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Joe · 5th November 2006, 22:37

Quite true Dave.

When was the last time any of us O2 cleaned a second stage and even if you did how could you possibly expect it to remain O2 clean?

Heat is generated going from low pressure to high pressure. Heat is lost going from high pressure to low pressure. Upon entry into the LP chamber(s) the gas is cool, much the same as when you crack a tank valve open more than a trickle and the valve freezes.

Quote: (Originally Posted by Dave Sutton)

Never needed to bail out of a jet or a rebreather.... but fully prepared to do either..

With formal schooling at the degree level in diving science and several years spent as an industrial mixed gas diver using rebreathers every day, my opinions are based on the facts personally observed in the conduct of literally thousands of mixed gas dives *averaging* 500 FSW. In the oil field, what we do as divers for "extreme sport" is a daily job.... just another days dive and depth bonus opportunity.

02 cleaning is a great idea if you are working with *high pressure* 02, but is nonessential in a low pressure environment. Feel free to do it, but low pressure seals in a 02 environment can be lubed with about anything. Feel free to use Halocarbon if you like, but we survived using vaseline or normal siliconme grease at low pressure and reserved Halocarbon for HP regulators and valves where there *was* the potential for high temperatures caused by debris impinging into a sonic velocity gas stream. Ain't nothing else going to cause enough heat for a fire!

In water-pure 02 deco at 40 FSW was observed by me personally for literally *thousands* of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did *much* longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we *never* had a hit. Don't take me wrong: 02 tox *is* an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me.

My only point is to just be reasonable in your approach to these things and let's not all get nuts about "02 compatability of scotchbrite pads", that's all. They are a great tool for many things. Come to think about it, we used them as noise silencers in our helmets too (Divex 3000 and Aquadyne GH-2, each with their umbilical-fed SCC rebreather systems).

Sorry to get off topic.... but it's good data. I only saw two divers die offshore... both due to low PP02 (in one bell-bounce system accident...) but never saw an 02 fire or a 02 tox symptom ever.

Dave

5th November 2006, 22:37	#10 (permalink)
Joe Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Oct 2005 Location: Florida, USA Posts: 247	Re: Filter For OPV Quite true Dave. When was the last time any of us O2 cleaned a second stage and even if you did how could you possibly expect it to remain O2 clean? Heat is generated going from low pressure to high pressure. Heat is lost going from high pressure to low pressure. Upon entry into the LP chamber(s) the gas is cool, much the same as when you crack a tank valve open more than a trickle and the valve freezes. Quote: (Originally Posted by Dave Sutton) Never needed to bail out of a jet or a rebreather.... but fully prepared to do either.. With formal schooling at the degree level in diving science and several years spent as an industrial mixed gas diver using rebreathers every day, my opinions are based on the facts personally observed in the conduct of literally thousands of mixed gas dives averaging 500 FSW. In the oil field, what we do as divers for "extreme sport" is a daily job.... just another days dive and depth bonus opportunity. 02 cleaning is a great idea if you are working with high pressure 02, but is nonessential in a low pressure environment. Feel free to do it, but low pressure seals in a 02 environment can be lubed with about anything. Feel free to use Halocarbon if you like, but we survived using vaseline or normal siliconme grease at low pressure and reserved Halocarbon for HP regulators and valves where there was the potential for high temperatures caused by debris impinging into a sonic velocity gas stream. Ain't nothing else going to cause enough heat for a fire! In water-pure 02 deco at 40 FSW was observed by me personally for literally thousands of hours., right out of the US Navy dive manual and using the tables custom produced for us by Dr. Bill Hamilton..... and we never saw an 02 tox symptom ever. We did much longer 40 foot chamber decompressions (hours) after the in-water portion of the deco was done and never saw an issue there either. Every 6 months each diver did a 60 FSW for 30 minute chamber run on pure 02 for the "02 tolerance test" and in literally hundreds of chamber runs we never had a hit. Don't take me wrong: 02 tox is an issue, just that it's a "fuzzy" limit and not a "hard" one. Go see how the SEALs use LAR-V's for emergency combat escape dives to 75 feet plus (diving in an emergency to below hand-grenade sinking depth) and then talk to me. My only point is to just be reasonable in your approach to these things and let's not all get nuts about "02 compatability of scotchbrite pads", that's all. They are a great tool for many things. Come to think about it, we used them as noise silencers in our helmets too (Divex 3000 and Aquadyne GH-2, each with their umbilical-fed SCC rebreather systems). Sorry to get off topic.... but it's good data. I only saw two divers die offshore... both due to low PP02 (in one bell-bounce system accident...) but never saw an 02 fire or a 02 tox symptom ever. Dave
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