Ionization vs Optical Smoke Alarm: How to Choose
This article could be useful to you if:
- You have just moved into a new home with no fire alarm system installed.
- Your existing fire alarm system no longer works.
- You previously neglected to install a fire alarm system to your home.
- You wish to extend your fire alarm system to cover more of your property (for example if you have just built an extension or an outbuilding).
Types of Smoke Alarm
Ionization Chamber detectors
The fancy name might suggest otherwise, but this is the simplest and most common type of smoke alarm. They actually contain two small samples of americium-241, which is a radioactive isotope. This radioactive material emits a steady stream of radiation which is disrupted by smoke particles that enter the device.
One piece of the material is in a sealed chamber, the other is exposed to the air where smoke will flow through. The device compares the currents generated by the radiation of each sample and when they differ by a sufficient amount, the alarm goes off.
So, that innocent looking smoke alarm you thought was keeping you safe is actually busy firing radioactive beams; very small amounts and within the alarm casing however, so there’s no risk unless you start taking it apart. Despite the radioactivity, small numbers of smoke alarms can be safely thrown away with the rubbish.
An optical detector just uses a light source and a detector which picks up if dust particles are scattering the light beam. Whilst these types of fire alarm do provide warning for all types of fire, the problem is that they take longer to register the presence of the smoke than the ionization chamber types. A fast igniting flame will be picked up far faster in the ionization type. This is due to the size of the particles within the cloud. A cloud emitted from a slower, smoldering fire has larger particles than a faster igniting flame.
The advantage of using an optical detector however, is that it won’t go off from kitchen fumes and the like that can cause false alarms with the more sensitive ionization chamber type of smoke alarm.
Choosing which smoke alarm to install
You should install optical alarms where harmless fumes will be emitted, such as kitchens or where air circulates with kitchens.
Ionization chamber alarms should be chosen elsewhere due to their increased sensitivity to dangerous fast growing fires. If you’re still worried about the radiation, read this to set your mind at ease.
In our next article we will cover how best to position your smoke alarms.