Factors in design and application of fire detection and alarm systems.
• Principal components of systems.
• Detection and signalling.
• Manual and automatic systems.
2.1 Fire detection and fire alarms To establish the ‘best’ methods of detection and alarm, fire risk assessment should be undertaken which takes into account the type of building, construction, type of use and even the abilities of the people using the building.
2.2 Automatic fire detection The type of detection system should be arrived at from the risk assessment and take into account the environment in which the detection units will be fitted. Three types are
• heat sensitive,
• ionisation and
• optical detection.
Ionisation Detectors are sensitive to free-burning fires with flames.
Optical Detection is more effective at detecting slow-burning fires e.g. overheated electrical wiring.
Heat detection can be used in a fume-laden or dusty environment (but may not be appropriate for the rest of the protected premises).
N.B. With more and more flame-retardant treatments used in building materials and furniture, photoelectric (optical) smoke detectors tend to be the most popular choice in domestic applications.
The earliest possible warning of fire would be provided where automatic fire detectors are installed throughout all rooms and spaces in a building. As a minimum, escape routes, corridors and circulation areas should be provided with automatic fire detection.
2.3 Categories of fire alarm and detection systems and their objectives (BS5839, Part 1) Systems are designed to protect property or life and are divided into categories:
P1 and P2 for property protection. Life protection is divided into categories L1, L2, L3, L4, L5 and M. These categories determine what type of detection equipment is used and where it is placed. Also, sounder positions and quantities within the premises are a consideration within these categories.
2.4 Sub division of categories Category P systems is automatically-activated fire detection systems designed to protect property.
These systems are then sub-divided into:
Type P1 Fire system installed throughout building.
Type P2 Fire system only installed in a defined part of the building.
(Objective: to summon the fire brigade in the early stages of a fire)
Category L systems are automatically-activated fire detection systems designed to protect life. These systems are then sub-divided into:
L1 Fire system installed throughout building.
L2 Fire system only installed in a defined part of the building.
L3 Fire system only installed for the protection of escape routes.
L4 This Category is one in which detectors are only installed within escape routes. A Category L4 system is, therefore, equivalent to a Category L3 system without detectors in rooms opening onto escape routes.
L5 This Category is one in which the protected area(s) and/or the location of detectors is designed to satisfy a specific fire safety objective (other than the objectives of another sub- categories of Category L systems).
Thus, a Category L5 system may be used, for example, to address specific requirements emanating from a fire risk assessment.
(Objective: To protect people from loss of life or injury)
Common places of work, such as offices, shops, factories, warehouses, and restaurants.
M or P2/M or P1/M A Category M system normally satisfies the requirements of the legislation. It is, however, often combined with a Category P system to satisfy the requirements of insurers, as company policy for the protection of assets, or to protect against business interruption. Hotels and hostels. L1 or L2 In bedroom areas, the design
requirements are usually based on the recommendations for a Category L3 system. Detectors are, however,
typically installed in most other rooms and areas, as a fire in almost any area of the building could pose a threat to sleeping occupants; the system Category is, therefore, at least L2. In practice, few, if any, areas are left unprotected and the system Category is effectively L1, except that a variation from the recommendations applicable to a Category L1 system may apply to the siting of heat, smoke or carbon monoxide detectors in bedrooms; this often follows the recommendations of 22.3e for detectors in a Category L3 system. Large public houses. (No residential accommodation)
M -
Public houses with residential accommodation.
L2 -
Schools, other than small single story schools with fewer than 160 pupils.
M or M/P2 or M/P2/L4 or M/P2/L5
System Category is normally based on a fire risk assessment. In many schools, a Category P system is installed to combat the hazard of arson. In schools that are partly occupied at certain times (eg during evening classes or community use), a Category L4 or L5 system is sometimes considered appropriate. Hospitals. L1 (with possible minor
variations)
Detailed guidance on areas to be protected and possible variations are given in HTM 82. Places of assembly, (eg cinemas, theatres, nightclubs, exhibition halls, museums and galleries, leisure centers and casinos). Small premises (eg
M L1 to L4
L1 systems are often provided in large or complex buildings.
accommodating fewer than 300 persons). Other premises. Transportation terminals. M/L5 - Covered shopping centers. L1 to L3 The exact design needs to
be "tailor made" and often forms part of a fire engineering solution. Residential care homes. L1 to L3 L1 is regarded as appropriate
for large premises. Prisons. M/L5 - Phased evacuation buildings. L3 - Buildings in which other fire precautions, such as means of escape, depart from recognized guidance.
