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Introduction When is a Fire Alarm System Required
The Fire Precautions Act 1971 & Fire Precautions (Workplace) Regulations 1997Page 3-4 Consultation Types of Fire Alarm Systems Conventional Fire Alarm Systems Removal of Detectors while maintaining the Break Glass Operation Addressable Fire Alarm Systems Analogue Fire Alarm Systems Life or Property System Design Coverage of L1, L2, L3, Systems Coverage P1, P2, Manual Only Systems The Survey The Design The Siting of Manual Call Points The Siting of Sounders Choice of Detectors The Siting of Detectors Smoke Detectors Heat Detectors Control Equipment Power Supplies Fire Compartments Zoning Recommended Cable Types Volt Drop in Cables Routine Testing of the System Close of Document / Contact details Page 5 Page 6 Page 6 Page 7 Page 8 Page 8 Page 9 Page 9 Page 10 Page 11 Page 11 Page 12 Page 12 Page 13 Page 14 Page 15 Page15 - 16 Page 17 Page 18 Page 18 Page 19 Page 19 Page20 - 21 Page22 - 23 Page 24 Page 25
REF: &MARKET018 Issue 2 Date:17/3/98
Introduction The following Guide is based on BS5839 Part 1 on the design and installation of Fire Alarm Systems for general applications. It is intended as a reference only, and not a replacement for BS5839 part 1. When is a Fire Alarm System Required ? There are various statutory documents covering the need for fire protection in various types of premises. The principle documents are: Health and Safety at Work Act 1974 Fire Certificates (Special Premises) regulations 1976 Factories Act 1971 Offices, Shops and Railway Premises Act 1963 Private Places of Entertainment Act 1967 Fire Precautions (Workplace) Regulations 1997
The Fire Precautions Act 1971 Under this Act, all shops irrespective of staff numbers and contents must have: Adequate means of escape while an employee is in the premises (unlocked doors and unobstructed access to them) Appropriate means for fighting fire provided and maintained A Fire Certificate must be obtained from the Fire Authority for premises in which: More than 20 persons are employed at any one time More than 10 persons are employed at any one time other than on the ground floor The shop employees are working in the same building as others and the total in all the premises exceeds 20 or 10 elsewhere other than on the ground floor Highly flammable or explosive materials are stored or used Sleeping Accommodation is provided A Hotel or Boarding House contains sleeping accommodation for 6 or more people, which includes staff and guests, or a Hotel or Boarding House that sleeps a member of staff or any guests above the first floor or below the ground floor.
The majority of Industrial and Commercial premises therefore require a Fire Alarm System with legislation both nationally and locally covering a large proportion of the various types of buildings and their requirements. Automatic Fire Detection will normally be required in premises with: Flammable or Explosive materials are used or stored Where people are sleeping as part of the premises business activity eg: Hotels, Nursing Homes, Hospitals etc When the premises has special evacuation problems eg: disabled and elderly persons, cellars and high buildings All of the above will probably need some degree of Automatic Fire Detection to obtain a Fire Certificate, however with the new Fire Precautions (Workplace) Regulations 1997 it is not always necessary to apply for a certificate. CAUTION - You almost certainly must have a Fire certificate OR must comply to the regulations.
These new regulations came into force on 1st December 1997 and have an important message for those responsible for ownership/management of a property where persons are employed. Unfortunately there are numerous interpretations placed on the regulations and some places are exempted because they are already covered by other legislation or already hold a Fire Certificate.1 To understand the detailed application to your own requirements please contact the following: 1) For advice on Fire Detection and Fire Alarm System Requirements, contact Photain Controls plc For copies of the regulations contact: The Stationary Office Fax:0171 873 8200 Tel:0171 873 9090
The important points to note are as follows: 1 It is now the LEGAL RESPONSIBILITY of EMPLOYERS, PERSONALLY, TO COMPLY WITH THE LEGISLATION, and it will no longer be the responsibility of others, eg: the Fire Service to proscribe to employers the measures to be taken to minimise risk. The Fire Service will, however, continue to provide advice and guidance relating to Fire Precautions. The risk assessment requirements of the 1992 Health and Safety Regulations are extended to include fire risk. Fire precautions are to be based upon the risk assessment. Employers must inform their employees of the results of the risk assessment Employers must provide appropriate means for detecting a fire, raising a fire alarm and for fire fighting. What is considered appropriate will depend upon the size and the nature of the premises, the number of people present and activities undertaken. Current British Standards such as BS5839 Part 1 1988 provide guidance to system design requirements. Employers must provide emergency routes and exits for use in case of fire. These must be kept clear, be available in an emergency and be provided with emergency lighting if requiring illumination. Equipment provided to warn of fire, fight fire and to aid escape from fire must be suitably maintained in good working order. Where fire fighting measures are necessary, employees must be adequately trained and equipped. If employers fail to meet their obligations, the Fire Service has the responsibility for enforcement by means of a series of procedures dependant upon the seriousness of the situation.
