Smoke alarms - Lycée Blaise Pascal Rouen

Smoke alarms

, par Jeanss

How can we prevent a family from dying in the fire of their house ?

In France, there are about 12,000 victims of smoke inhalation from fires per year.
So a law has been passed in 2010 in France, making smoke detectors mandatory in all private housing by March 8, 2015.
There are three different types of smoke detectors, the most widespread in the world are :
- The optical or smoke detector
- The ionization smoke detector, which is banned in France especially because it contains a radioactive source.
- The linear smoke detector.

Optical sensor

The photoelectric (or optical) smoke detector is the only type of detector authorized in France. It is the newest and best suited for home fires as it reacts to slow progression fire that may smolder for several hours before we can see the first flames appearing. These fires with slow evolution are also the most many and the most dangerous (for example : A fire caused by a cigarette, ... ) . These sensors are composed of a light emitting diode (LED), an optical chamber, and a photocell. When the smoke reaches the smoke detector, the diode emits a light towards a photocell which in turn produces a current which triggers the sound alarm.

Ionization detector

This sensor consists of two electrodes together with a radioactive element, Americium 241 which gives out alpha radiation. The alpha radiation ionizes the air inside the alarm, and a current flows. If there is smoke in the room, the smoke absorbs the radiation, no current flows and an alarm sounds. Because of its dangerous radioactive element (Americium 241 : a silvery highly electronegative metal. It is part of the actinides family and oxidizes rapidly in the presence of oxygen. It is a compound that is deposited mainly in the skeleton, liver and gonads. The recommended treatment in case of contamination by Americium is the administration of DTPA -diethylene triamine pentaacetic acid-, it is now banned from sale to individuals. ). This is the oldest type of smoke detector, it has existed for over 50 years. It is especially effective for fire with flames. Many European countries prohibit the sale of these detectors because even if very small, they contain a radioactive source. These ionic detectors are banned especially in France.

Linear smoke detector

This sensor operates on the principle of light absorption. The sensor sends light pulses that are reflected by a reflector. The detector measures the level of the reflected signal. A decrease in the signal means a presence of smoke.


For optimal use, it is advisable to put at least one per floor, and to place them at least near the bedrooms and the kitchen. The presence of a detector inside the kitchen can lead to false triggering with simple cooking vapors. It must be placed on the ceiling, about 50 cm away from the entrance of the room to be efficient.
In the presence of smokers, it can be useful to put one in the bedroom, on the ceiling, near the entrance.

A smoke detector is very important for the safety of the inhabitants of a house. They require very little maintenance and are available at very low cost today. Prices may vary from 15€ for the least successful to 100€ for more sophisticated. Its presence will be required, by insurances from 2015 in France, to hope to be compensated after a disaster.

Record of americium-241

Name : Americium Dioxide
Appearance : Solid black crystalline
Empirical Formula : AmO2
Molar mass : 275g/mol
Melting temperature : 1000°C
Density : 11.680kg. m-3
Radioactive Compound