• Principal components of systems.
• Detection and signalling.
• Manual and automatic systems.
2.1 Fire detection and fire alarms To establish the ‘best’ methods of detection and alarm, fire risk assessment should be undertaken which takes into account the type of building, construction, type of use and even the abilities of the people using the building.
2.2 Automatic fire detection The type of detection system should be arrived at from the risk assessment and take into account the environment in which the detection units will be fitted. Three types are
• heat sensitive,
• ionisation and
• optical detection.
Ionisation Detectors are sensitive to free-burning fires with flames.
Optical Detection is more effective at detecting slow-burning fires e.g. overheated electrical wiring.
Heat detection can be used in a fume-laden or dusty environment (but may not be appropriate for the rest of the protected premises).
N.B. With more and more flame-retardant treatments used in building materials and furniture, photoelectric (optical) smoke detectors tend to be the most popular choice in domestic applications.
The earliest possible warning of fire would be provided where automatic fire detectors are installed throughout all rooms and spaces in a building. As a minimum, escape routes, corridors and circulation areas should be provided with automatic fire detection.
2.3 Categories of fire alarm and detection systems and their objectives (BS5839, Part 1) Systems are designed to protect property or life and are divided into categories:
P1 and P2 for property protection. Life protection is divided into categories L1, L2, L3, L4, L5 and M. These categories determine what type of detection equipment is used and where it is placed. Also, sounder positions and quantities within the premises are a consideration within these categories.
2.4 Sub division of categories Category P systems is automatically-activated fire detection systems designed to protect property.
These systems are then sub-divided into:
Type P1 Fire system installed throughout building.
Type P2 Fire system only installed in a defined part of the building.
(Objective: to summon the fire brigade in the early stages of a fire)
Category L systems are automatically-activated fire detection systems designed to protect life. These systems are then sub-divided into:
L1 Fire system installed throughout building.
L2 Fire system only installed in a defined part of the building.
L3 Fire system only installed for the protection of escape routes.
L4 This Category is one in which detectors are only installed within escape routes. A Category L4 system is, therefore, equivalent to a Category L3 system without detectors in rooms opening onto escape routes.
L5 This Category is one in which the protected area(s) and/or the location of detectors is designed to satisfy a specific fire safety objective (other than the objectives of another sub- categories of Category L systems).
Thus, a Category L5 system may be used, for example, to address specific requirements emanating from a fire risk assessment.
(Objective: To protect people from loss of life or injury)
Common places of work, such as offices, shops, factories, warehouses, and restaurants.
M or P2/M or P1/M A Category M system normally satisfies the requirements of the legislation. It is, however, often combined with a Category P system to satisfy the requirements of insurers, as company policy for the protection of assets, or to protect against business interruption. Hotels and hostels. L1 or L2 In bedroom areas, the design
requirements are usually based on the recommendations for a Category L3 system. Detectors are, however,
typically installed in most other rooms and areas, as a fire in almost any area of the building could pose a threat to sleeping occupants; the system Category is, therefore, at least L2. In practice, few, if any, areas are left unprotected and the system Category is effectively L1, except that a variation from the recommendations applicable to a Category L1 system may apply to the siting of heat, smoke or carbon monoxide detectors in bedrooms; this often follows the recommendations of 22.3e for detectors in a Category L3 system. Large public houses. (No residential accommodation)
M -
Public houses with residential accommodation.
L2 -
Schools, other than small single story schools with fewer than 160 pupils.
M or M/P2 or M/P2/L4 or M/P2/L5
System Category is normally based on a fire risk assessment. In many schools, a Category P system is installed to combat the hazard of arson. In schools that are partly occupied at certain times (eg during evening classes or community use), a Category L4 or L5 system is sometimes considered appropriate. Hospitals. L1 (with possible minor
variations)
Detailed guidance on areas to be protected and possible variations are given in HTM 82. Places of assembly, (eg cinemas, theatres, nightclubs, exhibition halls, museums and galleries, leisure centers and casinos). Small premises (eg
M L1 to L4
L1 systems are often provided in large or complex buildings.
accommodating fewer than 300 persons). Other premises. Transportation terminals. M/L5 - Covered shopping centers. L1 to L3 The exact design needs to
be "tailor made" and often forms part of a fire engineering solution. Residential care homes. L1 to L3 L1 is regarded as appropriate
for large premises. Prisons. M/L5 - Phased evacuation buildings. L3 - Buildings in which other fire precautions, such as means of escape, depart from recognized guidance.
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