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According to my gas supplier there's one grade we should definitely avoid, 
namely balloon helium. They receive helium as cryogenic gas and evaporate 
it to fill storage cylinders. The first batches of this distillation 
process will be sold as balloon helium since it tends to contain 
impurities. In some countries they add a little oxygen to balloon helium to 
avoid the risks of hypoxia if people breathe it but that's another issue. 
Expect balloon helium to be impure while all certified grades should be OK. 
Check the specs of welding grade in your country and be particularly 
concerned if it allows CO2. (Typically, impure helium may contain neon, 
methane and CO2).

regards,

Hans

At 04:27 AM 10/1/00 +0100, Aldo P. Solari [APS] wrote:
>Dear senior tech divers:
>
>Some  of  the senior tech divers stated that "welding helium would be
>good for diving mixes/breathing".
>
>In  Canary  Islands (1200 km from nearest euro port), there is no
>"medical  grade"  Helium but there is He for welding (it comes in
>50 Lt tanks and the cost is around 355 USDollars each).
>
>My questions are as follows:
>
>(1) Has any one run any anylses (gas chromatography, whatever) on
>welding grade helium ?
>
>(2)  Those  of you who have used welding grade He: do you use any
>special filters to clean up impurities ?
>
>Any other info would be mostly appreciated.
>
>If  welding  He  is  enough good, it would open up a new world to
>divers on the islands, here.
>
>Thank you for your comments.
>
>cheers,
>
>        aldo
>
>aldo.solari@ho*.se*
>www.ccbb.ulpgc.es/fish-ecology/solaris
>___
>
>
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