FIRE DETECTION AND ALARM SYSTEM

INTRODUCTION Fire detection and alarm system are design to provide warning of the outbreak of fire and allow appropriate fire fighting action to taken before the situation get out of control. The design depends on. A. Type of building –UBBL Requirement, Bomba Requirements. B. Type of system to be install. C. Type Of Fire Detection System.

DESIGN REQUIREMENTS Codes & Standards Automatic fire alarm system shall be design based on B.S 5839 part 1 ~ part5: 1988, UBBL 1984 TENTH SCHEDULE. Others standard LBS 1014 Loss Prevention Certification Board

PLANING THE SYSTEM Things to be considered. What type system is proposed? What action is the system expected to initiate in the even of fire? How big is the building and what type of building? Servicing arrangements. Hidden cost to the user.

SELECTING THE TYPE OF COVERAGE Discussion with building owner, fire authority regarding to type of protection to be established for the particular building is crucial. British Standard 5831 Part 1 1988 provide a on coding system which allow fire detection and alarm system design to be specified according to purpose and the extent of protection to be afforded.

SELECTING THE TYPE OF COVERAGE Classification of system 1. Manual Type (Type M)-System which provides manual alarm only. 2. Life Protection (Type L)-System which provides for the protection of life that is the safety of occupants.

SELECTING THE TYPE OF COVERAGE Detection of fire. Initiate an alarm of fire. Provides sufficient time for occupants to escape Type L3-Covers escape routes and adjoining room (detectors) should be situated on to the escape routes.

SELECTING THE TYPE OF COVERAGE Type L2-Covers escape routes and adjacent rooms and any other areas where it is considered the occupants are vulnerable. Type L1- Total Coverage.

SELECTING THE TYPE OF COVERAGE Property Protection (Type P) Automatic detection of fire. Initiate an alarm of fire Indicate the location of fire within the premises Type P2 covers all high risk area Type P1 Total coverage.

HOW TO CONFIGURE ZONE WITHIN PREMISES What is fire zone? The most positive and effective where of limiting fire spread within the building is to subdivide it into the smallest practicable such a compartment is known as a zone. Each zone will have separate numbers, indications at the main fire alarm indicator.

ZONE CONFIGURATION GUIDELINES Maximum Floor Area Of A Zone Should Not Exceed 2000M The search distance , that is the distance that has to be traveled by a searcher within a fire zone in order to determine visually the position of fire (not reach the fire ) should not exceed 30m A single zone may be extend to several fire compartments If the total floor area of a building is 300m or less then the building need only be one zone regardless the number of floors. If the total floor area of a building is greater then 300m then each floor shall be a separate zone (or set of zones, if the floor area is large enough) There are however two exception for this rules that is: 1. If Communication between two adjacent vertical compartments is at the lowest level, only then can each vertical compartment still be considered to be separate multi storied zones 2.Structures such as stairwell extending to more than one floor but remaining within the same vertical compartment still be considered separate multi stories zone. For multi occupancy building, zone boundaries should not cross occupancy boundaries hence a zone should contain only one occupancy. This ruling may be relaxed for Type M system.

Zone Safeguards Fault occurring at one zone should not effect the operation of another zone. Line/zone isolating device for addressable system. A single fault should not remove protection from an area greater than that allowed for a single zone Two fault should not remove protection from an area greater than 10,000 sq meter. Short circuit should be reported by the control panel within 100 second of occurrence and open circuit should be reported within 60 minutes of occurrence

Type Of Alarm Detection System Conventional System -Two state Detector (Normal state , alarm state) -Two wire connection -Separate indicator In the Main Fire Alarm Panel. -Smoke detector to comply BS 5445 Pt 7 Heat Detector must comply BS 5445 PT 5 1977- Respond 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

Type Of Alarm Detection System Addressable System Addressable detector , call points,signals which is individually identified by the control panel Addressable detectors shall be connected via two wire connection such that the connection of the both wire to form a loop in order to provide circuit integrity. Main difference between the conventional system is that the base of the addressable detector is addressed through soft addressing or dip switch. Multiplex communication technique allow each detector to independently signals it status back to the control panel. Addressable system can also handle output device on the zone circuit, where the address massage can be command instruction to an output device ( on/Off ) Example : Sounder Module , Switching On/Off Relays Interface Module is a device that is used interface the conventional alarm system and the addressable system.

