Hi, I am currently using this reg but on Air only. i am planning to take up Basic Nitrox since someone is offering it to me almost for free( my suki in PG). We are going to use it for 23% only. do you think its safe to use it without changing O-rings and cleaning it? :blinking: My instructor said that's it OK. But whitetip tech. said otherwise. Do you have Any experience on this?
MK25 G250 is this ok for nitrox?
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ToddK
Contributor
Someone is saying that the reg has to be specially cleaned to go from 21% to 23%?!? I assume this is a typo, and you meant to say 32%? The reg is fine up to 40%, but needs special cleaning if you use mixes richer than that.
NOAA publishes standards for their divers based on a CGA definition of air as having 21 to 23% O2 content. This often gets quoted as the ultimate standard (and it is the most conservative) with the implication that something bad is going to happen if you use nitrox mixes over 23% wiith a reg that has not been specially cleaned.
It is very antiquated thinking that harks back to the early days of nitrox when the industry only grudingly accepted Nitrox - after they figured out there was a ton of money to be made training nitrox divers and selling them new nitrox specific regulators.
It is often a long process to change federal regulations and it is basically is a process that requires all parties to be both motivated and in agreement. And in this case the regs would affect much more than just scuba diving so it is not going to happen anytime soon.
In practice, non O-2 cleaned regs do not detonate or burn up with mixtures under 40% and this has become the industry standard. Special cleaning is felt to be required at mixes of 41% and over, but I suspect that has much to do with the very limited use of mixes greater than 40% for anything other than rebreather diluent and deco gas.
That change in the industry standard does not mean that some shops will stop citing NOAA and CGA standards for air in an effort to keep raking in the extra the cash flow for O2 cleaning regulators and tanks and will not be exposed to mixtures over 40%.
The O2 cleaning is targeted at reducing the possible fuel source for a fire by removing any hydro carbons and by using o-ring materials that have a higher ignition temp. It's a worthy goal, but any fire requires O2 (with more of it available in Nitrox), fuel, and an ignition source and if any of the three is missing a fire will not occur.
O2 by itself is not really the problem in a regulator as a scuba regulator will never have an absolute pressure of more than 300 psi in its intermediate spaces (and that pressure will be less than half that figure at depths where 100% O2 is used) and the partial pressures involved there are not even close to the partial pressures you get inside a scuba tank with air at 2250 to 3500 psi.
Fuel can be reduced but never eliminated as viton and EPDM o-rings that are preferred for O2 use still burn, they just have a slightly higher ignition temperature. And in the case of viton when it does burn it produces phosgene gas - an old freind from WWI trench warfare.
Aircraft O2 systems using 100% O2 have used standard nitrile rubber o-rings for decades in an environment where fire is a major concern - and no one has ever been concerned which says a lot about the suitability of nitrile o-rings in high O2 environments and suggests the EPDM/viton focus is badly overblown. The good news here is that most companies now use EDPM or viton as standard so it is a moot issue.
The other problem with O2 cleaning is that it is a relative term as is the low hydrocarbon content of nitrox and nitrox compatible air. It has less hydrocarbons than grade E air, but they are there none the less and the shop renting nitrox tanks that see perhaps 100-200 fills per year between cleanings are in fact by the last half of the year no cleaner than a regular non-o2 cleaned tank.
What that leaves then for reliable fire prevetion with nitrox is the ignition source. In a regulator fire the ignition source is most often created by the air rushing into the reg and then coming to a sudden stop as the reg pressurizes. This sudden compression creates heat and if high enough it can cause ignition. A much lesser cause would be heat created by high sped gas flow over a rough spot or sharp edge in regulator - but that is exceedingly rare as they are already designed to have passages that create smooth flow whenever possible. Prevention then is simply to pressurize the reg slowly with the purge button depressed to further reduce any sudden compression of the gas.
So while the current approach seeks to reduce the fuels while at the same time increasing the required ignition temp to increase the margin of safety, you can still practically speaking operate an uncleaned regulator (not hideously dirty, but normal wipe it off clean) with nitrile o-rings and 100% O2 and never have a problem as long as you are careful to pressurize the reg slowly to reduce the effects of heating from sudden compression. Welders have been doing just that for well over a century. There is less margin for error, but the practice is not overly dangerous.
The best way to prevent a fire is to simply use good operating procedures by opening the valve slowly while the purge button on the reg is depressed to minimize compression heating and similarly by filling O2 tanks very slowly (50 to 100 psi per minute) to minimize heat from compression. In fact this process is essential to safetey as slamming the valve open on a regulator can in some cases cause a fire even in an O2 clean reg using EDPM or viton -o-rings.
If the industry really took a look at it and actually cared, they would produce nitrox specific valves that open very gradually over the course of a couple turns to make it impossible for a moronic diver to rapidly pressurize the reg. Instead, we have had the reverse where many valves made today offer nearly full flow very quickly - much faster than valves did 20-30 years ago. I suppose this is intended to protect moronic divers who do not know enough to fully open the tank valve.
