Ever looked up at the ceiling, saw your smoke alarm and thought, "I wonder how that works?" Well the simple answer is, "With cunning ingenuity". The first thing to understand is that there are two basic designs to a smoke alarm. The first and the most commonly used design is nuclear powered and is known as an ionisation smoke detector, these require little space are cheap and are far more effective than the other type of detector, which is the photoelectric smoke detector. Ionisation Smoke Alarms At the heart of an ionisation smoke detector is a small amount of radioactive material called Americium 241, along with two plates with opposite electrical polarity. This sensor arrangement is held in an air flowing metal chamber and along with its support electronics is powered by a long life battery, usually 9-volt. The metal chamber acts as the negative plate; a positive plate covers the Americium 241. So how does an ionisation smoke alarm work? Alpha particles are generated by the Americium element. These alpha particles ionise the nitrogen and oxygen atoms that circulate through the smoke detector. This simply means that electrons are stripped from both the nitrogen and oxygen elements, when this happens the "air" inside the smoke detector becomes positively charged. These "air" atoms are drawn to the negative (metal chamber) plate, while the negatively charged electrons are drawn to the positive plate. As long as this process continues the smoke alarm will not activate. However, when smoke enters the device it interferes with the ionisation process and the alarm is triggered. Ionisation smoke alarm detectors are considered sensitive enough to do their job correctly and robust enough to last several years under normal circumstances. Should you worry about radioactive Americium 241? Well being radioactive does mean that it produces radiation, however, the amount is very small. Moreover, the type of radiation emitted is in the form of alpha particles, which are the weakest type of radiation. A sheet of paper would stop alpha particles. The metal canister that holds the Americium is more that capable of containing any harmful radiation. You should make sure that any discarded ionisation detectors are properly disposed of, check with your local authority or council to find out the preferred method in your area. Photoelectric Smoke Alarms These are probably the least popular type of smoke detector; this is down to the fact that they're not as sensitive as an ionisation detector. They function by employing two channels; one emits light, while the other channel detects the light. If smoke finds it way into the channels it will interfere with the light and trigger the alarm. Smoke alarms don't just operate as solo devices, you can buy several of them and chain them together, so that if one goes off it alerts all the other smoke detectors in the chain and they also trigger their alarms. What ever you do install a smoke detector today if you don't already have one. They're cheap; easy to fit and could save you and your family's life.
James Gregory reviews and writes about security products. Please visit http://www.sentelsecurity.co.uk/smoke-co-alarms.php to see products mentioned in this article.
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