Introduction

All Fire Alarm Systems essentially operate on the same principle. If a detector detects smoke or heat, or CO 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. It may also incorporate remote signaling equipment which would alert the fire brigade via a central station.

Fire Alarm Systems can be broken down into three categories, Conventional, Addressable Analogue Addressable and Wireless systems.

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. Each circuit would have an end of line device which is used for monitoring purposes.

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 i.e. 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 sectioned in order to ensure that a short circuit, or one fault will only cause the loss of a minimal part of the system.

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 fairly 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 a 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 Analogue Addressable System up to 127 input devices i.e.: 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. 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 sections of detectors as described for Addressable Systems

Before staring the designer 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

Points to consider
 The type of system required i.e. L1, L2, L3 etc and where appropriate, parts of the premises to be covered. The action to be taken in the event of fireWhether other occupants of a multi occupancy building will be affectedWhether 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 BrigadeWhether the type of occupants or activity in the building will require a greater provision of Manual Call Points than normalA likely attendance time of the Fire Brigade

This information is provided for the general guidance of fire detection and fire alarm system users. As it is a summary, it omits much of the information included in BS5839 part 1. It is therefore not intended to be a replacement for the detailed recommendations included within British Standard.

Routine testing by the user

It is vital for a regular test to be undertaken to ensure that there has not been a major failure of the entire fire detection and fire alarm system that may otherwise go unnoticed.

Weekly tests
Test a manual call point during working hours to cheek that the control panel and alarm sounders operate satisfactorilyEach week, a different manual call point should be testedVoice alarm systems should be tested weekly in accordance with BS5839 Part 8. If the system is connected to an Alarm Receiving Centre (ARC) for calling the fire brigade, it is very important that the ARC is notified before testing commences and when it is complete

Monthly tests
Any automatically started generator used for the fire detection and fire alarm system should be testedAny vented batteries used as a standby power supply for the fire detection and fire alarm system inspectedInspection and Servicing by a competent person

Inspection and Servicing by a competent person

The inspection and servicing should be undertaken by organisations with the appropriate competence.

Periodic inspection and testing The period between visits to undertake inspection and service should he based upon a risk assessment but the maximum period between visits should not exceed six months.The log book should be inspected A visual inspection should be made to check whether structural or occupancy changes have been made that require changes to the fire detection and fire alarm system.False alarm records should be checked and relevant action taken if necessaryBatteries should be checked and testedControl panel functions should be checked and testedFire alarm devices should be testedFacilities for automatic transmission of alarm signals to an alarm receiving centre (ARC) should be checked after advising the ARC of the proposed actionsAll fault indicators and circuits should be tested and checkedPrinters should be testedOther checks and tests recommended by the manufacturer should be carried outOutstanding defects should be reported and the logbook completed and servicing certificate issued.

Quarterly inspection of vented batteries Vented batteries should be examined by a person with relevant competence and should be topped up if necessaryInspection and test of a system over a 12 month period The switch mechanism of every manual call point should be testedEvery automatic fire detector should be examined and functionally tested. This includes, but is not limited to; smoke detectors, resettable heat detectors, optical beam smoke detectors, aspirating fire detection systems, carbon monoxide fire detectors and flame detectorsAll fire alarm devices (both visual and audible) should be testedCertain filament lamps should be replacedRadio fire detection and fire alarm system signal strengths should be checkedVisual inspection of readily accessible cable fixings should be undertakenThe cause and effect programme should be checkedThe standby power supply capacity should be checkedOther annual checks and tests recommended by the system component manufacturers should be undertakenOutstanding defects should be reported and the servicing certificate issued.

Non-routine attention

The arrangements in the above section, inspection and servicing are intended to maintain the system in operation under normal circumstances. However, from time to time, the fire alarm system is likely to require non-routine attention, including special maintenance. Non-routine maintenance includes: special inspection of an existing fire alarm system when a new servicing organization takes overservicing the system;repair of faults or damage;modification to take account of extensions, alterations, changes in occupancy or false alarms;action to address an unacceptable rate of false alarms;inspection and test of the system following a fire.