If you extend or change a property, you probably need a new or revised certificate
Consultation It is always advisable to consult the Local Fire Prevention Officer at an early stage, regarding the legislation covering a particular premises. The Fire Officer will interpret the Fire Precautions Act or any other act covering a particular premises and advise on the particular type of Fire Alarm System that may be required. It must be remembered that the Fire Prevention Officer is concerned with LIFE, his concern for property is secondary. We would advise that you only consult with a Fire Prevention Officer with the client=s consent. When designing a Fire Alarm System, it is important to consult with all other interested parties, for example: The Local Fire Authority The System Installer The Health and Safety Officer Any Consultant or Architect The Insurance Company During early discussions it is important to establish the purpose of the Fire Alarm System, ie: A) To enhance the safety of the occupants B) To minimise damage to the property Whilst Insurance Companies give good discounts to clients who fit sprinkler systems the fitting of complex Fire Detection Systems seldom lead to a reduction in premiums sufficient to encourage a client to fit a Fire Alarm System for property protection. The vast bulk of Fire Alarm Systems fitted are normally for the protection of Life.
Types of Fire Alarm Systems All Fire Alarm Systems essentially operate on the same principle. If a detector detects smoke or heat, or someone operates a break glass unit, then alarm sounders operate to warn others in the building that there may be a fire and to evacuate. For the system protecting property, it is additionally likely that the Fire Alarm will incorporate remote signalling equipment which would alert the fire brigade via a central station. Wired Fire Alarm Systems can be broken down into three categories, Conventional, Addressable and Analogue Addressable. Conventional Fire Alarm System In a Conventional Fire Alarm System, a number of call points or a number of call points and detectors are wired to the Fire Alarm Control Panel in Zones. A Zone is a circuit and typically one would wire a circuit per floor or fire compartment. The Fire Alarm Control Panel would have a number of Zone Lamps. The reason for having Zones is to give a rough idea as to where a fire has occurred. The accuracy of knowing where a fire has started is controlled by the number of Zones a Control Panel has, and consequently, the number of circuits that have been wired within the building. The Control Panel would then be wired to a minimum of two sounder circuits which could contain bells, electronic sounders or other audible devices. Sounder Circuits and Detection Zones are wired in a star configuration. Each circuit would have an end of line device which is used for monitoring purposes. Photain Controls currently use 20K resistors for use on the end of all sounder circuits and HRMODULES for use on the end of the Detection Circuits for all of their Conventional Control Panels except the PCS800HR Panel and PCS1200HR range which uses a 4K7 resistor.
Removal of Detectors while maintaining the Break Glass Operation BS5939 part 1 1988 (6.6.2) - amendment 6317 January 1991, requires that : AWhere Detectors are designed to be removed from the circuit, removal of any detector from the circuit should not affect the operation of any manual call point.@ On Conventional Fire Alarm Systems one of the following three methods of wiring could be used to meet the Head Removal requirements:
All Manual Call Points and Smoke Detectors could be wired to the same Zone providing all manual Call Points are wired in front of all the automatic detectors.2
An active end of line module (HRMODULE) could be wired to the end of the Zone/s in place of the normal end of line unit. This would allow for the wiring of Call Points and Automatic Detectors in any combination on a circuit zone. If any Detector head is removed from its base then all call points will continue to be operative
It should be noted that with Addressable and Analogue Addressable Fire Alarm Systems the method of wiring to a detector base is different to the method of wiring to a Conventional Base. In addition the method of operation of Addressable and Analogue Addressable Systems means that the requirements of the amendment 6317 (as detailed on the previous page) are always complied with, irrespective of the sequence in which the devices are connected.
