible".

    But there seems to be a school of unofficial thought floating about that suggests "This really only matters at tank pressures. Once the gas gets out of the 1st stage, it's fiiiiine".

    I realise that no-one but the bravest or most foolish would come out and openly offer that advice on a forum.

    But does anyone here have any evidence/stories to the contrary? Any 8 bar O2 fires, etc? Hint: I'm chasing real stories, not kneejerk reactions out of the PADI manual.

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    Re: O2 compatibility at low pressure

    Quote Originally Posted by Captain Starfish  View Original Post
    We all know the standard line when it comes to O2 safety and gear: "If it's > 40% O2 in the mix, treat it as pure O2 and make sure everything is O2 clean and compatible".

    But there seems to be a school of unofficial thought floating about that suggests "This really only matters at tank pressures. Once the gas gets out of the 1st stage, it's fiiiiine".

    I realise that no-one but the bravest or most foolish would come out and openly offer that advice on a forum.

    But does anyone here have any evidence/stories to the contrary? Any 8 bar O2 fires, etc? Hint: I'm chasing real stories, not kneejerk reactions out of the PADI manual.
    I had the same question in my class. The answer I got was more of a question/self evaluation: "Do you keep your scrubber O2 clean?" The answer of course is no, that's not possible. Since air is floating around, you must believe that hydrocarbons have attached to the scrubber, canister, etc. So the conclusion was at LPO2 (120 psi or so) it isn't an issue. BTW, most don't use O2 compatible lube on orings in the scrubber either- at least they guys I dive with don't. My 2psi worth.

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    Re: O2 compatibility at low pressure

    Quote Originally Posted by whynot?  View Original Post
    I had the same question in my class. The answer I got was more of a question/self evaluation: "Do you keep your scrubber O2 clean?" The answer of course is no, that's not possible. Since air is floating around, you must believe that hydrocarbons have attached to the scrubber, canister, etc. So the conclusion was at LPO2 (120 psi or so) it isn't an issue. BTW, most don't use O2 compatible lube on orings in the scrubber either- at least they guys I dive with don't. My 2psi worth.
    My thinking too, but then again it ain't pure O2 in the loop either. I certainly don't use o2 lube in the loop - scrubber o-rings for me get a wipe of silicon oil every assembly and it seems to slip a lot better than grease.

    I'm more thinking about the IP hose, solenoid connection, 2nd stage on high % O2 bailouts etc... anyone treated one with silicon/buna-n instead of o2 lube and viton, and had it go bang?

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    Re: O2 compatibility at low pressure

    My only un-intentional O2 fire was at full bottle pressure.

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    Re: O2 compatibility at low pressure

    Thanks. And bad luck

    I should add that one of the things that goes along with this question is the rider of always opening the O2 slowly to avoid a shockwave as a potential ignition source.

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    Re: O2 compatibility at low pressure

    Have a think about it when you use an oxy acetelyne set. Both gases coming out the nozzle under pressure, how many times have you ever seen a set self ignite. Risk must be pretty low but is always a possibility

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    Re: O2 compatibility at low pressure

    We have very strict standards for O2 cleaning in the Canadian Navy (almost too restrictive at times) and even our high standards say that O2 at pressures up to 500psi don't require the full treatment of O2 cleaning. We have a modified less stringent procedure for this application and to date we have never had any issues with it. In my opinion there is not enough potential energy in a LP systems to generate enough heat to start a fire. I personally treat LP O2 as if it were air or Tx when it comes to cleaning and use of lubricants.

    Rob

  8. #8
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    Re: O2 compatibility at low pressure

    Thanks folks, I was thinking it all sounded kosher anyway but was wondering if there were any "no, wait, this happened" stories. Sounds like there may not be. The Navy standards info is certainly pointing in a happy direction as far as this is concerned.

    Jolly good!

  9. #9
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    Re: O2 compatibility at low pressure

    Quote Originally Posted by broncobowsher  View Original Post
    My only un-intentional O2 fire was at full bottle pressure.
    So how many "intentional" O2 fires have you started?

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    Re: O2 compatibility at low pressure

    Quote Originally Posted by 4ster  View Original Post
    So how many "intentional" O2 fires have you started?
    In my full cave class we frequently used our O2 leftovers to help get a nice smokey anti-mosquito fire just right :)

    Mexico in May is buggy...

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