RE:Radiological Fume Hood Ventilation

[Esmeralda Party <partye@rockvax.rockefeller.edu>]

There isn't a magic number.  We did a review of the subject (E.L. Gershey
et al. in Chemical Health & Safety 3(6):32-39, 1996.) and, as others have
pointed out, there is wide range proposed as acceptable.  More important
than the exact value that you pick for the face velocity is the containment
that you get from the hood.  This is influenced by many factors, among them
traffic by the hood, cross currents from ventilation close to the hood and
how the hood is used (too crowded, etc.).  A check with a smoke tube is a
quick way of getting an idea of how the hood is functioning, but it is not
the definitive answer either.  Many of the measurements are done under
static conditions, but happens when somebody is working in front of the
hood?  We know that there is a lot more to be learned about hoods and how
to evaluate them.  You need to be able to relate information you obtain to
protection factors and at the same time probably make a risk assessment of
the situation.  We don't seem to be quite there yet.




At 04:01 PM 4/9/99 -0500, you wrote:
>I have seen numbers from 60 - 150 fpm, so I don't think you are going to
>find a hard and fast rule.  We use an average of 125 fpm for our "high risk"
>fume hoods where we perform iodinations, use volatile radioisotopes,  or
>work with large quantities and 100 fpm for fume hoods where we use
>radioactive materials that are not readily volatile.  Maybe you could
>appease the researchers by using this "high risk" / "low risk" model.
>
>Patrick Muldoon
>VAMC San Francisco
>
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