With wiring type 1 and 2 as detailed above, the amount of cable required will most probably be increased and will raise the cost of the installation. In addition if the first detector unit is removed then none of the following devices would be operative. This restriction would not apply to Type 3 as detailed
Addressable Systems The detection principle of an Addressable System is similar to a Conventional System except that the Control Panel can determine exactly which detector or call point has initiated the alarm. The detection circuit is wired as a loop and up to 99 devices may be connected to each loop. The detectors are essentially Conventional Detectors, with an address built in. The address in each detector, is set by dil switches and the Control Panel is programmed to display the information required when that particular detector is operated. Additional Field Devices are available which may be wired to the loop for detection only ie: it is possible to detect a normally open contact closing such as sprinkler flow switch, or a normally closed contact opening. Sounders are wired in a minimum of two sounder circuits exactly as a Conventional System. Loop Isolation Modules are available for fitting on to the detection loop/loops such that the loop is Asectioned@ in order to ensure that a short circuit, or one fault will only cause the loss of a minimal part of the system.3 Analogue Fire Alarm Systems Analogue Fire Alarm Systems are often known as Intelligent Fire Alarm Systems. There are several different types of Analogue Systems available which are determined by the type of protocol which they use. The bulk of Analogue Detectors available are Afairly stupid@ as the Detectors can only give output signals representing the value of sensed phenomena. It is left up to the Control Unit to decide whether there is a fire, fault, pre alarm or whatever. With the Photain True Intelligent Analogue System each detector effectively incorporates it=s own computer which evaluates the environment around it, and communicates to the Control Panel whether there is a fire, fault or the detector head needs cleaning. Essentially however, Analogue Systems are far more complex and incorporate far more facilities than Conventional or Addressable Systems. Their primary purpose is to help prevent the occurrence of false alarms. With the Photain Analogue Addressable System up to 127 input devices ie: Smoke Detectors, Call Points, Heat Detectors, Contact Monitors and other interface devices may be wired to each detection loop. In addition to the 127 Input Devices, up to 32 Output Devices such as Loop Sounders, Relay Modules and Sounder Modules may also be connected. Photain Analogue Systems are available in 2,4 and 8 loop versions which means large premises can be monitored from one single panel. Isolator units should be connected between Asections@ of detectors as described for Addressable Systems.
3 BS5839 Part 1 Section 7.2 dictates this loss to be a maximum of 2000 square metres of area protected -See section 7 on pages 11 - 12 of BS5839 for further details
Life or Property BS5839 Part 1, classifies systems and divides them into six different types: L1 L2 Intended for life safety and covering the whole building Intended for life safety and covering escape routes and other areas of high risk Protecting only the escape routes Intended for property protection and covering the entire building Intended for property protection covering any potentially high risk areas Intended for giving the alarm in response to operation of a manual call point and having no means of automatic detection
L3 P1 P2 M
System Design Before staring the design you will need to ensure that certain information is available. This may be given in the specification or it may have to be obtained by consultation. As well as the purchaser, there may be a requirement to consult with other interested parties. The most important of which will probably be the Fire Prevention Officer of the local Fire Brigade. The information which should be available includes: A The type of system required ie: L1, L2, L3 etc and where appropriate, parts of the premises to be covered. The action to be taken in the event of fire Whether other occupants of a multi occupancy building will be affected Whether other work is to be done at the same time. If so then consultation with other contractors may be required. A Method of calling the Fire Brigade Whether the type of occupants or activity in the building will require a greater provision of Manual Call Points than normal A likely attendance time of the Fire Brigade
Coverage L1 Systems In an L1 System, all areas of the building should be covered. It is normal not to cover the following areas: Lavatories and Water Closets unless they contain electric hand dryers Voids less than 800mm in height Coverage L2 Systems Coverage of L2 systems depends on the vulnerability of the likely occupants and the probability of ignition of fires, ie: Sleeping Areas without supervision Areas having a high probability of ignition ie: day accommodation, store rooms, kitchens and plant rooms Where occupants are especially vulnerable due to illness, age or are unfamiliar with the building. It should be noted that L2 systems always include L3 coverage. Coverage L3 Systems In L3 systems, coverage should be provided for escape routes and any areas in which the occurrence of a fire would directly threaten escape routes. The following areas should therefore be covered: Corridors, passages and circulation areas Stairwells The top of vertical risers At each level within 1.5m of an access point to a lift shaft or other vertical riser In all rooms opening onto an escape route