Type Of Alarm Detection System Analog Addressable System The sensors gives an analog output signal representing the value of the sense phenomenon. The output of an analogue addressable detector is variable and it is proportional representation of the sense effect of fire , smoke and flame. Transition of this output from a detector is usually in a form of analog current to the control panel that tells the panel what condition of the room being sense /monitored. Three basic condition to be interpreted by the Control 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 sec).

Types Of Detectors 1. Ion Chamber Smoke Detector1 Response quickly to small smoke particles however its respond slower to dense smoke.  Mechanism :  The detector contains small radioactive source which ionizes the air within the sampling chamber. Thus small current established and set up the potential difference between the collector electrode and the outer cover.. The magnitude of potential increment is used to indicate the smoke density. Exceeding the preset level will trigger the alarm.   2. Photo Electric Scatter Smoke Detector Response quickly to large smoke particles but they have the tendency to ignore the small particles. Mechanism: The unit comprise of an optical system that contains an emitter and a sensor that have lens. The emitter produce a beam of light that was prevented from reaching the sensor by a baffle. However when smoke entering the chamber the light tend to be scattered and apportion of light rays will eventually hit the sensor. The rate of light heating the sensor is proportional to the smoke density. At per determined threshold the output of the sensor signals an alarm to the Main Controller Panel.

Types Of Detectors 3. High Performance Smoke Detector   It responses to the some in the same way as the Photo Electric detector, but there is a rapid rate of rise in temperature will be also taken into considerations which in turn increase their sensitivity accordingly. Therefore this unit can also pick up a very small smoke particles as per ionization Chamber type detector.

Types Of Detectors Heat Detector.   Less sensitive alternative, to be use at the location where the smoke detector cannot be use. To be use for monitoring product that will emit little smoke when burns.  Types of Heat Detector.  1. Rate Of Rise Detectors React to abnormal high rise of change of temperature and provide fastest response over wide range Of ambient temperature. Suitable to be use where large change of ambient temperature will signals the alarm condition to control panel. 2. Fixed Temperature Static Heat Detector. Similar to rate of rise detector but it react to a fix predetermined temperature rather than rate of Rise temperature. Suitable for the use in an area where sudden large change in temperature is considered normal such as kitchen and boiler room. Line type detectors Not Commonly use , it comes in a log wire or tube and are design to sense the condition vicinity to the line. Suitable for cable tunnel, subways duct, aircraft hangers. 

Types Of Detectors 4. Flame Detector Detect electromagnetic radiation from a flame (short wavelength 5 ~ 30 Hz ) The detector cannot respond to fire outbreak until there is a flame. It is practical to use smoke detector in conjunction of flame detector. Often used at the large open areas. A direct line of sight is required for effective detection. It response quickly to a clean burning fuels such as methane, alcohol that cannot be detected by smoke detector.

Types Of Detectors Optical Beam Detector   Optical Beam Detector The detector consist of two gadget Transmitter – Infrared light beam projection Receiver – Received the projected infra red beam. Continuously monitor the received beam. Specifically design for interior uses in large open type area such as warehouse , galleries, manufacturing plant workshop and etc. Where the installation of point type detectors are impossible, difficult. Should be any fire outbreaks, smoke particles rising upwards Interrupts or partly deflect the light beam thus reducing the strength of beam received. If the reduction of signal received by the receiver in the range of 40% to 90% for a period greater than five second it cause the system go to alarm. For optimum /correct operation the transmitter and the receiver must be installed in the roof space or just below the ceiling. Each detector is capable of protecting an area of 7 m each side of beam center line for a distance up to 100 m

Types Of Detectors 6. Aspirating Detector   The detection system includes a small pump that draws air sample from the room air through sets of tubes into a detector element. The tube can be split into several smaller tubes (each drawing air from different location) Due to dilution of smoke the detector element is 100 times more sensitive than the conventional point type. The sucked air is filtered to avoid false analysis from room dust.

Types Of Detectors 7. Duct Probe Unit.   The detector is use to sense the presence of smoke/ combustion product in ventilation duct. Design to operate via principle of differential air pressure. Consist of 2 probe of different length, works on the differential air pressure created between the two probes that are inserted into the duct airflow. The longer probe which is the inlet port for sampling air will lead the samples passing through the sampling chamber for analysis and let the air goes by through the shorter tube.

