At a recent inspection I had a couple questions from the client about smoke detectors and what kind is better. After the discussion, they suggested I answer their question on this blog, so here you go!
There are actually two different styles of smoke detectors: photoelectric and ionization. One type is not better than the other, because they both detect evidence of fire (smoke) differently. This is important because not all fires burn the same.
A photoelectric smoke detector uses a light source and a light sensor. The light source is NOT pointed at the sensor, so when the air is clear, the sensor remains dark. When small particles of smoke enter the chamber, they reflect the light, which will then illuminate the light sensor, which triggers the alarm. Photoelectric sensors are best designed to detect slow burning, or smoldering fires.
An ionization smoke detector has a small amount of radioactive material which is positioned between two electrically charged plates. The radioactive material ionizes the air, and causes current to flow between the electric plates. When smoke enters the chamber, it will disrupt the flow of ions, which triggers the alarm because the flow of electric current between the electrically charged plates is reduced. Ionization smoke detectors are best for rapidly growing or flaming fires.
Most current ionization smoke detectors use americium-241 as their radioactive source. Older units used radium-226 or nickel-63. None of these sources are considered hazardous, and cannot make anything else radioactive. When they reach the end of their life, you can safely dispose of them in normal household trash.
What kind is best?
Since each style of smoke detects different types of fires, to ensure your residence is protected as well as possible, general recommendations are that you have both types of smoke detectors present in your house. Some manufacturers produce units which have both types of detector in the same housing.
Where should smoke detectors be located?
Best practices are that a smoke detector be located on each floor of a residence, one in the common area outside sleeping quarters (this can count as one on each floor as well), and one inside every bedroom. I recommend that you not locate a smoke detector in the kitchen, or directly outside a bathroom. This will reduce nuisance alarms from burned food, or steam from a shower.
Remember to change your smoke detector batteries every SIX months. I recommend changing your batteries when you change your clocks!