Introduction to Fire Detection
Protecting lives and assets from the risk of fire demands a reliable system with well-established products, capabilities, and a dependable track record. Fire detection and alarm systems are installed in buildings to minimize or mitigate the risk and effects of fire. They form part of building services and are designed by the electrical engineering team in collaboration with mechanical engineers to provide a robust detection and suppression systems.
Today, the market offers a wide array of fire detection systems and devices, ranging from simple solutions to highly advanced ones. These modern automatic fire detection systems come in two primary types: conventional and addressable. Conventional systems are typically used in smaller installations, while addressable systems are preferred for larger setups. In Kenya, some of the common brands in the market include Cooper, Menvier, Zeta, Tronic, Asenware, and other lesser known brands.
Fire detection and alarm systems have four primary functions.
- Active Detection
- Monitoring
- Controlling
- Remote Notification
Components of a fire detection system
Control Panel
At the heart of any fire detection system is the control panel, which acts as the central hub. All the devices within the system connect to this panel, which processes signals received from input devices and activates output devices in response. Input devices, such as detectors, measure combustion signals and communicate with the panels, triggering output devices like audible or visual alarms. Fire alarm panels can be further categorized as addressable or conventional, with each serving different needs. Control panels often have integrated batteries and power supply to provide backup when power is lost.
Repeater Panels
These are smaller control panels often wired to the main control panel. They are found in larger sites/buildings where there is a need to display system information at a particular point rather than relying on the main panel only. They come in either active or passive options based on desired functionality.
Smoke detectors
They provide active monitoring of spaces for any smoke coming from burning or smouldering fires. There are two types of smoke detectors.
- Optical Smoke Detectors- Monitor visible smoke particles coming from slow-burning and smouldering fires. They are the best for majority of applications.
- Photo-thermal detectors- These monitor best clean fires and are best suited to areas where there are significant levels of dust or smoke under normal conditions.
Heat Detectors
This device actively monitors the heat levels in a room using heat-sensitive elements. There are two types.
- Rate of rise- monitor the room for rapid change in temperature over a short period and alarm is triggered if the rate is higher than the set value.
- Fixed temperature- this triggers an alarm when heat levels cross a certain set temperature value.
Call Points: These are manual devices with frangible glass element that is broken by people to enable them to raise or activate a fire alarm.
Indicators : These are visual devices that emit bright light signals when the detection devices and alarm system have been triggered
Sounders: Sonders are sound output devices that can produce multiple tones and volume levels when the alarm system is triggered.
Beam detectors: These are applied in spaces with large open areas such as warehouses, indoor arenas, airports etc to detect smoke. They use an optical emitter (projects a beam of light) and a reflective material to sense smoke particles in spaces that range up to 100m.
Air Aspirating Detectors: These detectors use tubes strategically located in buildings to actively collect and deliver smoke to a sensor that can detect smoke particles in the air.
Types of Fire Detection Systems
Different types of fire detection systems are available, tailored to specific applications and building types. These systems can vary significantly in complexity and cost, from a simple setup in a small commercial property to a sophisticated, intelligent addressable system in a multi-occupancy building. A fire detection system comprises detection devices, notification devices, and manual call points. The size of the building dictates the number of detectors required. The system operates by having the control panel receive signals from the detection devices and then transmit signals to the notification devices.
Conventional Systems
This system works well in small-scale structures/buildings. It involves segmenting the building into discrete areas called zones where in each there is a dedicated circuit that connects all the detectors, call points and sounders separately even when in different zones. Zoning allows for easy localization when an alarm is triggered by the control panel.
The detectors and call points are usually conventional types. When the alarm is triggered, the panel indicates the zone which will necessitate manual searching to locate the specific device. Due to this reason, this system is limited to smaller building sizes where the circuitry is relatively small to facilitate the quick location of alarms. Cost-wise, this system is more affordable compared to the addressable one.
Two-wire Systems
The two-wire system is quite like the conventional system above only that the circuitry is different. It combines all the detectors, call points and sounders on a common circuit within a zone. This has the advantage of saving costs due to fewer cable runs required to wire the devices back to the panel. Two-wire systems are the most cost-effective for use in smaller-sized applications.
Addressable Systems
This system, often referred to as intelligent addressable, is different from the systems above due to its ability to uniquely identify all the devices attached to the fire alarm system. The detectors, call points, and strobes are all electronically identifiable by an address which is programmed into them during manufacturing. They are wired into a single circuit often referred to as a loop. The number of devices per loop depends on the type of control panel to be used.
The control panel can establish two-way communication with each device by continuously interrogating in sequence and analyzing responses to determine status. This enables the panel to assess the device’s functionality and the conditions of the area where it is located. Faulty devices can also be singled out for maintenance in advance to prevent failure in the event of a fire outbreak. The ability to have multiple devices installed in a loop across different zones makes addressable systems perfect for mid to large-sized buildings with multiple floors, rooms, and zones.
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