Detector Coverage 1.Spacing Under Flat Ceiling   Smoke Detector : Every point should lie a horizontal distance of 7.5 m Heat Detector : Every point should lie a horizontal distance of 5.3m

Detector Coverage 2. Spacing Under Pitch Ceiling   If the difference in height between any apex and an 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. For detector mounted on the apex the radius of cover of a detector can be increase by 1% over each degree of slope, up to a maximum 25 % . The increment of coverage area up tp 25% is only applying to detectors mounted on the apex row. For hemispherical dome or a semi cylindrical arch radius of cover of a detector in the center can be taken as 8.93 m for smoke and 6.31 for heat detector.

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

Detector Coverage Obstruction   If the passage of smoke or hot gas is likely to be obstruct by ceiling obstruction such as beam which has depth greater than 150 mm but less than 10 % of the height of the ceiling then the normal coverage distance allowed for the smoke and heat detector should be decrease by twice the depth of the obstruction Smoke Detector Coverage Area : 7.5 m – ( 2 x obstruction depth) Heat detector Coverage Area : 5.3 m – (2 x obstruction depth) Wall and ceiling reaching within 300 mm off the ceiling or obstruction such as beam that is deeper than 10% of the ceiling to floor height shall be treated as separate rooms.

Detector Coverage Ceiling Height.   Detector should not be mounted higher than general limits in table 6 below however the Rapid attendance limit shall be accepted under below mention condition 1.     1. In the event of fire, alarm is automatically sent to the fire brigade service and their usual attendance is 5 minutes or less. 2.      2. There are small section of the ceiling which do not exceed 10% of total ceiling area.

Detector Coverage Wall and Partition   Detector should not be mounted within 500 mm of any wall due to dead spot near wall. Void. Ceiling and Under Voids 800 mm or more in height should also be zoned and protected by detectors. Void less the 800 mm need not to be protected. Unless extensive spread of fire or its product , particularly between rooms and compartments can take place within it before detection.

Detector Coverage Ventilation Effect   Movement of air can cause dilution of smoke /heat intensity until detectors install cant detect the fire outbreak . Smoke test to be conducted to find the most effective location of mounting detectors. 2. Use infrared beam type detectors if suitable. Detectors should not be mount directly in the fresh air input from air conditioning system. Generally spacing of detectors not less than 1 m from the air intake should be maintained. 4. Use duct probe sensor.

Detector Coverage Manual Break Glass Call Points   1.                    Comply with 30 m distance rule. 2.                    Use the same method of operation through out the building. 3.                    Should be located at the exit routs such as floor landing stairways and exit to the open air. 4.                    The time between operation and the sounding of the alarm should ideally les than one second. 5.                    Be mounted at the height of 1.4m from the floor 6.                    Be mounted against contrasting background. 7.                    Manual call points to be indicated separately from detectors.

Audibility requirement of Alarm Sounders Life Protection Requirement.   Where premises are occupied guidelines for alerting the occupant of the building in the event of fire are as follows 1.      1. The sounder should be located near the control panel. 2.            2. In normal surrounding the sound level should be at least 65 dBA or 5 dBA above ambient. 3.            3. If sleeping person are to be woken up , the sound level should be at least 75dBA measured at the bed head. 4.            4. Alarm sound should be the same for all parts of the buildings 5.            5. Frequency of sounders should be between 500 hz to 1000 hz 6.            6. Visual alarm signal such as flashing beacon , etc should be provided in areas of high background noise where some occupants may have impaired hearing. 7.            7. Voice evacuation is an alternative to alarm sounder or bell is permitted.

Audibility requirement of Alarm Sounders Controller Equipments   The sitting of MFP should be in the location of low fire risk Its indication should be quickly available to staff and those who might have to carry out actions in the event of fire Indicator should be easily visible both in darkness and sunlight. If some ambient lighting is required it should be provided either by building emergency lighting supply or by special luminaries fed from the fire alarm system supply. Noise or other sound level in the vicinity of MFP should not mask out the audible alarm of sounder located near the control equipments In multi occupancy building, sitting should be agreed with the other occupants. Mimic diagram should be located along side the control panel Operation of fire alarm panel to be operated by authorized personnel only.

Power Supplies Independent Power From Mains, Standby Batteries with automatic charger Battery life expectancy min of 4 years Batteries capacity shall be able to support running ampere of 24 hr supervisory load and 30 min alarm mode.

Battery calculation If the premise is unoccupied from 6.00 p.m on Friday to 8.00 a.m on Monday. Given that the operating current of the system is 350 mA and the alarm running current is 2.0A Find the total capacity of suitable batteries. Formula: Total Capacity req= ((Max Unsupervised Time+ 24 HR) X Operating Current)+( Alarm Current x Alarm Duration)