3.1 Introduction. 3.1 Introduction

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1 DEPARTMENT OF ARCHITECTURE ABUBAKAR TAFAWA BALEWA UNIVERSITY, BAUCHI ARC 624: ADVANCED BUILDING SERVICES LESSON 3: FIRE DETECTION AND ALARM SYSTEMS IN BUILDINGS 3.1 Introduction 3.1 Introduction 3.2 Conventional fire detection and alarm systems 3.3 Addressable fire detection and alarm systems 3.4 Categorisation of fire alarm and detection systems 3.5 Fire Alarm System Principles 3.6 Building codes for fire detection and alarm systems 3.7 Examples of fire detection and alarm systems 3.8 References Fire detection and alarm systems have several main functions: They provide a means to identify a developing fire through automatic methods. They alert building occupants to a fire condition and the need to evacuate. They commonly transmit an alarm notification signal to the fire department or other emergency response organization. They may also shut down electrical, air handling equipment or special process operations, and they may be used to initiate automatic suppression systems. The requirements depend on the anticipated fire scenario, building and use type, number and type of occupants and criticality of contents and mission. There are 3 common types of systems: conventional, addressable, and analogue addressable systems. Analogue addressable systems are not commonly used Common Abbreviations and definitions AFD EOLR FACP NAC SLC SUFMO Automatic Fire Detection End of Line Resistor Fire Alarm Control Panel Notification Appliance Circuit Signalling Line Circuit Stanford University Fire Marshal's Office Common Definitions 3.2 Conventional fire detection and alarm systems These systems are characterised by the following: They have lower initial equipment costs. Defined location of fire or alarm is not provided at the panel or central station. They can be easier to program. They have limited expansion capability. 1

2 Wiring must be installed in a supervised manner either Class A, or Class B with an EOLR. Alarm/Trouble conditions are annunciated by zone only. Inspection is required to determine the device in alarm or trouble. 3.3 Addressable fire detection and alarm systems These systems are characterised by the following: They are easier to install. More system status information is available at the panel and central station. Input and output programming is much more flexible. There is usually much more room available to expand. Each point on the SLC loop is given a unique address when installed. Alarm or trouble conditions are annunciated by a unique message for each device. 2

3 3.4 Categorisation of fire alarm and detection systems Property Protection Fire Systems These are Automatic Fire Detection (AFD) systems designed to primarily protect property categories. There are two types: P1 P2 AFD installed throughout all areas. AFD installed only in defined areas Life Protection Fire Systems These are Automatic Fire Detection (AFD) systems designed to primarily protect human life categories. There are various types. L1 Manually operated system (M) and AFD installed throughout all areas. L2 AFD installed in defined areas of higher risk of ignition, in addition to L3. L3 L4 L5 M Manually operated system (M) and AFD installed in escape routes and rooms opening into these routes. Manually operated system (M) and AFD installed in escape routes comprising circulation areas and space such as corridors and stairways. A non-prescriptive system in which protected area(s) and/or the location of detectors is designed to satisfy a specific fire risk objective (other than that of L1 to L4). System designed to be operated manually (no AFD). 3

4 3.5 Fire Alarm System Principles Manual Fire Detection Manual fire detection is the oldest method of detection. In the simplest form, a person yelling can provide fire warning. In buildings, however, a person's voice may not always transmit throughout the structure. For this reason, manual alarm stations are installed. The general design philosophy is to place stations within reach along paths of escape/egress. It is for this reason that they can usually be found near exit doors. The advantage of manual alarm stations is that, upon discovering the fire, they provide occupants with a readily identifiable means to activate the building fire alarm system. The alarm system can then serve in lieu of the shouting person's voice. They are simple devices, and can be highly reliable. 4

