All fire detection system require the following basic components: A Control Panel, Cable and devices such as smoke detectors. Here we will explore each device in a bit more detail.
There are 2 basic formats of fire detection systems – conventional and addressable. Conventional is more cost effective and works on zones known as “loops” and will indicate that there is a fire on that loop – but each loop can have a number of devices on it so you may only know there is a fire on the 2 nd floor but not know where exactly.
With an addressable system, you will know exactly where the origin of the fire (or smoke) is but these systems are more costly. The Control panel acts as a control panel of an alarm system does and that is to activate an alarm is fire / smoke is detected. It is important (and a requirement by law) to test your fire detection system at least once a year – although more frequent testing and maintenance is advised.
If you are installing a new fire system, it is important to know that there is still a great deal of cable known as FR20 on the market – going for cheap. Will this cable work? Short answer is yes BUT it's important to know that SANS (South African National Standards) has declared that all new installations need to use the fire resistant cable known as PH120 which will last for 2 hours at 900° Celsius. If you are planning a new installation this type of cable has to be used to remain compliant. If your building has FR20 cable already in it, that is fine but a new install has to be PH120.
Optical Smoke Detector: Using infrared scattering technology, the smoke density can be detected. The detector receives very weak infrared light under normal smokeless condition. If smoke particles enter the chamber, the received light signal will increase by scattering. When smoke density reaches a pre-set level, the detector will alarm out.
Ionization smoke detector: Using a radioisotope to produce ionization in air; a difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smouldering stage. Which is better? Ionisation detectors are typically more cost effective than optical smoke detectors but as mentioned above, optical detectors should detect a fire earlier unless it's already a full flame. It is thus good practice to use a combination of both types of devices a device which combines both types of technologies.
Heat Detectors: Heat detectors come in either a “fixed temperature” or a “raise-of-heat” variants. Pretty self-explanatory, a fixed temperature detector will go into alarm mode if a certain temperature is reached while a raise-of-heat is more measures the ambient temperature and the rate of change. If the change is too much, it will alarm. These types of devices are typically used in kitchens or a workshop where welding would take place and smoke would naturally be present.
Reflected Beam Smoke Detectors: These were designed for spacious rooms, open areas, and high ceilings. They are typically used for large volume areas or areas which have high ceiling such as warehouses and large retail stores and churches etc.
Call Point: This is simply the “red emergency box” which if a person notices a fire will break the emergency glass sending the alarm panel into an immediate alarm – bearing in mind, with normal detectors you would require at least two detectors to detect fire or smoke before sending the panel into and alarm mode – this is known as a “double-knock”.
Strobe / Sounder: If there is a fire, you need to know about it! The device which is going to let you know there's a fire a either a strobe (flashing red light) or a sounder (alarm) or most commonly a combination device which does both.