In any case the key to fire prevetion lies with the diver and their ability to use good operational practices. And if that fails 99% of the time a fire is a non event with a very brief flash fire inside the reg that occurs when the reg is first pressurized prior to the dive. The result is usually charred o-rings that then stop sealing and result in a noticeable leak that the diver detects. The diver would most often not even know a fire occurred until the reg is dissaembled. In fact, I am only aware of one case where the reg catastrophically failed and this was on a rapidly opened valve on a100% O2 deco bottle.
It is very antiquated thinking that harks back to the early days of nitrox when the industry only grudingly accepted Nitrox - after they figured out there was a ton of money to be made training nitrox divers and selling them new nitrox specific regulators.
It is often a long process to change federal regulations and it is basically is a process that requires all parties to be both motivated and in agreement. And in this case the regs would affect much more than just scuba diving so it is not going to happen anytime soon.
In practice, non O-2 cleaned regs do not detonate or burn up with mixtures under 40% and this has become the industry standard. Special cleaning is felt to be required at mixes of 41% and over, but I suspect that has much to do with the very limited use of mixes greater than 40% for anything other than rebreather diluent and deco gas.
That change in the industry standard does not mean that some shops will stop citing NOAA and CGA standards for air in an effort to keep raking in the extra the cash flow for O2 cleaning regulators and tanks and will not be exposed to mixtures over 40%.
The O2 cleaning is targeted at reducing the possible fuel source for a fire by removing any hydro carbons and by using o-ring materials that have a higher ignition temp. It's a worthy goal, but any fire requires O2 (with more of it available in Nitrox), fuel, and an ignition source and if any of the three is missing a fire will not occur.
O2 by itself is not really the problem in a regulator as a scuba regulator will never have an absolute pressure of more than 300 psi in its intermediate spaces (and that pressure will be less than half that figure at depths where 100% O2 is used) and the partial pressures involved there are not even close to the partial pressures you get inside a scuba tank with air at 2250 to 3500 psi.
Fuel can be reduced but never eliminated as viton and EPDM o-rings that are preferred for O2 use still burn, they just have a slightly higher ignition temperature. And in the case of viton when it does burn it produces phosgene gas - an old freind from WWI trench warfare.
Aircraft O2 systems using 100% O2 have used standard nitrile rubber o-rings for decades in an environment where fire is a major concern - and no one has ever been concerned which says a lot about the suitability of nitrile o-rings in high O2 environments and suggests the EPDM/viton focus is badly overblown. The good news here is that most companies now use EDPM or viton as standard so it is a moot issue.
The other problem with O2 cleaning is that it is a relative term as is the low hydrocarbon content of nitrox and nitrox compatible air. It has less hydrocarbons than grade E air, but they are there none the less and the shop renting nitrox tanks that see perhaps 100-200 fills per year between cleanings are in fact by the last half of the year no cleaner than a regular non-o2 cleaned tank.
What that leaves then for reliable fire prevetion with nitrox is the ignition source. In a regulator fire the ignition source is most often created by the air rushing into the reg and then coming to a sudden stop as the reg pressurizes. This sudden compression creates heat and if high enough it can cause ignition. A much lesser cause would be heat created by high sped gas flow over a rough spot or sharp edge in regulator - but that is exceedingly rare as they are already designed to have passages that create smooth flow whenever possible. Prevention then is simply to pressurize the reg slowly with the purge button depressed to further reduce any sudden compression of the gas.
So while the current approach seeks to reduce the fuels while at the same time increasing the required ignition temp to increase the margin of safety, you can still practically speaking operate an uncleaned regulator (not hideously dirty, but normal wipe it off clean) with nitrile o-rings and 100% O2 and never have a problem as long as you are careful to pressurize the reg slowly to reduce the effects of heating from sudden compression. Welders have been doing just that for well over a century. There is less margin for error, but the practice is not overly dangerous.
The best way to prevent a fire is to simply use good operating procedures by opening the valve slowly while the purge button on the reg is depressed to minimize compression heating and similarly by filling O2 tanks very slowly (50 to 100 psi per minute) to minimize heat from compression. In fact this process is essential to safetey as slamming the valve open on a regulator can in some cases cause a fire even in an O2 clean reg using EDPM or viton -o-rings.
If the industry really took a look at it and actually cared, they would produce nitrox specific valves that open very gradually over the course of a couple turns to make it impossible for a moronic diver to rapidly pressurize the reg. Instead, we have had the reverse where many valves made today offer nearly full flow very quickly - much faster than valves did 20-30 years ago. I suppose this is intended to protect moronic divers who do not know enough to fully open the tank valve.
In any case the key to fire prevetion lies with the diver and their ability to use good operational practices. And if that fails 99% of the time a fire is a non event with a very brief flash fire inside the reg that occurs when the reg is first pressurized prior to the dive. The result is usually charred o-rings that then stop sealing and result in a noticeable leak that the diver detects. The diver would most often not even know a fire occurred until the reg is dissaembled. In fact, I am only aware of one case where the reg catastrophically failed and this was on a rapidly opened valve on a100% O2 deco bottle.
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