5 3.5.2 Automatic Fire Detectors Automatic Photoelectric Fire Detectors These are Light Scattering Smoke Detectors. The principle of using a light source and a photosensitive sensor arranged so that the rays from the light source do not normally fall onto the photosensitive sensor. When smoke particles enter the light path, some of the light is scattered by reflection and refraction onto the sensor. The light signal is processed and used to convey an alarm condition when it meets pre-set criteria. Automatic Ionization Fire Detectors This type is better at detecting the smaller amounts of smoke produced by flaming fires. An ionization chamber consists of two plates with a voltage across them, along with a radioactive source of ionizing radiation. Inside the ionization detector is a small amount (about 1/5000th of a gram) of Americium-241. This radioactive element has a half-life of 432 years, and is a good source of alpha particles. They operate on the principle of using a small amount of radioactive material to ionize the air between two differentially charged 5

6 electrodes to sense the presence of smoke particles. Smoke particles entering the ionization volume decrease the conductance of the air by reducing ion mobility. The reduced conductance signal is processed and used to convey an alarm condition when it meets pre-set criteria. Automatic Combination Fire Detectors Combination detectors contain more than one element which responds to fire. These detectors may be designed to respond from either element, or from the combined partial or complete response of both elements. An example of the former is a heat detector that operates on both the rate-of-raise and fixed-temperature principles. Its advantage is that the rate-of-rise element will respond quickly to rapidly developing fire, while the fixedtemperature element will respond to a slowly developing fire when the detecting element reaches its set point temperature. These devices either respond to more than one of the fire phenomena or employ more than one operating principle to sense one of these phenomena. Typical examples are a combination of a heat detector with a smoke detector or a combination of rate-of-rise and fixed temperature heat detector. These devices have listings for each sensing method employed Fire Notification Appliances These are fire alarm system components such as a bell, horn, speaker, light or text display that provide audible, tactile, or visible outputs, or any combination thereof. Audible Notification Appliance A notification appliance that alerts by the sense of hearing. Visible Notification Appliance A notification appliance that alerts by the sense of sight. Initiating device circuits, notification appliance circuits, and signalling line circuits are designated as either Class A or Class B, depending on their performance during nonsimultaneous single circuit fault conditions. Class A Fire Alarm Circuits These are initiating device circuits and signalling line circuits that transmit an alarm or supervisory signal, or notification appliance circuits that allow all connected devices to operate during a single open or a non-simultaneous single ground fault on any circuit conductor. When a single open circuit condition causes a trouble on the panel, all devices on the loop remain operative. 6

7 Class B Fire Alarm Circuits These are initiating device circuits and signalling line circuits that do not transmit an alarm or supervisory signal, or notification appliance circuits that do not allow all connected devices to operate beyond the location of a single open on any circuit conductor. A single open circuit condition causes a trouble on the panel and renders all devices beyond the fault inoperative. 7

8 3.5.4 Types of Fire Alarm Signals Trouble Alarm Alarm type: local sounding (beeping) on Fire Alarm Control Panel (FACP) and Annunciators. Other alarm signals: no horn/strobes sounding or flashing. Caused by: low battery, smoke detector removed, ground fault, open horn circuit, etc. Response: alarm technician responds. Supervisory Alarm Alarm type: local sounding (beeping) on FACP and Annunciators. Other alarm signals: no horn/strobes sounding or flashing. Caused by: sprinkler valve closed, duct detector activated, low-air on pre-action system. Response: fire department responds. 8

9 Fire Alarm Alarm type: all horns and strobes sounding and flashing. Required: building occupants to evacuate. Caused by: smoke detector, manual pull, water flow, duct detector, or heat detector activated. Response: fire department responds Limitation of false alarms Design guidance to minimise false alarms. Systems above 50 detectors to be soak tested False alarm categories include: 1. Unwanted alarm 2. Equipment false alarms 3. Malicious alarms 4. Good intent alarms False alarm rates should be monitored and should trigger an investigation if they exceed recommended limits. 9

10 3.5.6 What Happens When There is a Fire Alarm 4.1 Building codes for fire detection and alarm systems The minimum sound level of a sounder device should be 65 db(a) or 5 db(a) above a background noise (if lasting more than 30 seconds) and at a frequency between 500 Hz 10

