The 40% Rule!

[Alshoua-Diver]

Hi guys,

With regards to Nitrox, what is meant by the 40% Rule?
Look forward to your responses. Dean

 

[rcontrera]

I guess that depends on who you are talking to. For Coltri Compressors it means that you can pump up to 40% nitrox through the compressor up to 3000 psi.

I am sure that there are several others so I will defer to the others here.

 

[iain/hsm]

I guess that depends on who you are talking to. For Coltri Compressors it means that you can pump up to 40% nitrox through the compressor up to 3000 psi.

I am sure that there are several others so I will defer to the others here.

Ray.
If Coltri allow users to compress 40% oxygen at 3000psi what percentage do you or Coltri test these compressors on? 60%? or 80%? Its just I never seem to get an answer. Iain Middlebrook.

 

[rcontrera]

40% at 3000 is what they get tested for and that is all they are rated for ... officially. Somewhere a while back some government entity did some testing and came up with the 40% number and it has stuck. I have tried to remember but my old brain has let that information go to make room for more useless drivel.:brain:

I did have a dealer that messed with his Nitrox generator (membrane system) to get 50% and ran that through one of the MCH16 compressors for about a year until it finally blew the third stage head off!

If you are going to try to put through more oxygen than the machine is rated for, you are going to experience earlier than normal compressor failure as the oxygen eats away at the parts and lubricants.

 

[skippy31]

The 40% rule applies not only to compressors but to tanks and regulators. It is generally accepted that tanks and regs should be O2 cleaned if you plan to put more than 40% through or into them.

Tanks especially need to be O2 cleaned if you plan to put 40% or higher O2 content into them since you will have to add pure O2 and top with air or nitrox to get the 40%+ in the tank. Some people choose not to clean regs, but that's not something anyone will officially recommend.

I continuous blend with my Bauer compressor, and I keep the O2 content at 32% I won't go over that because I prefer to stay on the safe side of the 40% rule

Mat.

 

[pescador775]

Contrera, I seem to recall that NASA determined that 50% mix is the threshold whereby EAN starts to behave like pure oxygen. I don't know of any compressor tests specifically. The 40% number for compressors, etc is, like all risk assessment, based on statistics. A lot of compressor simulator testing would have to be done to build a statistical model and that would be expensive. Well, US Divers and some other companies subjected their regulators to some extremely testing and claimed that they proved that a NITROX reg must be O2 cleaned. However, that was a hail Mary pass which would be difficult to duplicate, IMO, and provided no statistical probabilities. The best source of statistics are the divers themselves who gradually evolved a working knowledge and used this in their own problem management. The first brave soul who pumped 40% EAN survived and others followed. There are the Lindbergs and there are the Earharts I know a guy who insisted he was going to use a compressor to jam a welder supply tank with oxygen. On his first (and last) test run he hid behind a barracade. It was fortunate that he did so.

 

[Scuba Duck]

From the Envirodive Gas Blender's Manual:

Historically, the majority of the dive industry has safely followed the standards set by the National Oceanic and Atmospheric Administration (NOAA), and the Occupational Safety and Health Administration (OSHA). These federal organizations, in addition to technical/recreational diving agencies, have an enviable safety record using the 40% guideline.

Any enriched air mixture with an oxygen content of up to 40%, can be treated as air. ​

and​

Any oxygen concentration above this amount must be treated as if it is pure oxygen.​

How does this guideline affect us? What this means is that any part of any gas mixing, storage, or compressor system, that comes into contact with oxygen enriched air with a concentration of oxygen above 40%, requires much stricter protocols in the areas of design, cleaning, and material compatibility.


Blending Oxygen Enriched Air - EnviroDive

 

[Doc Harry]

Remember Apollo 1

Virgil "Gus" Ivan Grissom, Lieutenant Colonel, USAF, deceased
Edward Higgins White, II, Lieutenant Colonel, USAF, deceased
Roger Bruce Chaffee, Lieutenant Commander, USN, deceased

NASA Apollo Mission Apollo-1

~~~~~~~~~~~~~

The Compressed Gas Association does not use the "40% Rule."

According to CGA pamphlet G-4.1 part 11.2.6, it should be the "23.5% Rule." Apparently they feel that the scuba industry takes too many risks using the "40% Rule."

 

[ucfdiver]

For a rec diver, it simply means you cannot have >40% oxygen content in your breathing path that hasn't been o2 cleaned. This includes valves and regulators.

 

[Trimix2dive]

ditto above.