Smoke Alarm
Misfired Smoke
I remember this funny incident involving an Indian couple who had just migrated to San Diego. The husband, a software engineer (what else?) and the lady, an amicable housewife moved into our neighborhood. After exchanging the pleasantries and getting to know each other the couple invited us to their house for an Indian dinner. Tempted by the opportunity of tasting exquisite food, we reached at the house next door only to be greeted by a team of Firemen dousing the Kitchen window and a haggard husband consoling his sobbing wife outside the door. To our shock, we encountered the angry Fire chief warning the couple to be cautious in future. Cautious of what?, we asked. The real picture then emerged. The lady, unaware of the smoke alarm in the kitchen had deep-fired some dish and the alert smoke alarm had been set off due to the excessive heat and smoke generated by the process. How do I prepare my food with a Smoke alarm now?, was what the lady asked innocently. She was totally unaware of any concept of Smoke alarm and considered it pretty normal to have a smoke filled kitchen during cooking.
No Fire No Smoke
The lady was lucky for she had at her disposal (though without being aware) the best Fire fighting services and Smoke alarm. However, there are thousands who are not as fortunate and lose life and property due to lack of early warning or prevention lead time through a smoke alarm. But why is a smoke alarm given so much importance when it’s the fire that actually burns everything? Doesn’t it? Yes that’s perfectly true, but even a cursory glance at any fire will tell you that the precursor of fire is always smoke. So, if smoke is detected, it is providing a direct warning of the impending danger.
Let’s delve into the actions that precede formation and full blooming of fire. Fire, as it is commonly known, is formed when three ingredients come together - the fuel, the oxygen and the ignition temperature. The fire, however does not achieve its full glory immediately. Fortunately, it provides many warning signals in the form of cracking noises, smoke generation, and release of hot and ionized air / gases. Now that we have detected the symptoms, all we have to do is find an accurate Smoke alarm and a penetrating cure. It is at this stage of early detection of fire before actually reaching the Ignition point, that the “Smoke Alarms” provide us their services. These Smoke alarms detect the change in atmosphere/ surroundings of the seat of fire using different methods and then the smoke alarm raises an immediate smoke alarm as well as preventive sprinkling systems, if required.
Watching Beyond The Screen
If fire is dangerous then smoke can be very cruel, blinding you and making you clueless and directionless before suffocating you by denying you precious Oxygen. But if the human eye is not able to pierce the smoke screen created by the fire, what smoke alarm can help us in this regard? The Smoke alarm comes forth as a solution to detect the hot gases or smoke itself. Smoke Sensors combine with very loud electronic horn or a smoke alarm to alert people. These smoke alarms just need a 9-volt power supply for functioning. Alternately, the smoke alarms also run on usual household power.
Generally, smoke alarms use two basic principles for detection: The Photoelectric effect and The Ionization effect. The Photoelectric effect is utilized in creating a smoke alarm sensor that consists of a transmitting device which continuously transmits a photo beam. This beam is detected by the receptors (Photoelectric Diode). Thus we have a light source and a light detector. The loop is complete as long as the detector is able to sense the light incident on it. Block this light and the circuit breaks, raising a huge alarm (a really earsplitting sound) - As simple as that!
Now imagine a situation where the arrangement is in place and smoke creates a screen between the source and the sensor/ detector. That’s right! The smoke alarm goes off. Here you have a simple smoke alarm based upon Photoelectric effect. Another smoke alarm uses the same principle albeit in a slightly different way. Instead of the light falling continuously on the detector of the Smoke alarm the light doesn’t fall on it and the circuit is assumed to be complete. When smoke blocks the path and scatters the light beam, a part of it falls on the sensors and off goes the Smoke alarm.
On the other hand, the smoke alarm with an Ionization detector consists of two plates with a voltage cushion between them and an ionizing source (some radioactive material: don’t worry it won’t bombard you with harmful radiations). The alpha particles emitted by the radioactive material inside the Smoke alarm ionize (Remove an electron from the atom thus make available a free electron) oxygen and nitrogen atoms between the plates. The electron (-ve charge) moves towards the +ve charge plate, while the atom (minus one electron) moves towards negative plate. Smoke disrupts the current flow inside the chamber of the smoke alarm i.e. between plates by neutralizing the ions after attaching with them. The current drops drastically due to this action and sensing the drop, the smoke alarm sets off.
The advancements in technologies have ensured miniaturization of the smoke alarm detectors. Thus it is possible to fit an array of these Smoke alarm detectors across the house/ office and also set the smoke alarm to activate the sprinkler by pinpointing the exact location of fire.
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