Another key factor in this huge and rapid penetration of both the market place and the building community has been the development and marketing of low cost detectors by commercial companies. In the early 1970s, the cost of protecting a three bedroom home with professionally installed detectors was approximately 1000 dollars; today the cost of owner-installed detectors in the same house has come down to at least 10 dollars per detector, or less than 50 dollars for the entire home. (nfsa.org) This cost structure combined with effective public education, has caused a huge percentage of American's consumers, whether they are renting or buying, to demand smoke detector protection. The impact of smoke detectors on fire safety and protection is dramatic and can be simply stated. When a fire breaks out, the smoke detector, functioning as an early warning system, reduces the risk of dying by nearly 50 percent. Detectors are most people's first line of defense against fire.
Types of Smoke Detectors.
Ionization detectors have an ionization chamber and a source of ionizing radiation. The source of ionizing radiation is a minute quality of americium-241, which is a source of alpha particles. The ionization chamber consists of two plates separated by about a centimeter. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the americium knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively charged oxygen and nitrogen atoms are attracted to the negatively charged plate, and the electrons are attracted to the positively charged plate, generating a small, continuous electric current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The drop in the current between the plates triggers the alarm.
