All about Smoke Detectors!

One of the most important inventions of modern times, the smoke detector saves hundreds of lives every day. As its name suggests, it detects smoke which is actually an indication of fire and then it makes a loud audible sound. It was actually invented by Walter Jaeger, a Swiss physicist. The eureka moment came to him when his actual experiment, which was to make a detector for poisonous gases failed. He then lit up his cigarette to douse his frustration and surprisingly, the smoke triggered the sensor!!! However it took about three decades to make an affordable, compact and portable smoke detector which could also be installed in households. The four types of detectors are:

• Photoelectric detector: This type works by optical detection of smoke. It mainly consists of a source of light like LED (light emitting diode), lens for converging the light rays into a beam and a photoelectric sensor. The sensor is kept perpendicular to the out coming light beam. The phenomena of scattering are utilized for activating the sensor. In the absence of any smoke, the light beam passes without being deviated. In the presence of smoke, the light gets scattered, and some of it reaches the sensor. When ample amount of light is sensed, the alarm is triggered. One of the main advantages of this type of alarm is that it is sensitive to substantial amount of smoke, thus preventing undue hassle due to smoke generated while cooking, which it cannot detect.
• Ionization detector: This type works on the concept of generation of current due to ionization of the atmospheric air. It essentially consists of an ionization chamber and a source for the production of ions. The source is about 0.3µgm of americium-241. It emits alpha radiation which ionizes the air molecules of oxygen and nitrogen. Due to production of unlike charges in the ionization chamber, there is generation of electricity. When small particles of smoke enters the system, it neutralizes the unlike charges, causing a drop in the current triggering the alarm. This type is highly sensitive to even a small amount of smoke.
• Air-sampling detector: It is by far the most efficient type of detector. It has the mechanism to suck in the air which is then passed under a laser which can detect even microscopic particles of smoke triggering the alarm. The main advantage of this type of alarm is that it can measure the degree of smoke and then trigger appropriate alarms ranging from alert to fires.
• Poisonous gas detector: This kind employ sensors to detect the amount of carbon monoxide and carbon dioxide gas in the air, which are the predominant gases evolved during a fire.

Some of the smoke detectors, nowadays, are equipped with water sprinklers which are set off once the alarm is triggered. Smoke detectors should be installed in all public places, and not only that, but also the batteries should be replaced from time to time for proper functioning, because as the saying goes

A stitch in time saves nine!!