Coverage P1 Systems In a P1 system all areas of the building should be covered with the exception of: Lavatories and Water Closets Voids less than 800mm in height and such that extensive spread of fire or fire products cannot take place in them prior to detection by detectors outside the void Coverage P2 Systems P2 systems give coverage of only part of the building. The areas covered would normally have a high fire risk and unprotected areas should be separated by fire resisting construction. Both P1 and P2 systems would invariably be connected to the Fire Brigade via a central station. It would be on an extremely irregular basis that you would ever be requested to fit a P type of system. Manual only Systems An AM@ system provides for Manual only alarm and systems intended for multi occupancy buildings are given the suffix AX@. The Survey If you are surveying a building we would suggest you start at the top of the building and work down. Two basic reasons for this are as follows: A If you are as athletic as the writer of this guide then you can ride the elevator to the top floor and the rest of the survey is downhill! If you start at the top of the building then you can be sure to check the top of each stairwell. This will need a detector (except a Manual only System) even on an L3 System. As you work your way down the building you can then check how often detectors are required vertically down the stairwell. On Type L Systems, BS5839 states that this shall be at vertical intervals not exceeding 10.5 metres which normally works out to be every third floor. On Type P Systems, there should be detectors on every main landing.
REF: &MARKET018 Issue 2 Date: 17/3/98
If you are designing onto a set of drawings then we would recommend that you adopt the following procedure. 1 2 Identify and plan out where all break glass points are required. Note where all the Sounders are required. Indicate where the Control Panel will be. You now have an >M= System. Consider fitting door holders/closers onto doors which might otherwise get propped open. Doors leading onto stairwells should not be fitted with Door Holders. There was an old GLC regulation which requires a Smoke Detector to be fitted within 2m either side of the door or pair of doors fitted with a Door Holder/s - Closer/s and many authorities ie: West Sussex still require this. Mark down where all detectors are required in escape routes, top of stairs, landings, ceilings at vertical intervals not exceeding 10.5m, top of vertical risers, within 1.5m of access to lift shafts and within rooms opening onto escape routes. You should now effectively have the design of an L3 System and can now go on to add detectors to bring the system up to L2 or L1 as required. Indicate the number of Zones that will be required.
Siting of Manual Call Points A Break Glass Call Point is a device which enables personnel to raise the alarm by breaking the frangible element on the facia. They should be mounted 1.4m from the floor and sited where they can be easily seen. Manual Call Points should be sited on the floor landings4 of stairways and at exits to open air. It should be noted that many Fire Officers prefer Call Points to be fitted on the floor side of an access door to a staircase so the floor of origin is indicated at the Control Panel. Where necessary, extra points should be sited5 so that the greatest travel distance from any point in the building to the nearest call point does not exceed 30m. A greater number of Call Points may be needed in high risk areas or if the occupants are likely to be slow in movement.
This is a British Standards Requirement Preferably on Exit Routes
Siting of Sounders An Alarm Sounder may be a bell or electronic sounder and it must be audible throughout the building. A minimum sound level of either 65db(A) or 5db(A) above any background noise likely to persist for longer than 30 seconds, which ever is the greater, should be produced by the sounders at any point in the building. It is unlikely that more than 65DB will be available if the sound has to carry through more than one door. If the alarm system is used in premises such as hotels, boarding houses etc where the alarm is intended to wake sleeping persons then the sound level at the bedhead should be at least 75db(A) with all doors closed. We would strongly recommend that you allow one sounder per bedroom. A few bells sprinkled down the corridor in hotel will not produce 75db(A) at all the bedheads. It is important to note that the above audibility levels must be produced with all doors shut, after the works on site have been completed. If a Fire Officer even expects that there is a lack of audible sounders, then he is sure to check each area with a db metre and prove it. It can be costly and very inconvenient to have to return to site and fit additional sounders. A minimum of two sounder circuits should be wired and a larger number of quieter sounders are preferable to a small number of very loud sounders. At least one sounder should be installed in each fire compartment and all sounders throughout an installation must produce a similar sound, ie: you cannot mix an electronic sounder and bells.
