Re: Use of Portable Radiation Monitoring Equipment

[Lester.Slaback@nist.gov]

While I have privately responded with an opinion that for the specific
circumstance I think a portable instrument is needed I would like to pose
a question:

For a fixed source facility (so you know the relationship
between the source and the monitor is known) one has the following layers
of safety to prevent an inadvertent exposure:
    1. trained personnel (I alway put brains first.  If you have to
presume you don't have this I would argue you should not have the source.)
    2. an on/off device (switch, key, etc)
    3. status indicators (linked to the source mechanism, not the key)
    4. a door interlock system (not independent if the closure failure is
common to the control system)
    5. an independent area monitor (note: these might not be so
independent if they have to be off to survive source-on radiation
conditions) (note also that the proper functioning of this monitor should
very visually evident to a trained user to obviate
mysterious failures)

So the question is - how many additional layers of prevention are needed?
Presume it is a facility that constitutes a VHRA, potentially lethal
exposures.  If a single operator cannot verify the facility is safe from
the above does a hand held instrument by that same person add any more
confidence to the facility administrator?  Perhaps you should consider
   - two person controls
   - remote verbal confirmation prior to entry
 or other systems that are independent of that single person.

We tend to require more and more, frequently just because it is easy to
do.  Perhaps that is a good enough reason but I suspect at some point it
is detrimental in the sense that an intelligent operator knows it is
overkill and loses the need to think about what he is doing, thereby
negating item 1.

Of course the above is mostly frivolous mental gymnastics since in most
cases your local regulator tells you what to do.

-- 
the above are the personal musing of the author,
and do not represent any past, current, or future
position of NIST, the U.S. Government, or anyone else
who might think that they are in a position of authority.
NBSR Health Physics
NIST
Gaithersburg, MD 20899
301 975-5810
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Lester.Slaback@nist.gov
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