Fire Detector: what are they and how do they work?
Fire detectors are devices designed, in the building field, to detect the presence of a fire inside a building. The word smoke refers to the existence of products derived from inefficient combustion with suspended particles (ashes, among others). In the technical field, it is preferable to speak of fire detectors, since in the case of combustion in which gases are generated, only smoke cannot be spoken of .
Smoke or fire detectors can be analog (they indicate the level of the substance or measured magnitude, for example, the concentration of an element generated during the fire ) or digital (they detect the presence or variation of smoke, but cannot quantify the level). If used in buildings, there are 3 types of smoke or fire detectors:
Conventional detectors. They detect smoke, fire, heat, or any combination of these. They are usually installed in a loop and indicate if there is an alarm in the different detection zones.
Conventional addressable detectors. These systems are also capable of detecting the existence of heat, smoke or fire (or a combination thereof), but they indicate whether there is an alarm for each detection element, not for each zone. Therefore, they are more precise systems that allow a better action of the intervention services.
Smart detectors. In this case, the elements are connected in a loop, but they are able to quantify the presence of smoke , temperature levels, fire or combinations of these elements and react according to a previously programmed protocol.
In buildings, a fire detection system can be considered one that detects the existence of a fire and, in addition, activates the alarm signals necessary to take the appropriate measures. The specific regulations assimilate them to the concept of «automatic fire detection system», called detectors, compared to other manual systems, such as emergency buttons.
Types of smoke and fire detectors
The most widely used detectors are of four types and are based on different physical and operating principles:
Ionic smoke detectors. They work on the principle of ionizing the air in case smoke enters the detection chamber; the detected elements can be invisible to the naked eye. They are generally installed in the chemical industry, as they are more sensitive to fast-growing fires or invisible smoke. It is important to mention that they do not work if the air has a speed higher than about 0.5 m / s.
Optical detectors. The smoke that enters the equipment causes the transmission of a ray of light inside it to be interrupted, which generates an alarm. They are systems for point detection and there are two types; , analog and digital optical detectors. These detectors are placed in the air extraction ducts (ventilation) of the premises to detect the presence of smoke in large rooms or in the building in general. They are commonly used in homes, shopping centers, supermarkets, prisons or warehouses, among others.
Thermal detector. It is not really a smoke detector as such, but a fire detector, since it works by melting an element when an elevated temperature is reached. They are late detection (normally they activate around 68 ºC) and can only be installed in premises up to 7 meters high. Generally, they are used when a conventional smoke detection system cannot be used; for example, in kitchens or garages.
Radiation detector. It is also not a smoke detector, but a fire detector. Detects, through different electronic elements, the presence of radiation generated by the presence of a fire. They are installed only in open rooms or places with very high ceilings, and produce a late alarm.
Depending on the type of detector, a maintenance plan must be established, or another, since some are more sensitive to dirt and can lead to false alarms.
In closed car parks these systems are crucial, since the regulations indicate that they must have a smoke and heat control system. This, in turn, will integrate the ventilation system operating under normal conditions. Smoke detectors, as well as CO or NO 2 detectors , together with the other elements of the control system, allow the ventilation system to be activated as required.
In this area, the most advanced technological solution that exists today is the system that uses impulse fans (or jet fans), manufactured to allow proper operation in case of fire. Axial or centrifugal models are strategically placed along the useful surface of the car park. They distribute the fresh air from the supply points to the extraction points and carry with them the pollution or smoke that may be generated. Likewise, said system can represent savings in construction, installation, and maintenance costs, given the low vertical section of the impulse fans.
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