REF: &MARKET018 Issue 2 Date17/3/98
Choice of Detectors Smoke Detectors will generally detect a fire far sooner than heat detectors. It is therefore preferable to fit Smoke Detectors unless there is any possibility of false or unwanted alarms. It is not advisable for example to fit a Smoke Detector in a kitchen as anybody burning toast would cause an unwanted alarm. Heat Detectors should be fitted in boiler rooms, generator rooms, garages and dusty areas. The products of combustion produced by a boiler, a leaky exhaust on a generator or exhaust fumes from a vehicle could all cause a smoke detector to operate and produce an unwanted alarm. Fixed Temperature Heat Detectors should be installed in areas where one would normally expect a sudden rise in temperature for instance kitchens and boiler rooms. Rate of Rise Heat Detectors should be installed where Smoke Detectors would be unsuitable but one would not expect a sudden rise in temperature for instance, garages, car parks, dusty workshops etc. There are two basic types of Point Smoke Detectors: 1 Ionisation chamber Smoke Detectors which are very sensitive to smoke with small particles ie: fresh cellulosic smoke and the source of almost invisible smoke one gets with burning paper and spirit. They are relatively insensitive to smoke with large particles for example, smoke produced by burning plastics or stale smoke. Optical Smoke Detectors are sensitive to optically dense smoke ie: smoke with large particles and they are relatively insensitive to optically thin smoke.
Some countries ie: Italy, Japan, Qatar only use Optical Smoke Detectors and within parts of the Middle and Far East, only Ionisation Detectors are used. Within the UK systems can comprise of a mixture of the two. The demise of most people is caused by thick dense choking smoke which is normally a greater problem than getting burnt. For this reason Optical Detectors are normally used on escape routes such as corridors and stairwells. Ionisation Smoke Detectors are normally fitted within office and other general areas.
Siting of Detectors In a building the greatest concentration of Smoke and Heat will generally collect at the highest parts of the enclosed areas and it is here therefore, that the detectors should normally be sited. Smoke Detectors Smoke Detectors should be sited so that the sensing element is not less than 25mm, nor more than 600mm below the ceiling or roof. If a protected space has a pitched or northern light roof, then Smoke Detectors should be installed in each apex. The maximum horizontal distance between any point in the area being protected and the nearest detector should be as follows: Under flat horizontal ceilings and corridors more than 5m wide, then the maximum distance for Point Type Smoke Detectors should not exceed 7.5m. The maximum area of coverage of a Point Smoke Detector is 100 square metres. On the rear of all Photain Smoke Detector Data Sheets, a diagram showing the relevant coverage they provide is shown. In corridors the number of detectors required depends on the corridor width. When installing Smoke Detectors the following data can be used: Corridor Width (m) 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.0 or more Allowable Radius of Cover (m) 9.4 9.2 9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.5 Maximum Spacing between Detectors (m) 18.76 18.33 17.89 17.44 16.97 16.49 16.00 15.49 14.97 14.42
The maximum height that smoke detectors should be installed at is as follows: Point Smoke Detectors Optical Beam Smoke Detectors
REF: &MARKET018 Issue 2 Date:9/3/98
10.5m 25m
If detectors are to be fitted in the apex of a pitched or north light roof then a row of detectors should be sited within the apex. One row of detectors should be sited at the highest point a minimum distance of 0.5m from the vertical wall. Add to the maximum horizontal distance 1% for each degree of the slope up to a maximum of 25%. For instance a point type detector at the apex of a 20 degree slope would work out as follows: 20% of 7.5m = 1.5m. Therefore the maximum distance between detectors = 7.5 + 1.5 = 9m. The maximum area of coverage may also be increased proportionally. Where the passage of Smoke or Hot Gases from a position to a detector is likely to be disturbed by a ceiling obstruction such as a beam having a depth greater than 150mm but less than 10% of the height of the ceiling, then the horizontal distance should be decreased by twice the depth of the obstruction. For instance for a Point Type Smoke Detector obstructed by a 200mm depth beam then the maximum distance between detectors = 0.2m x 2 = 0.4m. 7.5m - 0.4m = 7.1m. Where a ceiling obstruction, such as a beam is greater than 10% of the height of the ceiling then the area either side of the obstruction should be considered as separate rooms. Ceiling beams less then 150mm in depth can be ignored. Optical beam smoke detectors are useful for covering large unobstructed roof areas such as those found in most warehouses. They can be quite cost effective as one smoke beam can provide the coverage of many individual point detectors. A smoke beam typically comprises of a Projector, a Receiver, a Remote Manual Reset Unit and a Local Power Supply with battery standby. Optical Beam Smoke Detectors should be mounted as follows: (m = Metres) • • • • • • • The minimum height above floor level Maximum height above floor level Minimum Optical Beam length Maximum Optical Beam length Minimum distance of Optical Beam From a flat ceiling or apex Maximum horizontal distance between Optical = Beams measured at right angles to a Beam The Maximum horizontal distance between Optical Beam and an adjacent wall or partition = = = 2.7m = 10m 100m = 0.3m 25m
