Hi, welcome to the topic on Fire Detection and Alarm Systems. This topic forms one of the critical knowledge areas for prospective fire safety manager. As the appointed fire safety manager for a premise, you will need this fundamental knowledge to be able to assess and evaluate your premise fire detection and alarm systems.
At the end of this study topic, you will be able to discuss the design & limitations of fire detection & alarm systems; list & explain the critical system components, and explain the system operations & maintenance requirements.
To achieve these learning outcomes, we will begin by looking at: The System Design and Components of typical fire detection and alarm systems; based on simplified system diagrams and understand how these systems operates; The working principles behind Common Fire Detectors namely, Smoke, Heat, and Flame Detectors; The functions of Fire Alarm Panels; and The Inspection, Test, and Maintenance (ITM) of these systems according to Singapore Standard, SS CP 10.
When we talk about fire prevention, we look at eliminating any possibility of a fire initiating. But when a fire has started inevitably we need to minimize the impact and damage, and fire detection and alarm system is one integral component of the bigger picture in fire protection. The importance and advantage of having a Fire Detection & Alarm System in the premise will enable: Early detection of fires in unoccupied area such as Store Room, Boiler Room, or Server Room; Raise early warning to the occupants so as to facilitate effective evacuation; Fire Alarm Control Unit can also activate other protective systems such as the automatic door closers, door release, stairway pressurization, smoke control, smoke ventilators, or homing of lift system; Including early notification to the emergency services such as the SCDF in local context. In a nut shell, the visuals on your right shows you the purpose of fire detection and alarm system, from detecting the products of fire to raising alarm and notifying monitoring station and eventual emergency services.
As far as detection is concern, mankind has been deploying the manual way - the watchman concept in the nights to patrol crime-prone or fire-prone areas. This included the use of watch-tower overseeing larger area such as forest wild land to spot early sign of forest fire. In today s technology, fire detection has gone into automatic mode, using detector-heads such as network of heat and smoke sensors for early detection of fire products and rapid signalling through wired circuit and wireless technologies. Manual warning or alarming devices are call-points or callout-gong and automatic alarm circuit can now be localized or remotely monitored. Localized Alarm included audible types like electric bells, sirens, or voice messages. Complementing this are visual types such as strobe lights, text messages, and even sensual type vibrating platforms for those occupants who have visual- and audio-disability. Alarm Monitoring Stations can also monitor the status of the system remotely. De- Centralized Alarm Monitoring (or DECAM) Companies are one approach in Singapore providing early activation of emergency services, such as Ademco, ADT, Chubb, Cisco, and Secom. In Singapore, requirements of Fire Detection & Alarm Systems are determined by the Fire Safety Act, Fire Code, and its design and installation in accordance to Singapore Standard, SS CP 10.
Lets take a big picture view of the general system design and its components of Fire Detection & Alarm System.
Simply put, Fire Detection and Alarm System is a network of sensors that detect fire products such as smoke, heat, flame. Some sensors detect the presence of combustible gas in the event of leak or detect flow or pressure drop in a pipeline. All for the purpose of raise fire alert & alarm through some audio & visual devices. The control panel of the system also has actuation function to activate auxiliary protective functions such as smoke control system, opening smoke vent, lowering smoke curtain, homing down lift-cars, closing fire-shutter
The picture is a simplified system diagram of a typical fire detection and alarm system; with a control function to activate auxiliary fire suppression systems (indicated by the boxed up area). The heart of any fire detection and alarm system is the Main Fire Alarm Panel or the Control & Indicating Equipment; capable of analysing the inputs signals and translate into various system actions such as raising status indications for maintenance personnel, or an alarm to alert the occupants. Inputs from the left of the panel are signals from networks of manual call points and detector-heads; these inputs are analysed and translated to system actions such as sounding the alarm devices, transmission to DECAM Alarm Monitoring Station, or activating auxiliary fire suppression system. Any fault or service signals such as running of pumps, faulty circuit, etc. are translated into status indications. Note that all these indications are displayed on the panel for the fire safety manager, maintenance personnel or emergency service personnel to attend to. You will also noticed that in the event of primary power disruption, the system will need to has its own secondary power supply for at least 24 hours in normal monitoring condition, and in addition be capable of supplying the alarm load for at least 10 minutes in the event of an fire alarm during primary power disruption as per SS CP 10 design requirement.
