Related Products: Fire Protection
There are three common types of fire alarms:
- Thermal Detector - activated by heat
- Ionization Detector - responds to smoke and gas particles from a flaming fire
- Photoelectric Detector - responds to smoke from a smoldering fire
Thermal Detectors
Thermal detectors, used primarily by large commercial or industrial firms, sound only when the temperature rises to a certain level. They are not nearly as safe as the ionization and photoelectric types in that the fire must be more intense before the thermal unit will sound.
However, they might be the best choice for an area where smoke or heat is normally present and might trigger a false alarm, such as near a cooking stove.
Ionization Detectors
Ionization detectors measure the changes in electric current caused by invisible particles ionized in the heat of combustion. They use a non-harmful radioactive source (Americium 241) to transform the air inside them into a conductor of electric current. A small current passes through this "ionized" air. When smoke particles enter the detector, they impede the flow of current. An alarm is programmed to sound when the current gets too low. Ionization detectors respond particularly well to the "smoke" caused by a flaming fire. Since they require very little power, they are effectively powered by household batteries and can be placed almost anywhere in a house (and will work even during a power failure).
Ionization detectors are typically insensitive to smoke from a smoldering fire. And battery-powered models must have their batteries replaced at periodic intervals.
Photoelectric Detectors
Photoelectric detectors involve a small lamp adjusted to direct a narrow light beam across the detection chamber. Next to this light source, but hidden from direct exposure to the beam, is a light-sensitive photocell. Smoke entering the detection chamber scatters the light beam reflecting it in all directions. Some of this reflected light is picked up by the photocell which, at a preset level, triggers the alarm.
A typical photoelectric detector is relatively sensitive to smoke from a smoldering fire (the greatest cause of death in home fires), but reacts slowly to flaming fires-almost opposite of the ionization model.
Most photoelectric models require connection to an electrical outlet. Light bulbs must be replaced every few years.
Fire Protection Recommendations
The Fire Protection Association recommends smoke detectors in every room in the house. The simplest rule for locating a basic smoke detector is mount it between the bedrooms and the rest of the house, but closer to the bedrooms. It is better, however, to install multiple detectors and put one near each sleeping area. In multilevel homes, install one on each level. The basement ceiling, near the steps, is a good location for extra protection. But for the best protection, locate a detector in each bedroom. Smoke detectors have additional features to help in warning the family of fire danger and to help them escape from the house. Some are equipped with lights and are suggested for halls and stairways and any location leading to doors or windows. The idea is to light the escape route. Others have loud sirens to awaken sleeping persons or extra loud horns for use in homes where there are persons with hearing impairment. There are smoke detectors for the hearing impaired with flashing bright lights.
Install each smoke detector on the ceiling or on walls between 6" and 12" below the ceiling. Do not put it within 6" of where the wall and ceiling meet on either surface. This is dead air space with little circulation. Do not mount a smoke detector in front of an air supply or return duct. Related Products: Fire Protection |
National Retail Hardware Association