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FWIW, the Navy's standards for Helium are (from the US Navy Diving =
Manual):
------------------------------------------------------------------------=
-----------------------
4-3.3 Diver's Breathing Helium. Helium used for diver's breathing gas =
shall=20
meet Military Specification, MIL-P-27407B Propellant Pressurizing =
Agent Helium, Type I Gaseous Grade B, Respirable Helium. The =
purity=20
standards are contained in Table4-4.
Table 4-4. Diver's Compressed Helium Breathing Purity Requirements.
Constituent Specification
Helium (percent by volume) 99.997%
Moisture (water vapor) 7 ppm (max)
Dew Point (not greater than) -78=B0F
Hydrocarbons (as Methane) 1 ppm (max)
Oxygen 3 ppm (max)
Nitrogen + Argon 5 ppm (max)
Neon 23 ppm (max)
Hydrogen 1 ppm (max)
Reference: Military Specification MIL-PRF-27407B
------------------------------------------------------------------------=
-----------------------
Acceptable certification of this gas purity is unlikely to be available =
with welding grade He. Doesn't mean the He isn't just as good - just =
means it's not been documented. =20
Using Navy standards to discuss non-military diving may be comparing =
apples and oranges.
B.L. Flank
-----Original Message-----
From: Scott [mailto:scottk@hc*.co*]
Sent: Sunday, October 01, 2000 8:00 AM
To: Capt JT; techdiver@aquanaut.com; Trey
Subject: Re: clarification was: An the beat goes on and on
JT wrote:
> The
> only
> > draw back is what the shop has to pay for the He and then it is =
past on
to
> > the diver, if it was not for the "Lawyers" who would surely say it =
is
> > unsafe in court to make a buck , everyone would be using welding =
gas.
I think this is a bullshit issue, easily shot in the ass.
As far as I know, there is no *law* saying you must use USP gas for =
diving,
the Navy certainly doesn't. I have gas blender shingles from IANTD and =
TDI,
and both texts suggest very strongly that USP be used, but I am aware =
of no
legal requirement. I will concede right now that I could be wrong here, =
and
if I am, would someone with the dope please post it, code and all.
With O2, its remotely possible for a welding shop with crap equipment =
(no
check valves) and idiots at the torches, to back fill acetylene into an =
O2
bottle. Even so, the bottles are evacuated before filling, or we would =
have
some gas suppliers with holes in their buildings. No such problem =
exists
with He. He is used as a shield gas for Tungsten Inert Gas welding =
(TIG),
and is *never* (in my experience) connected to any system that has =
another
gas connected to it, least of all a flammable gas, as He is inert. Any
contaminants in the He would seriously affect weld quality, and since =
He is
used to weld exotic metals (spelled "$$$$") used mostly in Aerospace, I =
have
no problems what so ever with using industrial He. The chances of a gas
supplier getting sued for selling bad gas, and causing an airplane with =
100
people to fall screaming to their deaths, is much more likely than a =
suit
involving SCUBA divers.
We use ABO and industrial grade He.
Scott
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