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Re: respiratory protection
As a NRC licensee, we're bound by 10 CFR 20. A key section re respirator use
is 10 CFR 20.1703(b): "In estimating exposure of individuals to airborne
radioactive materials, the licensee may make allowance for respiratory
protection equipment...provided that the following conditions...are satisfied:
(1) The licensee selects respiratory protection equipment that provides a
protection factor...greater than the multiple by which the peak
concentrations...are expected to exceed the ...[DAC - (formerly MPC)] The
concentration of radioactive material in the air that is inhaled when
respirators are worn may be initially estimated by dividing the average
concentration in air DURING EACH PERIOD OF UNINTERRUPTED USE [emphasis mine]
by the protection factor..." (The omissions are to save space and prevent my
getting carpal tunnel syndrome. I made a good faith effort not to change the
context.) Thus, in planning respiratory protection, you can average out the
puff. This regulation also has ALARA provisions which basically state that
you shouldn't use a given level of respiratory protection if you expect it to
increase the TEDE. This is consistent with the philosophy of the new 10CFR20,
which is to keep the TEDE at ALARA levels. The way TEDE is calculated, it's
the average concentration that counts; it doesn't matter whether it's received
as a puff or as a low level, long-term exposure. On the other hand, IF you
can predict when the puff will occur, eg., when a containment is breached, it
may be ALARA to require respiratory protection for that part of the job.
Bill Lipton
The opinions expressed are strictly mine.
I would like some RADSAFE feed back on the following situation. When
monitoring airborne contamination with CAMs having a continuous display, one
can pin down the time of a "puff" release and observe a spike in airborne
contamination levels. One can also observe that if you change the filter
after the "puff", the airborne level is back down indicating there was short
release and good air clearance. Assume the average airborne level for the
duration of the job is well below what you would recommend as a cut-off for
the respiratory protection you're using (based on the protection factor).
Also assume that for the 10 minute period where you do have airborne
radioactivity, the airborne exceeds the cut-off you have established for
your respiratory protection by a factor of 2 to 5.
If you're simply performing air sampling then your most likely integrating
over the duration of the job and there would be no problem evident. However,
with continuous monitoring you can observe the transient situation. Do you
immediately go up to the next level of resp. protection? Can you live with a
small spike above your protection factor? How big of a spike before it's a
problem? How long? (For the sake of simplicity, ignore all the helpful
advice you would like to give about engineered controls, containment,
contamination control etc.)
I am interested in hearing how radsafers handle time-averaging for airborne
contamination vs. respiratory protection?
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Steve Costigan
ESH-1 Health Physics Operations
PO Box 1663 MS J519 phone: 505-667-0066
Los Alamos National Laboratory fax: 505-667-2964
Los Alamos, NM 87545 e-mail: costigan@lanl.gov
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