Fire Detection and Alarm System

FIRE DETECTION AND ALARM SYSTEM

Prepared by: Mohd Khairuddin bin Nawi Universiti Tun Hussein Onn Malaysia (UTHM)

INTRODUCTION
What is FIRE?  Fire is essentially a chemical reaction known as combustion  For fire to occur, there must be 3 main component: i. Fuel ii. Heat iii. Oxygen

STAGE OF FIRE
 Ignition- Combustion can be very fast, as in gas explosion or it can be a slow smouldering process  Growth- once started, fire can grow rapidly as it creates the conditions for its own growth. Flashover occurs at this stage  Development- The fire passes through a development stage after the initial rapid growth. At this stage the fire temperature increase slowly.  Decay- At this stage the fire will burn itself out due to lack of oxygen or fuel

HOW DO FIRE SPREAD
 CONVECTION

More than 75% of the combustion products of a fire, e.g. smoke, burning brands, toxic gasses are dissipated in rising convection currents of hot gases at temperatures of 800-100 degree centigrade  RADIATION Radiant heat is a transfer of heat energy as electromagnetic waves.  CONDUCTION The movement of heat through materials such as metals, concrete, piping, etc

CLASSES OF FIRES
 Class A Fire- Involving a combustible solid materials like paper, wool, etc
 Class B Fire- Involving inflammable liquids

like kerosene, diesel, etc  Class C Fire- Involving flammable gases  Class D Fire- Involving reactive metals like sodium and potassium  Class E Fire- Involving ignition of an electrical nature

HOW TO PREVENT FIRE
 PASSIVE APPROACH- under architect and structural engineer’s design: escape routes, fire compartment, fire rating, emergency

lighting, emergency PA, etc
 ACTIVE APPROACH- under M & E systems

like hose reel systems, sprinklers systems, wet riser, etc

Fire detection and alarm system are design to provide warning of the outbreak of fire and allow appropriate the fighting action to taken before the situation get out of control

The design depends on:  Type of building- UBBL Requirement, Bomba Requirements  Type of system to be install  Type of Fire Detection System

UNIFORM BUILDING BY LAWS (UBBL)
 A set of design codes and guidelines to design a building in accordance to an acceptable level as set out to be implemented

to all projects in Malaysia  UBBL not only covers fire requirements but also on other design requirements such as ventilation requirements, toilet facilities, etc  Current gazetted UBBL was published in 1984

SECTIONS IN UBBL RELEVANT TO ACTIVE FIRE PROTECTION SYSTEMS
 PART VIII- Fire alarms, fire detection, fire extinguishment

and fire fighting access (by law causes 225 to 253). Examples: By law 227- Portable extinguishers By law 230- Dry rising systems By law 231- Wet rising systems By law 237- Fire alarm systems By law 243- Fire lift systems
 Third schedule- Ventilation systems (By- Law 41)  Tenth schedule- Table of Requirements for fire

extinguishment, alarm systems and emergency lightning

PLANNING THE SYSTEM
THINGS TO BE CONSIDERED o What type system is proposed? o What action is the system expected to initiate in the event of fire? o How big is the building and what type of building? o Servicing arrangements o Hidden cost to the user

TYPES OF ALARM DETECTION SYSTEM

CONVENTIONAL SYSTEM
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Conventional control panels range in size from 1 zone to over 100 zones. Zones typically consist of some or all of the initiating devices in an area or floor of a building. Some control panels zone capacity is expandable while others are not, limiting its usefulness if a facility adds additional buildings or rooms. Smoke detector to comply BS 5445 Pt7 Heat Detector must comply BS 5445 Pt 5 1977Respond time Manual Break Glass can share the same circuit as detectors The removal of any detector shall not prevent from the operating of any break glass

ADDRESSABLE SYSTEM
 An addressable systems point capacity is

determined by the amount of SLC “Signaling Line Circuits” it contains.
 Each SLC circuit provides power,

FACP

communication, & supervision for all of the devices connected to it.
 Each SLC can accommodate over 100

addressable devices, depending upon the manufacturer.

COMPARISON BETWEEN CONVENTIONAL AND ADDRESSABLE
Conventional
 Lower initial equipment

Addressable
 Easier to install.
 More system status

costs.  Wide range of compatible devices.  Can be easier to program.  Limited expansion capability.

information at the panel and central station.  Input/Output programming much more flexible.  Usually much more room available to expand.

ANALOG ADDRESSABLE SYSYTEM
 Detectors in an analog addressable

systems become “sensors” relaying information to the control panel corresponding to how much smoke or heat that detector is sensing.  The control panel makes the decisions based on this information when to alarm etc.

 Three basic condition to be interpreted by the Control 1. 2. 3. 

Panel: Alarm Condition- Full Scale building evacuation Pre Alarm Condition- Inspection and search for source Fault- Warning need to be repair In order for an analog addressable system to raise alarm, the analog value output by the detector must be in the alarm condition (above the alarm threshold) for a period equal to time taken to complete three successive address sequence (6 seconds)

AUDIO AND VISUAL ALARM
CONCEPT During a fire, if fire alarm system is installed, activation of an alarm sounder is to arouse the attention of the occupants so that the evacuation can be carried out without causing harm to the occupants.