Heat Detectors Heat Detectors should be sited so that the heat sensitive element is not less than 25mm, nor more than 150mm below the ceiling or the roof. The maximum horizontal distance between any point in the area being protected and the nearest detector should be as follows: Under flat horizontal ceilings and corridors more than 5m wide then the maximum distance between any heat detector and any wall or partition should be 5.3m. The maximum area of coverage per heat detector is 50 square metres. On the rear of all Photain Heat Detector Data Sheets, a diagram showing the relevant coverage they provide is shown. There is also information regarding detector coverage in corridors using Heat Detectors. As Heat Detectors are very seldom used in corridors then please consult British Standard BS5839 Part 1, should you require this information. The maximum height that Heat Detectors should be installed at are as follows: Grade 1 Heat Detector Grade 2 Heat Detector Grade 3 Heat Detector High Temperature Heat Detectors 9m 7.5m 6m 6m
Control Equipment The Fire Alarm Control Equipment should normally be sited in an area as follows: Preferably in an area of low fire risk and on the ground floor by the entrance used by the Fire Brigade and preferably viewable from outside of the building. It should be located in an area common to all building users and where automatic detection is in use, the Control Panel should be in a protected area. An alarm sounder should be sited next to the Control Unit, but not too near the telephone position. A suitable zone chart of the building should normally be installed adjacent to the Control Panel. Power Supplies Two power supplies are required ie: mains and battery and these are normally built into the Fire Alarm Control Panel. Standby batteries must allow the system to operate without mains for 24 hours longer than the building is likely to be unoccupied and then support the sounders for an additional half hour. If the mains supply is supported by an emergency generator then six hours standby plus half an hour alarm load is sufficient. All modern Fire Alarm Systems are 24 volts. On the medium and larger sized Fire Alarm Systems, the standby batteries will often not fit within the Control Panel. Where standby batteries are contained within a separate housing, then this housing must be as close as possible to the main Fire Alarm Control Panel. If the power supply or battery housing is located more than 10 metres from the main Fire Alarm Control Panel then serious volt drop problems can arise. Standby batteries are invariably of the sealed lead acid variety. Use of nickel Cadmium Batteries is not cost effective and automotive batteries must not be fitted.
Fire Compartments Buildings are normally split into fire compartments with each compartment so constructed as to prevent the spread of fire from one compartment to another. Each floor and each stairwell within a building is normally a separate fire compartment. Within a small factory, the factory unit will normally be separated from the offices by >firewalls= to prevent the spread of smoke and fire from one to the other. The factory and offices will therefore be in separate fire compartments. A zone should normally only cover a single fire compartment. Zoning If the total floor area (ie: the total of the floor areas of each floor of the building) is not greater than 300 square metres then the building need only be one zone, no matter how many floors it has. In general, if the total floor area is greater than 300 square metres, then each floor should be a separate zone (or set of zones, if the floor is big enough). There are two exceptions: A If the building is sub divided into fire compartments, then any compartment communicating with other compartments only at the lowest level of the building can be treated as if it were a separate building ie: if a floor area is not greater than 300 square metres then it can all be one zone, irrespective of the number of storeys. Where stairwells or similar structures extend beyond one floor, but are in one fire compartment, the stairwell should be a separate zone.
There are two restrictions on the maximum size of a zone, irrespective of the size of the building A B Its total Floor area should not exceed 2000 square metres The search distance should not exceed 30 metres. This means that a searcher entering the zone by the normal route should not have to travel more than 30 metres after entering the zone in order to see a fire big enough to operate a detector, even if the fire is only visible from the extreme end of his search path. Remote indicators show an alarm in a closed area and their fitting can enable larger areas to comply to the search distance requirements.
