Accidental 100% O2 in non O2 clean regs - real risk?

[manni-yunk]

Its the concentration that is material, that will cause a blow out ie explosion. Assisting factors for fire are pressure (ie constant flow), restrictions, adiabatic heating, blocking debris, poor gear design (ie tight bends) and such...Obviously a fast fire in your face is as good as an explosion Id think.

Obviously the concentration is the main concern, But I dont think you can dismiss pressure as immaterial. Arent there less concerns at LP ratings, than at high pressure ratings when it comes to 100% o2?

 

[miketsp]

Obviously the concentration is the main concern, But I dont think you can dismiss pressure as immaterial. Arent there less concerns at LP ratings, than at high pressure ratings when it comes to 100% o2?

I'm pretty sure you're correct, pressure can't be ignored.
Example see page 2 of:

http://www.eiga.org/fileadmin/docs_pubs/Info_15_08.pdf

Ignition temperature is always a function of pressure. After reading this and other articles I'm convinced that the reason I've had no problems is that I always take care to crack the valve extremely slowly and the absolute minimum to pressurize and get flow into the analyzer.
This must reduce nearly to zero the ignition energy from adiabatic compression and even if anything did happen the amount of combustible gas would be very tiny.

 

[maniago]

Obviously the concentration is the main concern, But I dont think you can dismiss pressure as immaterial. Arent there less concerns at LP ratings, than at high pressure ratings when it comes to 100% o2?

I guess it depends on what you are calling LP. Any pressure we have in Scuba is a high enough pressure to cause combustion. But maybe its better to consider the discussion like its Natural gas. If a house fills up with NG and it gets ignited, does the pressure that the gas sitting there matter? Nope. But its concentration does. O2 will spontaneously combust hydrocarbons given enough O2 ie concentration.

 

[manni-yunk]

I guess it depends on what you are calling LP. Any pressure we have in Scuba is a high enough pressure to cause combustion. But maybe its better to consider the discussion like its Natural gas. If a house fills up with NG and it gets ignited, does the pressure that the gas sitting there matter? Nope. But its concentration does. O2 will spontaneously combust hydrocarbons given enough O2 ie concentration.

Spontaneously Combust?????? Really? I do not know if this is accurate. O2 and hydrocarbons together, by themselves and in the absence of some mechanism for heat or ignition source, will not spontaneously combust - you also need to add some sort of heat or ignition.




And - I do not know if your first statement is true either. I can think of numerous examples, in scuba, where pressure would be low enough to not be concerned about the concentration of O2.

 

[Hatul]

I also recall an explosion in San Diego a several years ago when a titanium reg caught fire after the O2 filled tank was turned on. The diver suffered burns. The explanation is likely adiabatic heating of the titanium in the presence of pure O2, titanium having low ignition temperature.

http://www.nitroxdiver.com/Library/explode.html

 

[maniago]

Spontaneously Combust?????? Really? I do not know if this is accurate. O2 and hydrocarbons together, by themselves and in the absence of some mechanism for heat or ignition source, will not spontaneously combust - you also need to add some sort of heat or ignition.
And - I do not know if your first statement is true either. I can think of numerous examples, in scuba, where pressure would be low enough to not be concerned about the concentration of O2.

Ok I'll back off the spontaneous combustion comment as spur of the moment excessive brain fart.
That said, when blending with 100% O2, the recommended fill rate is 60psi or less to avoid any adiabatic ignition. I think we'll all agree that's pretty low compared to anything we do in scuba.

 

[manni-yunk]

Ok I'll back off the spontaneous combustion comment as spur of the moment excessive brain fart.
That said, when blending with 100% O2, the recommended fill rate is 60psi or less to avoid any adiabatic ignition. I think we'll all agree that's pretty low compared to anything we do in scuba.

OK. I think You mean 60 PSI/ minute as a transfer rate - not just a60 psi pressure limitation. I have examples of other very specific things - but I dont want to sidetrack this conversation.

 

[maniago]

You mean 60 PSI/ minute. I have examples of other very specific things - but I dont want to sidetrack this conversation.

Yes, 1psi/sec. Which really is an odd measurement since it should be a flow rate as we use in other gas situations (ie cuft/min) but it seems the industry assumes a standard hose/line cross section that is not explicitly stated. I had a problem with that, but let is go as I found mixology seemed to have a bit more art in it in general...

 

[manni-yunk]

Yes, 1psi/sec. Which really is an odd measurement since it should be a flow rate as we use in other gas situations (ie cuft/min) but it seems the industry assumes a standard hose/line cross section that is not explicitly stated. I had a problem with that, but let is go as I found mixology seemed to have a bit more art in it in general...

I believe there are reasons for PSI vs Cu/ft per minute. Did they not cover that in your class? I know you already took a class - but - the Oxyhacker book is a GREAT resource for this type of information.

 

[kotik]

http://www.eiga.org/fileadmin/docs_pubs/Info_15_08.pdf

Ignition temperature drops with increasing O2 pressure, and the list of materials that will burn gets longer with increasing pressure as well.

Oxygen safety is extremely dependent on pressure--

The age old horror story goes that some guy dove non-O2 clean gear with a high O2 mix and got to 100' before his second stage ignited and blew his lips off.

If he was diving at 100' with a high enough O2 content to blow his lips off, then it's likely that the explosion saved his life...