DESIGN GUIDELINE
 Min sound level of 65 dB(A) or 5 dB(A) above the ambient

noise level (whichever is greater) sustainable for a period of min 30 seconds should be produced by the Sounder Unit.
 For Sounder Unit that need to arouse sleeping person, the min

sound level should be 75 dB(A) at bed head with all doors closed
 The type, number and location of fire Alarm Sounders should

be that the alarm sound is distinctive from background noise
 All Alarm Sounders within a building should have similar sound

characteristics
 In areas where a normal type of sounder may be ineffective,

visual alarm signal need to be provided. In general, visual alarm signal should only be used audible alarm, and should not be used on its own

MANUAL CALL POINTS (MCP)
CONCEPT Every fire detection system must include call points, so that in the event of a fire, help can be called immediately.

DESIGN GUIDELINE
 MCP shall be located on exit routes and in particular on  

 

the floor landings or stairways and at exits to open air MCP shall be located so that to raise an alarm, no person in the premises need to travel more than 30 metres MCP shall be mounted at a height of 1.4 metres from the floor, easily accessible, well illuminated and conspicuous positions free from obstruction MCP shall be sited against a contrasting background to assist in easy recognition The delay between operation of a call point and the giving of the general alarm should not exceed 3 seconds

 MCP may be flushed mounted where they

may be seem readily. In locations where they may be viewed from the side (eg. In corridor) they should be surface mounted or semirecessed in order to prevent a side profile area of not less than 750mm2  All colours of the MCP throughout the entire premises shall be of the same colour and shall be n bright red colour unless otherwise approved by the Fire and Rescue Department Malaysia

FIRE DETECTORS
CONCEPT o Fire detectors are designed to detect one or more of the three characteristics of firesmoke, heat and flame. No one type of detector is suitable for all applications and the final choice will depend on individual circumstances

TYPES OF FIRE DETECTOR
Heat Detector
•Fixed Temperature Heat Detector •Rate-of-Rise Temperature Heat Detector •Linear/ Line Detector

Smoke Detector

•Ion Chamber Smoke Detector •Photo Electric Scatter Smoke Detector •High Performance Smoke Detector •Optical Smoke Detector •Aspirating Smoke Detector •Beam Detector

Flame Detector

•Ultra Violet Flame Detector •Infra-red Flame Detector

Automatic Detectors – Photoelectric

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 inter 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 preset criteria

 In the normal case, the light from the light source on the

left shoots straight across and misses the sensor.  When smoke enters the chamber, however, the smoke particles scatter the light and some amount of light hits the sensor

A – Light Source B – Photo Sensor

Automatic Detectors – Ionization
 Ionization smoke detectors use an ionization chamber and a source

of ionizing radiation to detect smoke. This type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts of smoke produced by flaming fires.
 An ionization chamber is very simple. It consists of two plates with a

voltage across them, along with a radioactive source of ionizing radiation.

 The principle of using a small amount of radioactive material to

ionize the air between two differentially charged 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 preset criteria.

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The alpha particles generated by the americium have the following property: They ionize the oxygen and nitrogen atoms of the air in the chamber. To "ionize" means to "knock an electron off of." When you knock an electron off of an atom, you end up with a free electron (with a negative charge) and an atom missing one electron (with a positive charge). The negative electron is attracted to the plate with a positive voltage, and the positive atom is attracted to the plate with a negative voltage (opposites attract, just like with magnets). The electronics in the smoke detector sense the small amount of electrical current that these electrons and ions moving toward the plates represent.

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When smoke enters the ionization chamber, it disrupts this current -- the smoke particles attach to the ions and neutralize them. The smoke detector senses the drop in current between the plates and sets off the horn.

DETECTOR COVERAGE
1. Spacing under Flat Ceiling
o Smoke Detector: max distance every point

7.5m o Heat Detector: max distance is 5.3m

2. Spacing under Pitch Ceiling

If the difference in height between any apex and adjacent valley or low point of the ceiling exceed 600mm for smoke detector or 150mm for heat detector, then the detector should be place on the apex, if less, the ceiling can be considered as flat

3. Spacing in Corridors

In the corridors the constraints of walls cause the hot gas given of by fire to travel faster. Therefore the coverage area is allowed to be bigger

 Ceiling Height

Detector should not be mounted higher than general limits, however the rapid attendance limit shall be accepted under mention condition

Ceiling height limits (m) Detector type

General Limits

Rapid Attendance Limits

Heat detectors (BS 5445:part 5) Grade 1 Grade 2 Grade 3

9.0 7.5 6.0

13.5 12.0 10.5

Point Smoke Detector High Temperature Heat Detector (BS 5445: part 8)

10.5 6.0

15.0 10.5

Optical Beam Detector

25.0

40.0

POWER SUPPLY
TYPES OF POWER SUPPPLY
 Normal Supply  Secondary Batteries  Secondary Batteries with Standby Generator

Normal Supply
 From the public mains, through a private switchboard. In the absence of public power supply, private generated power may be used

Secondary Batteries
 The most commonly used type of standby supply is a secondary battery with an automatic charger
 Where such a battery is used, it should be of a

type having a life span of at least 4 years under the condition of use likely to be experiences inside the fire alarm panel  Batteries capacity should be able to support running ampere of 24 hours supervisory load and 30 min alarm mode

Secondary Batteries with Standby Generator
 In most premises, other than supplies taken from the public mains, an emergency generators is provided which starts

automatically on failure of the normal supply

Battery Calculation
 Formula:

Total Capacity required= ((Max Unsupervised Time + 24 HR) x Operating Current) + (Alarm Current x Alarm Duration)

THE END