Types of Systems Used in Fire Alarm Systems
Fire alarms are the first line of defense against fires. Both commercial and residential properties use fire alarm systems that include smoke detectors, heat sensors, and manual pull stations. With the help of a fire alarm system, you can minimize damages and protect property and lives. This article discusses five different types of systems used in fire alarm systems and the way they work. They are as follows:
1) Smoke activated systems
These alarms are frequently found in schools and large office buildings. They detect smoke by using optical sensors to measure the light scattered off particles or by sensing very small changes in air temperature. When smoke is present, the sensor triggers a switch that connects to an electrical circuit connected to the fire alarm. A horn or bell will sound, and a red light will constantly or intermittently blink, depending on the type of system. Before the alarm activates, the amount of time varies from as quickly as 30 seconds for optical alarms to as much as 20 minutes for heat-based ones. However, these types can be problematic because they occasionally are triggered due to dust resulting from construction activities. That is especially true if there is no smoke present.
2) Ionization-Based Systems
These systems detect particles produced by combustion and consist of a very sensitive ionization chamber and a logic system to distinguish between false and valid signals. They can detect minute concentrations of smoke, so they are used in manufacturing areas where there is a risk of fire from materials such as oil or chemicals and in enclosed parking garages, computer rooms, and other areas that may not be occupied very often. A small electrical charge (about 10 volts) runs through the ionization chamber, creating an electric current between two metal plates. If smoke enters the chamber, some particles attach themselves to those plates, thereby reducing the current flow between them—which triggers the alarm. This alarm isn't sensitive to heat (such as that from steam or warm water) and therefore is less likely to false-activate than other types.
3) Water-Activated Systems
A water-activated system is similar to a heat-based one. However, instead of detecting electrical changes in the nichrome wire, it uses another small electric current that passes through two plates submerged in water. The system is activated when hot smoke particles from a fire cause the surrounding air to reach sufficient temperature to break down the insulating layer between the plates, causing them to short circuit and complete the alarm circuit. Water acts as an insulator until it reaches 150° F (65° C). These systems are usually more expensive than others because they require extensive piping throughout the structure being protected. However, they are good for use in areas where there may be steam, since they are very sensitive to small current decreases.
4) Vacuum-Activated Systems
This type is similar to the water-activated system, but instead of water, it uses vacuum space. When hot smoke particles from a fire reach the alarm unit, they cause a diaphragm to open, allowing two plates inside the detector to touch one another and complete an electrical circuit that sounds the alarm. These systems are used primarily for special applications, such as data centers or computer rooms, because they require an airtight volume within the protected area for them to function properly. They can also activate even when there is no visible sign; however, this type of false alarm can be minimized if the system is positioned far from electronic equipment.
In some buildings, it may be necessary to combine more than one of these systems to protect a structure properly. For example, ionization-based systems are often used for spaces with high humidity or where there might be water-based materials that could cause false alarms with heat-activated systems.