There are two restrictions on the configuration of a zone, irrespective of its size. A If the zone covers more than one fire compartment, then the zone boundaries should follow compartment boundaries If the building is spilt into several occupancies, then each occupancy should lie within a separate zone (or set of zones), no zone should be split between two occupancies
Recommended Cable Types All cables used in Fire Alarms must have a minimum conductor size of 1.0mm squared. BS5839 Part 1, recommends 11 types of cable which may be used on a Fire Alarm System where prolonged operation in a fire is not required. Therefore 1.0mm twin and earth cable for instance, may be used on detection circuits of Conventional Fire Alarm Systems and the detection loops of Addressable and Analogue Systems providing sounders are not connected to them. Only two types of cable may be used on Fire Alarm Circuits where prolonged operation in a fire is required. 1 Mineral - insulated copper - sheath cables (MICC) complying with BS6207 AND 2 Cables complying with BS6387, and meeting at least the requirements of categories AWX or SWX
In other words, on sounder circuits and for wiring between a power supply and or battery housing and the main fire alarm control panel you must use one of the following types of cable. MICC, Flamsil, Firetuff or similar On Addressable and Analogue Addressable Fire Alarm Systems we would recommend the use of a screened cable such as BICC Flamsil or Firetuff or MICC for all wiring so as to minimise the possibility of interference being picked up by or being transmitted by the data loops. In the larger buildings within the London area (old section 20 buildings) only bare MICC cable is often specified. In summary therefore MICC cable used for all your fire alarm wiring would be acceptable anywhere. However, ordinary twin and earth 1.0mm cable may be used on detection circuits of Conventional Systems in certain circumstances. As far as possible, joints should be avoided except where a joint is inside one of the systems components ie: Control Panel, detector, Call Point, Sounder etc. Where joints are required elsewhere they should be enclosed in a suitable junction box marked fire alarm to ensure that the fire alarm systems is not accidentally interfered with.
Fire Alarm Cables, should always be segregated from cables for other systems. The segregation of MICC cables with a plastic sheath is of course not so critical as the segregation of ordinary twin and earth cable. Installation of cables should be in accordance with good practices recommended in the latest edition of the IEE wiring regulations Connection to the mains supply should be via an isolating switch fuse reserved solely for the purpose. Its cover must be painted red and labelled AFire Alarm - do not switch off@. Conductor size should take voltage drop into account. In any case conductors should have a cross sectional area of not less than 1 square millimetre. Where possible cables should be routed through areas of low fire risk. Cables installed in damp, corrosive or underground locations should be PVC sheathed and where there is a risk of mechanical damage should be protected accordingly. If Cables are installed less than 2.25m above the floor should they normally be protected.
Volt Drop in Cables Unless a detection circuit or detector loop exceeds 1 kilometre in length, it is unlikely to give rise to a concern about volt drop. If there are fairly long sounder circuits or a sounder circuit has a large number of Sounders, Buzzers, Voice Alarms or Flashing Beacons etc on it, then voltage drops can cause problems. Providing the overall volt drop does not exceed 4 volts on sounder circuits then the system should operate satisfactorily. The calculation of the precise voltage drop at each point in the system is a long and tedious calculation and way beyond the scope of this guide. However, to get a rough idea as to whether a system will operate satisfactorily one can use the following calculations. To start with we need to know approximate volt drop characteristic of different sizes of cable 1.0mm cable 1.5mm cable 2.5mm cable 4.0mm cable 6.0mm cable If one is using 1.0mm cable: Multiply 42 by the length of the cable in metres Multiply this by the current of all the devices on the length of the cable Divide the entire figure by 1000 This gives a rough idea of the voltage drop. Lets take an example where you have 30 Sounders, each with a current consumption of 20mA on 200 metres of 1.0mm cable. If you were to wire in 1.0mm cable then the calculations would look something like this: 42 x 200 metres x 30 sounders x 0.02 amps 1000 The answer is 5.04 volts. This is more than the 4 volts previously discussed and therefore we would suggest that 1.0mm cable would be unsuitable in this instance. Lets now try the calculation using 2.5mm cable. In this instance we have the following: 17 x 200 metres x 30 sounders x 0.02amps 1000 The answer is 2.04 volts. A two volt drop is of course acceptable. = = = = = 42mV per amp per metre 28mV per amp per metre 17mV per amp per metre 10mV per amp per metre 7mV per amp per metre
