As a  precautionary health measure, we ceased using glass Hg diffusion pumps
anywhere in our Isotope Science Laboratory  about 25 years ago. Their only
advantages which I can think of are being able to see inside the pump and
in rare cases, using one in such a way that reaction with Hg to rid a sample
of some specific contaminants.
In answer to Iain's question, the Hg cycling in the pump per se is not the
problem if  it is properly contained with a foreline trap and a liquid air
trap between the pump and the system.
I believe that problems in the past have been primarily due to (1) a hot
pump cracking  and (2) spills with improper cleanup.  Mercury remaining in
cracks, etc  for years probably generates a number of Hg compounds.  which
are more toxic than the pure metal..
I know of  one case in a stable isotope laboratory where excessive exposure
resulted in years of pain and a premature death. There have been many cases
in other types of laboratories. Hopefully, the history lesson has been
learned!
For most sample preparations, a better quality fore-pump plus a molecular
sieve trap or equivalent serves the purpose. If lower pressure is required,
one can use an oil diffusion pump or a turbomolecular pump.
Roy Krouse



From: "Iain Robertson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, January 25, 2001 10:58 PM
Subject: mercury diffusion pumps


> Dear Isogeochem,
> Yuri's request about diffusion pumps is very topical. We're in the process
of updating several vacuum lines and one of the suggestions is to replace
the mercury diffusion pumps. Could anyone point me in the direction of any
relevant safety guidelines?  The Material Safety Data Sheets state that
mercury is:
>
> "Highly toxic. Long-term exposure to the metal may be fatal. Inhalation
may lead to liver, kidney and CNS damage. Danger of cumulative effects...."
>
> However, is there any information specific to diffusion pumps? Yes, I know
many labs have used mercury pumps for decades without problems! Thanks.
>
> Iain
>
>
>
> *********************************************
> Dr Iain Robertson
> Quaternary Dating Research Unit,
> CSIR Environmentek, PO Box 395,
> 0001 Pretoria, SOUTH AFRICA.
>
> Tel   + 27 12 841 2300
> Fax  + 27 12 349 1170
> *********************************************