Re: Personnel Contamination Events

[Bob Flood <bflood@SLAC.Stanford.EDU>]

At 01:39 PM 8/24/1999 -0500, you wrote:
>
>First, an inconsistency.  Why would a program document a PCE for 100 ccpm
on the
>skin of a worker, yet allow the same worker to wear PCs that are 500 ccpm?
 It
>can't be to protect the worker.

When a contamination event happens, 2 things warrant evaluation - the dose
to the subject, and the circumstances that led to the PCE. The dose
evaluation needs to focus primary importance on the amount of contamination
on the person, but the investigation of the circumstances does not.

The justification for interest in the PCE comes from the fact that it isn't
supposed to happen. All the training, surveys, postings, etc are intended
to keep people from being contaminated. Among the tools used for that
purpose are PCs, which are intended to become contaminated instead of the
wearer. So, when contamination is found on PCs, there's nothing wrong -
that's what they are there for. But if a person shows detectable
contamination, something in the system failed, and warrants evaluation.
Since the person got contaminated despite all that is supposed to prevent
it, the fact that the contamination level was 100 cpm and not 50,000 cpm is
more luck than good planning or good practices. And if the cause is not
discovered, it is likely that the same event will happen again, and
eventually the quantity of contamination in such an event will more
substantial. Remember that basis premise of "given enough time, everything
that CAN go wrong WILL go wrong."

>In other words, if 20 hours are spent on
>interviews, survey documentation and the lost time of a worker in the field,
>then perhaps the threshold for documenting a PCE is too low.

In such cases, an evaluation of the opportunity for more serious
contamination should be the means of determining where to cut the
investigation off. If the event seems to involve a location where no
serious contamination was feasible (very small amounts of smearable
contamination), that's quite different from a PCE in a location with 100's
of thousands of dpm smearable. In either case the small quantity on the
person in any one event is not the issue - it's the breakdown in the
planned controls.

===================================
Bob Flood
Dosimetry Group Leader
Stanford Linear Accelerator Center
(650) 926-3793
bflood@slac.stanford.edu
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