GAS BLENDING ,,, I JUST DONT UNDERSTAND

[Dyson Diver]

ive a set of exams coming up in the not too distant future ,, so ive been reading back through my notes , and reading a bit on the web. as far as i can see , for partial pressure blending of nitrox i need to be using air to a standarD BS8478
ive been told in the past that as long as your starting to top off a nitrox mix , ie pure oxygen in a o2 clean in date etc etc cyl using partial pressuer blending all i need is double filtered air , seems now , well as of 2006 it has to be BS8478 , does all double filtered air meed this standard , is there a test , how can i tell , ive not seen a sticker on a compressor saying air to BS8478 ,, i have to check cyl test dates , O2 clean etc ,now am i expected to show the air going into the cyl meets this 2006 standard as well.
or is it part of the compressors specs, any help or advice appreciated.
thanks
tom

[buchhawk]

Who are you doing the course with?

[Dyson Diver]

ive allready got my gas blender cert , but i was reading through my bsac notes and found a strange referance that id missed the first time , ill paste it here and see what you think ,

Guidance for BSAC Approved
Gas Blending Centres

Equipment and workshop should meet the following requirements.
1. An installed air compressor system able to safely deliver compressed air for
diving to BS EN 12021. The composition and purity of compressed air is
specified in BS EN 12021.
Note: If compressed air for a diving application is intended for creating a
nitrox mixture this compressed air (also known as “oxygen compatible air”) is
considered to be nitrox and is subject to the requirements specified in BS
8478:2006.
2. BS 8478:2006 is applicable to the production of the following categories of
diving gas mixtures:
a) breathing oxygen;
b) oxygen and nitrogen gas mixtures (known as nitrox);
c) oxygen and helium gas mixtures (known as heliox);
d) oxygen, helium and nitrogen gas mixtures (known as trimix).
3. Other normative references need to be taken into account to meet BS
8478:2006:
a) BS ISO 6145, Gas analysis – Preparation of calibration gas mixtures using
dynamic volumetric methods.

b) HEALTH AND SAFETY EXECUTIVE. Workplace exposure limits. Guidance


just when i thought i had it all sorted out again in my head

[bubbleless]

Air Test Certificate should be on all compressors used for commercial use including club compressors, as this is paid for by the members so you have paid for your air.

BS EN 12021: 1999 Respiratory protective devices.
Compressed air for breathing apparatus

http://www.hse.gov.uk/pubns/dvis9.pdf

BS 8478:2006 is a bit more strict on the levels of impurities I presume but can't seem to find how strict.

Did the compressor you used have a current air cert??

[Dyson Diver]

yes , thats what i thought , but whats this BS8478 , 2006 , is it the new and refreshed version , suitable for partial pressure blending of nitrox . the bsac site mentions both , but it seems to sujest that this bs8478 is a 'cleaner' version of compressed air but reading the document , it reads as if only air to 8478 standards is acceptable for pp blending nitrox.

[bubbleless]

BS8478 , 2006 isn't a revised version of EN 12021: 1999.

Its only for mixing ( clean air)

EN 12021: 1999 is for breathing air (normal air)

[Dyson Diver]

BS8478 , 2006 isn't a revised version of EN 12021: 1999.

Its only for mixing ( clean air)

EN 12021: 1999 is for breathing air (normal air)

then if my reading of the bsac guide is correct , its the only gas standard thats acceptable to be used in nitrox blending .. if thats the case , should all compressors , used in nitrox blending be certed as 8478,,
as yet ive not seen a 8478 sticker on anything .
but
heres another thought
if your carrying a nitrox partial pressure blending factory on your back , ie a rebreather , then shouldnt the dil air be to the 8478 standard too as it is in effect being used in blending with pure o2.
now i really dont understand. as i def havnt even been asked if the air in rebreather cyls meets this new 8478 standard. or are they not included .

[buchhawk]

Ask Dave Vincent @ DV Diving

[bubbleless]

There are different levels allowed by the two standards, one for normal air and the other for mixes or clean air.

The EN 12021: 1999 sets out the criteria for air certs and breathing air, I think the 8478 then goes further with the levels of impurities.

So an air test is done under EN 12021: 1999 but any air used for mixes must pass 8478.

Rebreathers don't use high pressure partial mixing.

You don't breathe off the loop at 232 bar unless your verrryyyyyyy deep.
:0

[stevechesh]

Ask Dave Vincent @ DV Diving

Sorry, didn't catch that!