History of Smoke Detectors
What is a Smoke Detector?
A smoke detector is a device that detects the presence of smoke in a building and warns the occupants by either sending a signal to Fire alarm control panel or issuing a local audible/ visual alarm from the detector itself, before the fire develops in the building.
In 1970 fatalities from home fires were about 10, 000 a year in North America. After 1970 using smoke detector alarms became more popular and the number of fire fatalities dropped by half by the 1990s. In 1992, , which reports on the new technologies and developments, selected home smoke alarms as one of the 30 Products that Changed Our Lives.
History of the automatic fire alarm and smoke detection
The first automatic electric fire alarm was invented in 1890 by Francis Robbins Upton. Upton was an associate of Thomas Edison. In the late 1930s, Swiss physicist Walter Jaeger tried to invent a sensor for poison gas. He expected that gas entering the sensor would bind to ionized air molecules and thereby alter an electric current in a circuit in the instrument. His device failed: small concentrations of gas had no effect on the sensor's conductivity. Frustrated, Jaeger lit a cigarette and was soon surprised to notice that a meter on the instrument had registered a drop in current. Smoke particles from his cigarette had apparently done what poison gas could not. Jaeger's experiment was one of the advances that paved the way for the modern smoke detector. In 1960 smoke detectors started to be mass produced in the United States. At first, they used in the commercial buildings, but after a couple of years, they entered the residential property space as well.
Smoke Detection Technologies
Ionization smoke detector has a radioactive substance (such as Americium), a sensing chamber and an electronic board. This type of detector ionizes the air in the chamber and these ions act like a bridge for the electrons to pass the air and create a small electric current . At the time of the presence of smoke in the chamber, the ions will attach to the particles and limit their movement between the electrodes and therefore disrupt current flow. The electronic circuit detects the current drop, and triggers an alarm signal. Ionization detectors are more sensitive to the flaming stage of fires which produces smoke with smaller particles.
The photoelectric smoke detector is equipped with a set of a light beam sender and a photoelectric receiver placed in a round plastic chamber. It operates by sending an optical beam to search for smoke in the plastic chamber. When smoke particles enter into the chamber, a photoelectric cell senses the decrease in light intensity and issues an alarm signal. Photoelectric smoke detection is generally reacts most quickly to fires that begin with a long period of smoldering (smoldering fires) that create relatively large amounts of smoke.
There are other methods to detect smoke but the basics are similar to the Photoelectric concept. For long range detection, light sender and receiver should be installed far away from each other (for example in a warehouse) using a laser beam. Laser can travel longer distances without distortion.