This visual gives you an overview of the system design and system components in a typical fire detection and alarm system. In term of design, fire detection and alarm system is primarily configured: To detect a fire at its early stage of combustion process, sensing products of fire such as Flame, Smoke, and Heat. Emerging technology today has also allowed for Video Smoke Detection (or VSD) To raise alarm upon positive detection, and activate ancillary functions linked to the system, such as homing of lift-cars and smoke control Using control units and devices of conventional-type, addressable-type, or a combination of both called hybrid system. And depending on the type of system configuration, the system components will comprise of: Different specific detector-heads for smoke, heat or flame Linking the detector-heads to the control unit are network of detector circuits The control units are commonly known as the Alarm Panels, such as MAP (Main Alarm Panel) or SAP (Sub Alarm Panel). They are the heart of the system providing analysis and logic algorithm that receive input signals from the various detector-head and detector-circuit, process them and translate into system actions, such as sound the alarm; Thus, linking the alarm devices are network of alarm circuits, that upon receiving action signals will ring the bell, sound the siren, or flashes the strobe light Another standalone alarm circuit is the manual call point that upon actuation sound the local alarm The DECAM panel and DECAM station are usually linked through wired transmission for reliability Likewise, network of wired transmission carry signals to the suppression panel and activate the respective suppression system accordingly. Such as Clean Agent, Inert Gas, Deluge Water Spray, or Water-based Foam Systems Last but not least, the secondary power source that will continue to power the system for the next 24 hours.
This slide shows you a quick glimpse of what is a VSD - Video Smoke Detection System, which is a Camera-based fire detection system suitable for Large Volume Unmanned locations such as ships' holds, engine rooms, rail tunnel, generator rooms on oil-rigs, etc. VSD System analyses video images received from standard CCTV cameras using advanced image processing technology or algorithms to identify motion pattern of smoke; differentiating false-alarm phenomena to actual smoke movement. One of the key advantages of VSD is not relying on proximity of smoke to detector-head; allowing for faster reaction time with relatively good accuracy.
Back to the traditional detector-heads and detector-circuits of Alarm Panel, there are essential 2 types: Conventional or Zonal-Type; and Addressable or Point-Type. Note how the same 10 numbers of detector-heads are wired differently to a conventional panel and an addressable panel respectively. For conventional system: Detectors are wired to the panel in groups known as zone Alarm is identified by zone Detectors indicates either Fire or Normal status only; and System only indicate events but without event recording feature For Addressable system: Each detector is provided with an address that denote specific location Alarm is identified by zone and specific address and location Addressable detector is also able to indicate various condition such as smoke level System capable of indicating events and have recording feature
The visual depicts a typical system diagram of a conventional fire alarm system with 3 zones. Each zone is protected by 1 alarm panel, 6 detector-heads, 3 manual call points, 4 bells, and a link to the sprinkler flow-switch (FS). One of the Alarm Panel acts as the Main Alarm Panel and is linked to monitor status of fire protection system, elevator control, extractor fan, pressurization fans, release door, etc. There is also a link to Alarm Monitoring Station.
The visual although very much similar to the earlier system, depicts a typical system diagram of an addressable fire alarm system with 3 zones. Similarly, each zone is protected by 1 alarm panel, 13 detector-heads, 3 manual call points, and 4 bells. Note that all detector-heads and components are connected in series with each providing a specific address pegged to a specific location. Likewise, one of the Alarm Panel acts as the Main Alarm Panel and is linked to monitor status of fire protection system, elevator control, extractor fan, pressurization fans, release door, etc. There is also computer interface that enable control and status check of each addressable component within the system. There is also a link to Alarm Monitoring Station.
The visual depicts a typical system diagram of a hybrid fire alarm system. A hybrid system is one with combined features of addressable and conventional systems. They can be configured with event recording and alarm management feature from: A basic conventional system with add-on hardwire addressable features, or An addressable system with conventional modules Note how the manual call points and detector-heads are zone-signal connected with individual addressable lines to differentiate the specific location of each component.
One other important aspect about fire alarm system that prospective fire safety manager need to know is that all systems have their advantages and limitation. Some general limitations of Fire Detection & Alarm System include: Fluctuating airflow around the proximity of detector-heads can result in false temperature reading or failure to detect smoke particles; Obstructions to smoke travel, heat & flame radiation may prevent detectorhead from acting quickly System fault that render detector inoperative System switched off for servicing System prone to false alarm leading to genuine alarm being ignored, and Insects invading detector-head triggering false alarm or preventing sensing ability.