Re: NCRP/NRC recommendations on dose limits for hot particles

[Mike Lantz <mlantz33@cybertrails.com>]

I would add that the six events that are being discussed are
"calculational" results, i.e., never are they dosimetry measurements.  

I believe that in every case, there is significant question to the true
doses. You almost never know when a particle fell on the skin and
generally conservative estimates are made.  For example, a particle on
PC's could fall on the skin during undressing one minute prior to
entering the PCM's, and the particle may have to be assumed that it was
on the worker's skin for 2 hours. The calculational difference if the
particle was on PC's vs on skin is significant.

Personally, I believe that the 500 rem event, that is always discussed
as the highest ever, has serious questions to its validity.  I don't
think the worker incurred anything near that level.

Bottomline, true high dose events from particles have been rare.

Mike Lantz

mlantz33@cybertrails.com


Bob Flood wrote:
> 
> At 11:57 AM 11/4/1999 -0600, you wrote:
> >I believe that your assessment is incorrect.  Six out of 15,000 is a bad
> >average.  But consider first that half of the overexposures occurred in the
> >early days as hot particles were beginning to become recognized as a hazard.
> >Secondly, the incidence rate is much lower when you consider that the
> >opportunities for exposure would best be characterized by person-hours worked
> >in the radiological environment vs number of TLDs processed.  If 500 Boeing
> >767s have been built and 2 have crashed, that's a bad record.  But when you
> >consider the number of miles travelled or number of flights made, you get a
> >different picture.
> 
> It appears we just disagree. Even if we spread the rate out to 6
> occurrences among 15,000 workers instead of 15,000 dosimeters, it would be
> indicative of a programmatic failure.
> 
> Having participated in those early skin dose assessments during the
> "feeding frenzy" days of hot particle mania, I can also point out that the
> population described refers to the 15,000 DETECTED skin exposures.
> Undoubtedly there where far more exposures that went undetected.
> 
> ===================================
> Bob Flood
> Dosimetry Group Leader
> Stanford Linear Accelerator Center
> (650) 926-3793
> bflood@slac.stanford.edu
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