[ RadSafe ] False alarms: was: NYC permitting of detectors

Cary Renquist cary.renquist at ezag.com
Mon Feb 11 12:57:57 CST 2008

On the subject of licensing (training) users rather than licensing
[a few observations]
The nature of the false alarms I received has changed as users are
learning how their 
detectors work...

When DHS first received their detectors (pagers, etc), I used to get
calls in the middle 
of the night about packages coming to us or ones that we sent that were
radiation" (yellow-II/yellow-III packages). 

Now that they have learned how to use the detectors and have received
fancier ones,
a shipment was held up because customs could only see the gammas from
the higher-
energy impurity (<1% of the total activity) coming out of a package and
assumed that the 
item is mislabeled...  (only happened once).  So, the next step is to go
beyond detector
competency and move on to how to look up info on nuclides and make
inferences on 

Some emergency response organizations seem to be stuck in the "if the
meter shows a reading, 
then it must be leaking" mindset.  I can understand this, since most of
the "meters"
that they use are chemical hazard detectors/tubes/etc where there
generally is no background 
reading and packages/etc don't release any measurable quantity unless
there is something 
very wrong.  Perhaps a cheat sheet on how to interpret the Transport
Index that could be attached
to the meters would help, but what they really need is quick access to
somebody who can 
interpret the readings for them.  This is a case where it would be nice
to have a few
people on the hazmat/etc team who are "certified" for rad-detector use.


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Clayton Bradt
Sent: Monday, 11 February, 2008 04:28
To: radsafe at radlab.nl
Subject: [ RadSafe ] False alarms: was: NYC permitting of detectors

Steve Dapra wrote:

"I do not know how many false alarms 
have been answered..."

If a True Positive is taken to be 
detection of a WMD, then we know that 
all of the alarms have been false.  
Since on any given day there are about 
10,000 people in NYC that have had a 
nuclear medicine procedure within the 
past ten days (20,000,000 nuc med 
studies per year in the US prorated to 
population of NYC) and therefore likely 
to set off a police pager, if we assume 
one radioactive WMD plying NYC streets 
daily - then the positive predictive 
value of a positive detect by a police 
pager is about 1/10,000.  For every 
10,000 false alarms each day, there 
would be one True Positive.  That's 170 
man-hours daily just resolving false 
alarms - if we assume just one minute 
is required to resolve each false 

The number of false alarms generated 
by the police themselves is 
overwhelming.  A few additional ones 
from civilians would be 
inconsequential, even if they were 
reported to NYPD.  

The irony is that the civilians using 
radiation detectors are in general far 
more knowlegable in health physics than 
the cops carrying pagers, and so 
unlikely to mistake a false positive 
for a WMD.

Clayton Bradt
dutchbradt at hughes.net

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