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Fire alarm systems

Technology in fire alarm systems is constantly changing, but the goal always remains the same, to protect life and property.

Sense Fire Ltd can offer every type of fire alarm system available. We design, install, commission, certify and maintain all fire alarm systems types. We can supply fire alarm equipment and devices on a wholesale basis, just contact us for more details of what you require.

Fire alarm system design category information

Fire detection and fire alarm systems can be installed in buildings to satisfy one, or both, of two principal objectives, namely protection of life and protection of property. The objectives can differ in time or place. Other possible objectives exist, such as protection against business interruption and protection of the environment; these are likely to be satisfied by the recommendations in this standard for protection of property.

Because of the great variety of applications for systems covered by this part of BS 5839, systems are divided into a number of different Categories, 

Category M systems are manual systems and, therefore, incorporate no automatic fire detectors.

Category L systems are automatic fire detection and fire alarm systems intended for the protection of life. They are further subdivided into:

  1. a) Category L1: systems installed throughout all areas of the building.

The objective of a Category L1 system is to offer the earliest possible warning of fire, so as to achieve the longest available time for escape;

  1. b) Category L2: systems installed only in defined parts of the building.

A Category L2 system ought to include the coverage necessary to satisfy the recommendations of this standard for a Category L3 system; the objective of a Category L2 system is identical to that of a Category L3 system, with the additional objective of affording early warning of fire in specified areas of high fire hazard level and/or high fire risk;

  1. c) Category L3: systems designed to give a warning of fire at an early enough stage to enable all occupants, other than possibly those in the room of fire origin, to escape safely, before the escape routes are impassable owing to the presence of fire, smoke or toxic gases;

NOTE 1 To achieve the above objective it is normally necessary to install detectors in rooms which open onto an escape route (see 8.2).

  1. d) Category L4: systems installed within those parts of the escape routes comprising circulation areas and circulation spaces, such as corridors and stairways. The objective of a Category L4 system is to enhance the safety of occupants by providing warning of smoke within escape routes;

NOTE 2 The installation of detectors in additional areas is not precluded, and the system could then still be regarded as a Category L4 system.

  1. e) Category L5: systems in which the protected area(s) and/or the location of detectors is designed to satisfy a specific fire safety objective (other than that of a Category L1, L2, L3 or L4 system). Often, the design is based on a localized need for fire detection in only part of a building. Protection might be provided to compensate for some departure from normal guidance elsewhere or as a part of the operating system for a fire protection system. Such a system could be as simple as one that incorporates a single automatic fire detector in one room (in which outbreak of fire would create undue risk to occupants, either in the room or elsewhere in the building), but the system could comprise comprehensive detection throughout large areas of a building in which, for example, structural fire resistance is less than that normally specified for buildings of that type.

NOTE 3 The protection afforded by a Category L5 system might, or might not, incorporate that provided by a Category L2, L3 or L4 system.

Category P systems

Category P systems are automatic fire detection and fire alarm systems intended for the protection of property. They are further subdivided into:

a) Category P1: systems installed throughout all areas of the building.

The objective of a Category P1 system is to offer the earliest possible warning of fire so as to minimize the time between ignition and the arrival of firefighters;

  1. b) Category P2: systems installed only in defined parts of the building.

The objective of a Category P2 system is to provide early warning of fire in areas of high fire hazard level, or areas in which the risk to property or business continuity from fire is high.

NOTE The defined parts of the building might be as few as one or more rooms, or as extensive as, for example, complete floors of the building.

Selection of category

Even in buildings with comprehensive fire detection, the provision of manual call points is still normally of great value; people in the vicinity of a fire are normally aware of the fire, and able to raise the alarm by use of a manual call point, before it is detected automatically.

If a system is intended to fulfil the objectives of more than one category of system, then the system needs to conform to the recommendations for each of the categories. For example, a system whose sole purpose is to provide property protection throughout the building (a Category P1 system) might not need to give an alarm signal of sufficient audibility to rouse all occupants who might sleep in the building. If, however, the system were also installed for the purpose of life safety (a Category L system), sufficient fire alarm sounders to rouse sleeping occupants would be necessary.

This part of BS 5839 does not recommend which category of system needs to be installed in any given premises. The various system categories are to be regarded as a “menu”, from which purchasers, users, specifiers, enforcing authorities, insurers or system designers can select a suitable system for any building. However, Annex A provides information on the Categories of systems that are typically installed in various types of premises.

Because of the wide range of systems covered by the recommendations of this part of BS 5839, the specification of requirements for a system, by a purchaser, user, enforcing authority or insurer, or the description of a system by a designer or installer, by reference to this standard, without a reference to system category, has little meaning.

The category of system to be installed always needs to be included in the specification. Similarly, the specification of any category of system, other than Category L1, M or P1, always needs to include details of those areas of the building that are to be protected.

In some cases, there is little distinction between, for example, a Category P1 system with variations

(see Clause 7) and a Category P2 system. In such cases, either description could be used; the designated system category is to be regarded as a shorthand form of description, rather than a rigid form of prescription. Where a choice exists, however, the description needs to be based on the specified objective of the system.

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