RE: Smoke Alarms & Photon Beams Don't Mix

[Steve Frey <sfreyohp@SLAC.Stanford.EDU>]

Fellow Radsafers -

Dr. Minnema's suggestion has merit. When deciding, useful 
factors worth considering include 1) ionization-type smoke 
detectors sense the presence of the invisible particles of 
combustion which precede visible smoke and heat when fires 
occur, 2) photoelectric types will alarm only when the fire has 
progressed to the point of visible smoke, and 3) heat detectors 
will alarm only when the fire have progressed to flames leading 
to elevation of the temperature near the detector. 

The generation of carbon monoxide and other toxic gases to 
lethal levels almost always occurs during the initial, 
invisible-combustion-product stage of fires. Accordingly, the vast 
majority of fire fatalities results from asphyxiation, not from burns.  
Keeping this fact in mind can convince even the most hardcore 
anti-atomic-anything fanatics to accept the presence of 
ionization-type smoke detectors in their homes. Photoelectric-type 
and heat detectors can serve better in locations where people 
will not be sleeping and where a desire to minimize the rate of 
false alarms is more important. 

******************************************************
Steve Frey, Head
Operational Health Physics (OHP) Department
Stanford Linear Accelerator Center (SLAC)
Phone:(650) 926-3839 (office),
      (650) 926-3030 (fax),
E-mail address: sfreyohp@SLAC.Stanford.EDU
Any thoughts expressed here are not meant 
to speak for SLAC or any other party in any 
capacity unless so stated.
*******************************************************

At 05:10 PM 2/14/00 -0600, you wrote:
>
>We ran into similar problems in my former life operating a fast burst
>reactor.  Remember that this type of smoke detector uses an ion chamber
>concept - the ionization of smokey air is different from clear air.
>Therefore, anything that ionizes the air in the chamber will set it off.
>(They also work real well when somebody is jack-hammering the concrete floor
>underneath them - believe me, I've been there too :-)
>
>You might consider photoelectric smoke detectors as an alternative, but the
>best solution for us was conversion to heat detectors rather than smoke
>detectors.
>
>Doug Minnema, Ph.D, CHP
>Defense Programs, DOE
><Douglas.Minnema@ns.doe.gov>
>
>what few thoughts i have are truly my own
>
>> -----Original Message-----
>> From:	Chris Alston [SMTP:alstonc@odrge.odr.georgetown.edu]
>> Sent:	Monday, February 14, 2000 5:48 PM
>> To:	Multiple recipients of list
>> Subject:	Smoke Alarms & Photon Beams Don't Mix
>> 
>> >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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>
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Steve Frey, Head
Operational Health Physics Department
Stanford Linear Accelerator Center
Building 24, Room 266, MS 84
2575 Sand Hill Road
Menlo Park, CA 94025
Phone: (650) 926-3839
email: sfreyohp@SLAC.Stanford.EDU
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html