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 (manual break point), 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 four categories:

  • Conventional
  • Analogue Addressable
  • Addressable
  • Wireless systems

Types of Fire Alarm Systems

In a Conventional Fire Alarm System, 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 has a number of Zone Lamps. The reason for having Zones is to give a rough idea as to where a fire has occurred. This is important for the fire brigade and of course for the building management. The accuracy of knowing where a fire has started is controlled by the number of Zones a Control Panel has and the number of circuits that have been wired within the building. The Control Panel is wired to a minimum of two sounder circuits which could contain bells, electronic sounders or other audible devices. Each circuit has an end of line device which is used for monitoring purposes.

Analogue Addressable 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 standard Analogue Detectors available are fairly stupid as the Detectors can only give output signals representing the value of detected phenomena. It is left up to the Control Unit to decide whether there is a fire, fault, pre-alarm or other. With a true Intelligent Analogue System each detector effectively incorporates its 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 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 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.

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.

Wireless fire alarm systems are an effective alternative to traditional wired fire alarm systems for all applications. They utilise secure, licence-free radio communications to interconnect the sensors and devices (smoke detectors, call-points, etc.) with the controllers. It is a simple concept, which provides many unique benefits and is a full analogue addressable fire detection system without the need for cable.

System Design

Before starting, At Unite Security & Electrical, 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.

Key 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 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

Inspection and Servicing

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 satisfactorily
  • Each week, a different manual call point should be tested
  • Voice 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 tested
  • Any vented batteries used as a standby power supply for the fire detection and fire alarm system inspected

Inspection and Servicing by a competent person

At Unite Secuirty, we can take over the complete Inspection and services for you, as our engineers are fully trained to complete the following Tasks noted below.

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 necessary
  • Batteries should be checked and tested
  • Control panel functions should be checked and tested
  • Fire alarm devices should be tested
  • Facilities for automatic transmission of alarm signals to an alarm receiving centre (ARC) should be checked after advising the ARC of the proposed actions
  • All fault indicators and circuits should be tested and checked
  • Printers should be tested
  • Other checks and tests recommended by the manufacturer should be carried out
  • Outstanding defects should be reported and the logbook completed and servicing certificate issued.
  • The recommended period between successive inspection and servicing visits should not exceed six months.

Quarterly inspection of vented batteries

  • Vented batteries should be examined by a person with relevant competence and should be topped up if necessary

Inspection and test of a system over a 12 month period

  • The switch mechanism of every manual call point should be tested
  • Every 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 detectors
  • All fire alarm devices (both visual and audible) should be tested
  • Certain filament lamps should be replaced
  • Radio fire detection and fire alarm system signal strengths should be checked
  • Visual inspection of readily accessible cable fixings should be undertaken
  • The cause and effect programme should be checked
  • The standby power supply capacity should be checked
  • Other annual checks and tests recommended by the system component manufacturers should be undertaken
  • Outstanding defects should be reported and the servicing certificate issued.
  • As this is labour-intensive servicing, it is recommended that the work can be spread over two or more service visits during each twelve-month period