Nitrox Tolerance

[No Waiting]

In September 2006, a new British Standard BS7486:2006 was introduced defining what diver grade oxygen and nitrox is and what the measurement tolerances should be for a particular range of nitrox breathing mixes. This defines the standard for commercially supplied nitrox. For general measurements on site, it is acceptable that the tolerance of percentage of oxygen is within ±1%.


±1% of what? Total mix or the percentage of oxygen? :confused:

So, for Nitrox 32 is the accepted range between 31% and 33% or 31.68% and 32.32%

[Mike Rowley]

±1% of what? Total mix or the percentage of oxygen? :confused:

So, for Nitrox 32 is the accepted range between 31% and 33% or 31.68% and 32.32%

Within + 1% of O2 fraction. Therefore, 29.1% - 30.9% are the acceptable limits for a 30% EANx fill.:)

Cheers

Mike

[No Waiting]

Within + 1% of O2 fraction

For EAN30, the O2 content is 30%, therefore 1% of that 30% is 0.3, that equates to the O2 element of the cylinder being anywhere between 29.7% and 30.3% of the total contents.

Therefore, 29.1% - 30.9% are the acceptable limits for a 30% EANx fillThis is based on +0.9% of the total contents or +3% of the O2 contents :confused:

[deveugle]

+/- 1% of nothing, it is just the amount by which the oxygen percentage is allowed to vary, without having to change your (previously made) calculations.

Think of it just as any other measurement unit, e.g.:

If I order 30g of sugar, I want it within +/- 1g (between 29g and 31g).
If I order 30% of oxygen, I want it within +/-1% (between 29% and 31%).

Hope that helps,
Peter

[PeteM]

For EAN30, the O2 content is 30%, therefore 1% of that 30% is 0.3, that equates to the O2 element of the cylinder being anywhere between 29.7% and 30.3% of the total contents.

This is based on +0.9% of the total contents or +3% of the O2 contents :confused:

It is within 1% therefore techinical 29% is not OK as it is not within it actually is 1%. O2 analysers only analyse to one decimal place so 29.1 is the closest you can get within.

Personal I would not worry about the within/actually differentiation and accept 29 to 31 if asking for 30% and in real life I am less fussy than that

[iain/hsm]

±1% of what? Total mix or the percentage of oxygen? :confused:

So, for Nitrox 32 is the accepted range between 31% and 33% or 31.68% and 32.32%

Are you sure its in BS7486:2006 its just that BS8478:2006 contains similar information. A 1% tolerance based as a percentage of the total gas mixture

Accuracy aside of greater concern is the reduction of the other pollutants allowable in the gas mixture and how the majority of dive shops will not be able to acheive this new standard using there conventional oil lubricated air compressors and double air filters. They simply cannot meet the required standards using oil lubricated air compressors and filters.

Further those few dive clubs and dive shops using these Nitrox membranes will also find they cannot meet standards in so far that in addition to the oil carry over the nitrox permeate produces other concentrated gases such as C02 and Argon and also in greater percentage than the new standard permit.

Again the sports diving industry decision not to use oil free compressor technology and to continue with oily air compressors and base there nitrox production on chemical double filtration (which by its very nature in time fails) is the root of the problem. In the gas industry when dealing with any gas with a percentage of oxygen greater than 23% the answer was and still is "Use no Oil". Iain Middlebrook

[NickMcV]

The resolution of an O2 analyser may be 0.1%, but that is not it's accuracy!

[NickBCotswold]

i was taught its +/- 1% of TOTAL gas (ie +/- 1% of 100%!!)

therefore for nitrox 32, 31-33% is ok!!!

Nick B

[PeteM]

The resolution of an O2 analyser may be 0.1%, but that is not it's accuracy!

That is why I said Analyse to one decimal place rather than accurate to