Posted by JRM on August 06, 2001 at 22:50:06:
In Reply to: Re: Nitrox question - non O2 cleaned cylinders posted by DMU on August 06, 2001 at 22:13:50:
I'm not the expert, but it's late, and I'm stuck here at work babysitting a cranky backup server, so I'll take a shot...
The "petroleum based hydrocarbons" are basically the oil used in the compressor to lubricate it. It isn't some magical stuff. It gets blown into the tank along with the air. It "sticks" to internal surfaces, and can act as an ignition point.
However, the fire triangle has heat, O2, and fuel. Remove any one of the three, and no fire. I've been following this subject for a bit, and have asked several different parties the same questions. To distill it down...
Oxygen cleaning isn't necessarily necessary, as long as one uses common sense. In fact, the solvents commonly used to O2 clean stuff are nasty in themselves. O2 cleaning doesn't mean jack if you pump dirty air into your tank. Is the O2 section of an acetylene torch O2 clean (no)?
However, there are many reasons to go ahead and do it anyway. Who knows what cr*p the dive shop compressor has spewn into your tank. Unless it's a brand new tank, and you can certify every fill it's ever gotten, might want to clean it.
Most shops won't fill tanks unless they have the special blessing, be it O2 service, or whatnot. Not all agree on what the proper blessing should be. Some, if they know you, don't care. They aren't really super knowledgable or experienced. They just don't deal with it enough. A dive shop isn't Praxair (btw, they are a great source of good info, since they deal with this stuff all the time).
And finally, to quote a friend, "Why take the chance?" Is a finger or three really worth the savings from not having the tank cleaned? I don't think so. Besides, you gotta buy Viton O-rings anyway...
So no, you can't clean a tank by draining it. The stuff sticks to the internal surfaces. It's grease. The amount required for ignition is dependent on lots of other variables, among them the flow rate.
Most importantly, don't purge a titanium reg connected to 80%(i think) O2 while it's pointed at your crotch. Bad things happen.
JRM
-- hopefully I didn't miss anything. BTW, my new tanks are in for O2 cleaning as we speak. Anyone wanna part with a pair of keel weights?