Weld Leak Check and He
Name: Shadi B.
I am conducting a weld leak check using Helium
gas. However, I don't know what the harmful effects of Helium on the
operators on the work floor, I know it can cause Asphyxia if inhalled
I am thinking of changing from Helium to regular atmosphere,
but I know there are some concerns between the "He" molecule size and the
Atmosphere (different gases) size. can you tell me what the biggest
molecule size in our atmosphere is ("H","O","N", "He"??) and based on
that I will be able to decide weather to use Atmosphere insted of Helium to
conduct my leak check. note that the leak check is being conducted at a
well ventilated area. (shop floor environment)
Helium gas is essentially non-toxic except, as you point out, if it
excludes oxygen. It would be difficult to imagine any realistic conditions
that this would occur in a lab or work floor environment.
You would not be able to substitute another gas for helium in a helium leak
detector because the operating principles of the instrument presumes that
helium is the gas probe. No gas that would be presently "naturally" could or
would work because the atmospheric gasses are always de-gassing from any
Your concern, as a matter of principle, is to be commended. But given the
environment you describe, any hazard is absolutely negligible.
As long as the leak check is conducted in a well-ventilated environment,
helium is an excellent gas to use. Helium is certainly the smallest in size
of all the gases. It is certainly much smaller than any of the components of
air (N2, O2, CO2, Ar). So Helium will leak the fastest, making it the best
operational choice for a leak check.
Helium is also not poisonous.
Its only health risk is that it can displace
air, lowering the oxygen content of what your workers might breathe. Other
gases, such as argon and nitrogen, do this too. In addition, helium rises
rather than sinks, so it will not acccumulate in most confined spaces.
Tha main advantage I could see for using air instead of helium in your
situation is that helium is fairly expensive, while air is essentially free.
But if the performance improvement from helium outweighs its cost, any
safety concerns should not be significant.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
I would not worry about it. Helium is inert. Divers breathe the stuff
(mixed with oxygen, of course) on purpose to avoid the bends.
Anyway, the bigger of the two most abundant molecules in air is N2
(0.31 nanometers). Next is O2 (0.29 nm).
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Update: June 2012