Sean Breheny <shb7@cornell.edu> writes:
> I've seen ionization ones go off from cooking. I've also seen a
> photoelectric one that would go off if you just swept the area with a=20
> broom
> and kicked fine dust into the air.
>=20
> I've also seen an ionization one go off if you just spray a canned
> compressed gas duster into it. I assume that the fluorocarbon gas is=20
> harder
> to ionize (or maybe it is just the fact that there is such a high flow=20
> rate
> that it blows ions out of the way).

	I have also heard the suggestion that you need both types
of detectors.

	I live near the campus of Oklahoma State University which
has, of course, lots of buildings, about 25,000 students on
campus and mostly photo-electric smoke detectors tied to alarm
panels in each building.  They also have a training program in
fire service technology due to a rather big conflagration around
the turn of the last century in which several buildings burned
around Halloween one year so they take fire safety seriously
around here.

	The smoke detectors in student living quarters do go off
for all the usual reasons such as candles and cooking accidents
plus a few false triggers due to shower steam, hair spray, hair
straightening irons and, recently, vaping.

	In the public buildings such as labs, offices and
classrooms, they have false alarms from construction dust and
vigorous custodial activities such as sweeping and vacuuming and
a few odd ones such as the time that a building was the seen of a
false fire alarm several days in a row until somebody noticed that
once each day, photons from our nearest star had a clean path
from the Sun through ninety-three-million miles of space, through
a window in that building and finally to the smoke detector in
question.

	I don't know if this was a new installation or what but
it all lined up twice a year so I don't know what they did to fix
the problem.

	We have also had false alarms that were due to fog
machines which are used for special effects during public events.
The photo-electric smoke alarms flash a light in to a black
chamber and, if something like a cloud of fog or dust is there,
it reflects.

	I would think the ionization type detectors might also
get mixed up over particulates in the air since that would
probably unbalance the comparison between the sealed air sample
and the ambient air sample.

	One year, the city of Tulsa was experiencing ozone alerts
during a stretch of Summer weather and a news reporter from one
of the television stations did a story on the ozone detectors and
interviewed the technician who ran them.  They used an ionization
source and appeared to me to be much like an ionization smoke
alarm.  I believe the report was that ozone caused a different
amount of ionization to show up at the detector.

Martin WB5AGZ
--=20
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