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

[Clayton Bradt]

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 
alarm.

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