How Do Smoke and Fire Detectors Work?

Smoke and Fire Detectors

Smoke detectors for home use can usually be divided into two types. These are ionization detectors and photoelectric detectors. If you have a smoke alarm in your home, chances are it is one of the two, and possibly even a combination of both. They may use these sensors in addition to a heat detector to warn the resident when there is an alarming amount of smoke in the home, possibly indicating a fire. These alarms may use a 9 volt battery, or the home's electrical wiring in order to function.

Ionization Detectors

The first kind of smoke alarm is the ionization detector. These alarms come with an ionization chamber and some small source of radiation. The radiation produced is a minuscule amount of americium-241. The chamber itself is comprised of two metal plates situated parallel from one another. Electricity charges these plates, with one plate taking a negative charge, and the other positive. Because of the alpha particles released through the radiation, electrons are knocked free of atoms floating in the air, and are naturally attracted to the positive charge of the plate. If smoke enters the machine, it disrupts the charge of the plates, neutralizing them. The electrical current established in the chamber is halted, and this sends a trigger to sound the alarm.

Photoelectric Smoke Detectors

The other type of smoke detector found in the home is the photoelectric device. These devices are more expensive, but quite a bit simpler in their function. In many types of these devices, smoke enters the machine and blocks a beam of light. If this beam is blocked, it will trigger an alarm in the photocells of the machine. Some photoelectric devices work in the opposite way, where a beam of light is scattered by incoming smoke, and certain photocells which should not be receiving light trigger the alarm when they do.

Comparing the Two

Both kinds of smoke detectors must receive the same tests from Underwriter's Laboratory to be certified as safe electrical devices for the home. Therefore, neither is necessarily more effective than the other when it comes to keeping your home safe and putting your mind at ease. Ionization detectors are the less expensive of the two, but they are also the most sensitive. Many people are known to disable the alarms, because they have a tendency to go off even from minor kitchen smoke.

[GilinAtlanta]

on 4/5/2009 Many articles on this subject. Good information.