Smoke Alarms & Photon Beams Don't Mix

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>Date:         Fri, 11 Feb 2000 15:52:19 -0800
>Sender: Medical Physics Mailing List <medphys@LISTS.WAYNE.EDU>
>From: "David J. Misisco, M. S." <david.misisco@CHOMP.ORG>
>Organization: Community Hospital of the Monterey Peninsula
>
>Here's one for the text books.  We just opened a new center here, new
>vaults, new linacs, etc.  While conducting the radiation survey on the
>second linac, I directed the gantry at 45 degrees in order to make
>measurements outside the room in a public area.  Within seconds of
>energizing the 18 MV photons the fire alarm system went off.  Since this
>was a new facility, we were accustomed to random fire alarm system tests
>and thus ignored the alarms - until the fire department and about 6 guys
>with fire extinguishers came running into the control room.
>
>It seems that the smoke alarm was mounted in the plane of rotation of
>the gantry, and happened in this case to be in the beam during this
>measurement.  The charged particles set in motion by the photons in the
>smoke alarm must have disrupted the alpha particle stream, thus
>simulating smoke.
>
>Well, the fire department was relieved that they didn't have to fight a
>fire, but our engineers are a bit embarrassed.  One to remember the next
>time you have the opportunity to design a new site.
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