RE:Radiological Fume Hood Ventilation

[rkathren@tricity.WSU.edu (Ron L. Kathren)]

For high toxicity materials such as radionuclides, hood face velocities of
at least 125-150 FPM are typically used.  The authority is the American
Conference of Governmental Industrial Hygienists publication "Industrial
Ventilation".  Standard textbooks specify similar face velocities, including
Cember, (2nd ed. p. 327; also 3rd ed. p. 464) who specifies  125-275 FPM;
Kathren (Radiation Protection, p. 144) specifies 125-200 FPM as does Chapter
10 of the Environmental Engineering P.E. Examination Guide and Handbook (p.
408 of the 1996 ed).  The porblem is more complex than simply the hood face
velocity.  Typically, the quantity used in a hood operation should be
limited (10 ALI's is a useful guide).  Perhaps of even greater significance
are the capture velocity and transport velocity, which depend on the
physical form (eg solid particulate, fume, gaseous) and must be sufficient
to effectively provide for contaminant removal.  IMHO, 60 FPM is far too low.

Ron Kathren, P.E., CHP

At 05:47 PM 4/9/99 -0500, Esmeralda Party wrote:
>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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