Ionization Smoke Detector

When it comes to fire safety in your home, smoke detectors should always be placed and maintained around your house.

There are two types of smoke alarms, ionization smoke detectors and photoelectric smoke detectors. This hub will concentrate on ionization detectors.

What are Ionization Detectors

Ionization smoke detectors contain an ionization chamber and a tiny amount of radioative material, usually 37 kBq or 1 µCi of radioactive americium-241 (241Am).

The chamber contains 2 plates seperated by a small 1cm gap. A battery within the device supplies a voltage to the plates, it charges one plate positive and the other negative. Alpha particles which are constantly released by the americium-241 knock electrons off of the atoms in the air, which in turn ionizes the oxygen and nitrogen atoms in the chamber.

When smoke particulates enter the air in the chamber the conductivity of the chamber will fluctuate as any smoke that enters the chamber will absorb alpha particles, which will in turn reduce the ionization of oxygen and nitrogen atoms and thus interrupt the current between the plates, it is this interuption that causes the alarm to sound.

An ionization smoke is generally cheaper than a photoelectric detector and it is usually quicker at responding to a flaming fire with smaller particles, however, it is sometimes rejected because it is more prone to false alarms caused by other particles entering the ionization chamber.

With that said both types of detectors have been tested and certified to be used within the home. If you are not sure which type to get, you could install several of each type just to be sure.