On Fri, 11 Mar 2005 19:41:30 GMT, HorneTD
wrote:

oreo123 wrote:
What is the difference between photoelectric and ionization smoke alarms?

I know that ionization is used within 15 or 20 feet of steamy bathroom or
kitchen cooktop.

TIA.

Ionization detectors use a small particle of nuclear waste to ionize the

"nuclear waste"? You are not selling the idea of ionization POC
detectors for the home. :-P

smoke particles so that they will conduct a small current. When enough
particles are present in the detectors sensing chamber the detector goes
into alarm.

A photoelectric smoke detector can take two forms one works on
obscuration and the other works on back scatter or reflection. In the
obscuration type the smoke blocks or obscures the light source from the
photoelectric detection cell and the associated circuit drives the alarm
after detecting the loss of light on the photocell. In the back scatter
type the smoke reflects the light from the light source back onto a
photo cell that drives the detector into alarm.

In general the ionization type, which detects the smaller invisible
products of combustion, is quicker to respond to free flaming fuel
limited fires. The photoelectric type, which detects the larger visible
products of combustion, is faster to respond to smoldering or oxygen
limited fires.

Ionization detectors are much more prone to nuisance alarms caused by
cooking, painting, and similar activities.


tom