11 and 1000 Hz. The maximum sound level should not exceed 120 db(a). BS 5839 Clause Sounder device cabling should be arranged so that in the event of a fault at least one sounder located within the vicinity of the control and indicating panel will remain in operation. BS 5839 Clause The maximum zone floor area should not exceed 2000 m². A person searching a zone for a fire should not have to travel more than 60 m from the zone entrance to identify the source of the fire. BS 5839 Section A person should not have to travel more than 45 m along an escape route to reach a manual call point, when the layout of the building is known. BS 5839 Clause 20.2 The centre of the element of the manual call point should be positioned 1.4 m (+/-200 mm) from floor level (unless a wheelchair user is likely to be the first person to raise the alarm, when this is applicable it should be noted on any certification). BS 5839 Clause 20.2h. Visual alarms such as beacons should always be mounted at a minimum height of 2.1 m from floor level, in a position that is likely to attract attention. BS 5839 Clause 17. Unless MICC or armoured cable to BS7846 standard is used, consideration should be given to the protection of cables against physical damage from floor level to the height of 2 m. BS 5839 Clause For areas where people are sleeping, sounder devices should produce a minimum 75 db(a) at the bed-head with all doors shut. In buildings likely to provide sleeping accommodation for the hearing impaired, consideration should be given to the incorporation of both audio and visual devices. BS 5839 Clause When mounted on a flat ceiling, smoke detection devices have an individual coverage of 7.5 m radius. However these radii must overlap to ensure there are no blind spots. Therefore individual coverage can be represented by a square measuring 10.6 x 10.6 m giving an actual coverage area of 112 m² per device. BS 5839 Clause When mounted on a flat ceiling, heat detection devices have an individual coverage of 5.3 m radius. However these radii must overlap to ensure there are no blind spots. Therefore individual coverage can be represented by a square measuring 7.5 x 7.5 m giving an actual coverage area of 56.3 m² per device. BS 5839 Clause In corridors less than 2 m wide the horizontal spacing of detectors can be increased, the area of coverage need not overlap as in the case of a room. Any corridor over 2 m wide is deemed as a room and must adhere as specified. Please note that heat detectors are not recommended for use in corridors that may be used as escape routes. Vertical shafts like lift shafts and stairways should have a device mounted within 1.5m of any opening. BS 5839 Clause Enclosed stairways should have a detector on the top of the stairway and on each main landing. BS 5839 Clause Cables used for all critical paths, i.e. detector, sounder and the mains supply should be wired in fire resistant cable with a minimum cross sectional area of 1 mm². BS 5839 Clause 26.2j. 11

12 All sounders in a building should have a similar sound, this precludes the mixing of bells and electronic sounders. BS 5839 Clause c. Disabled persons toilets require to be fitted with visual alarm devices. BS 5839 Clause The user of the system should be provided with adequate records and documentation. BS 5839 Clause On completion of each process suitable certification should be provided by the organisations responsible for each stage of the system i.e. design, installation and commissioning. BS 5839 Clause

13 4.2 Examples of fire detection and alarm systems Stanford University 13

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19 4.3 References British Standards Institute (2002). BS 5839:1. Fire detection and fire alarm systems for buildings Part 1: Code of practice for system design, installation, commissioning and maintenance. British Standards Institute. Clymac Fire & Security Systems (2016). BS5839 Part 1:2002 Overview. Available at Cooper Lighting and Safety Ltd (2016). A Guide to BS5839 Part 1:2002. Menon, G. B. & Vakil, J. N. (nd). Handbook on Building Fire Codes. Available at Indian Institute of Technology Kanpur. Singapore Civil Defence Force (2016). Fire Code 2002 Handbooks. Handbook Volume 5, Purpose Group IV, V & VII (Office, Shop & Place of Public Resort) Chapter 6: Fire Fighting Systems. Available at r/download_31/file.res/hb_v5_ch6.pdf. Singapore Civil Defence Force (2016). Fire Code 2013 Handbook (Chapter 6). Available at cations%20and%20circulars/firecode2013handbook/chapter%206.pdf. Tyco Fire Protection Products (2016). Consultant s Guide for Designing Fire Detection & Alarm Systems. Available at ass%20consultants%20guide%20(lr).pdf 19