Should you be on a budget and be considering using 1.5mm cable, the answer after making the calculation would be 3.36 volts and this is indeed acceptable. However do not disclaim the possibility that at a later date you may wish to add extra sounders, and therefore you would be pushing the system to its full limitations by utilising the 1.5mm cable. You may encounter examples where even 2.5mm cable is not sufficient. Rather than use a larger cable which would be extremely difficult to terminate in the rear of most sounders, it is usually better to run additional sounder circuits and spread the load. Should you be using a remote power supply or battery housing to power the control panel, then the voltage drop becomes very significant. As well as the consumption of the Control Panel, one must consider the operating load of the sounders. It is particularly important to keep voltage drop as low as possible and preferably below 1 volt or power levels will decrease even before you have commenced consideration regarding the calculation of the volt drop to the sounders from the control panel. An example of this now follows. We have a control panel which consumes 260ma and has a number of sounders connected, which in total use 3amps in the alarm condition. If you wired between the remote power supply and the control panel which was only 20 metres away in 1.0mm cable then the calculation would be as follows: 42 x 20 metres x 3.26 amps = 2.7 volt drop 1000 This would clearly be unacceptable. Should we be able to locate the remote power supply within 10 metres of the control panel and wire it in 2.5mm cable the calculations should look as so: 17 x 10 metres x 3.26 amps = just over half a volt 1000 The above example should be acceptable. However when calculating the volt drop on your sounder circuits it would be advisable not to allow any volt drop to exceed 3.5 volts. A word of warning however, the writer of this guide has seen several examples where electricians have installed cable that is too thin on sounder circuits and consequently the system has encountered substantial volt drops ie: in excess of 12. A way around this has then been sought and the 24 volt bells have been substituted with 12 volt bells. This does not work, as if you lower the voltage the current increases and so the problem gets worse.
Routine Testing of the System The system should be regularly tested and serviced and BS5839 Part 1 makes the following recommendations: DAILY Check that the panel indicates normal operation. If not record any fault indicated in the event log and report the fault to a responsible person. Check that any fault recorded from the previous day has received attention. Operate a manual call point or smoke detector to ensure the system operates properly. Each week a different detector or call point should be checked. Check that the sounders have operated and then reset the system. Check the battery connection. Any defect should be recorded in the log book and reported. Action should be taken to correct the defect. Check entries in the log book and take any necessary action. Examine the batteries and their connections. Operate a manual call point and smoke detector in each zone to ensure that the system operates properly. Check that all sounders are operating. Check that all functions of the alarm control panel operate by simulating fault conditions. Visually check that structural alterations have not been made that could have an effect on the siting of detectors and other trigger devices. Complete the event log with details of the date, time, trigger device tested and >Quarterly Test= in the event section. Any defects or alterations to the equipment should also be entered
ANNUALLY Carry out an inspection as detailed for this quarterly inspection. Every detector should be tested in site. All cable fitting and equipment should be checked to ensure that they are secure and undamaged. A qualified engineer should carry out the quarterly and annual inspections and issue a certificate after each annual inspection. It is normal practice for 1/4 of all detection systems to be cleaned and checked on each quarterly visit so that the entire system has been properly maintained after the fourth visit. Whilst the end user of the fire alarm system may be expected to carry out the daily and weekly functions very few would be adequately equipped or trained to carry out the quarterly and annual tests. Photain Controls plc would be please to submit a price for the maintenance of any Fire Alarm System which has been installed using Photain Fire Alarm Equipment.
The intention of this guide is to keep the information given as simple as possible. This necessitates the omission of much information contained within the various British Standards and the requirement of the various fire acts. Photain Controls can therefore not take any responsibility for the way in which any information contained in this guide is used.
For further information, please contact us: Photain Controls plc Rudford Estate Ford Aerodrome Arundel West Sussex BN18 0BE Tel : 44 (0) 1903 721531 Email : enquiry@photaincontrols.plc.uk Fax : 44 (0) 1903 726795 Web Site : www.photaincontrols.plc.uk
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