Fire Protection
Procedure & Guidance
Fire Alarm Systems
Ref
Issue/Revision Date
01/10/2010
Review Date
21/05/2015
Version
FS- NFG002
8.0
Background
This Note for Inspecting Officers provides guidance on the standards that are considered appropriate
in respect to fire alarm systems.
The Note aims to set general principles and to provide the reader with information as to which
approved document or technical standard is considered by this Authority to be appropriate.
Introduction
Officers are expected to use their judgement to ensure that any fire alarm and detection system they
require, or recommend, is reliable for the level of fire risk involved. A clear distinction should be drawn
between systems intended for life safety and those designed solely for property protection.
For existing premises in West Yorkshire, Inspecting Officers will adopt the standards for fire alarm
systems advocated in the guidance notes issued by the DCLG, i.e.
Entry Level Guide - A short guide to making your premises safe from fire
Guide 1
Offices and shops
Guide 2
Factories and warehouses
Guide 3
Sleeping accommodation
Additional guidance for domestic flats is available in the Local Government Group publication
Fire safety in purpose-built blocks of flats.
Guide 4
Residential care premises
NASHiCS and CFOA felt that additional guidance was required for use with some areas of the
government’s guide No4. The additional guidance is available on both the CFOA and
NASHiCS websites so officers can download and print copies at their convenience. This
guidance covers a number of topics including: evacuation of a protected zone in two and a half
minutes, the issue of residents who are unable to be evacuated and staff remaining with them,
the use of external fire escapes, the travel distance to evacuation routes and the use of bypass routes.
Guide 5
Educational premises
Guide 6
Small and medium places of assembly
Guide 7
Large places of assembly
Guide 8
Theatres and cinemas
Guide 9
Outdoor events
Guide 10
Healthcare premises
Guide 11
Transport premises and facilities
Guide 12
Animal premises & facilities
Means of escape for disabled people (Supplementary guide)
Page 1 of 4
For new systems, and for certain more complex premises, other guidance documents will be used as
appropriate. For example:
British Standards BS 5839: Part 1 "Code of practice for system design, installation and servicing"
BS 5839: Part 6 "Code of practice for the design and installation of fire detection and alarm systems in
dwellings"
BS 58391: Part 8 "Code of practice for the design, installation and servicing of voice alarm systems ",
Although BS 5839: Part 6 is primarily concerned with the installation of fire alarm systems for a range
of domestic properties, the recommended standards may be suitable and appropriate for some small
workplaces
Smoke Detectors and Smoke Alarms (Ionisation V Optical)
There have been a number of research projects recently that have examined the effectiveness of
smoke detectors. As specifiers of automatic fire alarm systems, we should be aware of the advantages
and disadvantages between the main two types of smoke detectors available on the market (i.e.
Optical and Ionisation).
Optical (photoelectric) smoke detectors operate by detecting the scattering, or absorption, of light by
smoke particles inside a detection chamber. In ionisation detectors, an electric current flowing through
an ionisation chamber is reduced when smoke particles enter it.
Ionisation chamber smoke detectors are particularly sensitive to smoke containing small particles such
as are produced in rapidly burning flaming fires. However, they may be less sensitive to the larger
particles found in optically dense smoke, which may be produced by smouldering materials. Ionisation
chamber detectors may be more appropriate type for installation in rooms, such as the living room or
dining room, where a fast-burning fire may present a greater danger to occupants than a smouldering
fire.
Optical smoke detectors are sensitive to the larger, optically active particles found in slow burning or
smouldering fires (a most important consideration taking account of the introduction of many flameretardant materials currently used in fabrics, furnishings and building products). Further general
advantages of optical smoke detectors include their stability when subjected to a wide range of
physical and climatic variations. In areas where air movement, temperature change, humidity and
changes in air pressure are likely to occur, optical smoke detectors can be expected to remain more
stable whilst reacting to the majority of fires
Optical detectors are also more sensitive to smoke that has travelled some distance from the seat of
the fire, during which time smoke particles have cooled and coalesced to form larger particles, making
them more effective on escape routes in systems designed for life protection.
Carbon Monoxide Detectors
Carbon Monoxide (CO) is a toxic gas produced by fires and responsible for a high proportion of fire
fatalities. CO is odourless, colourless and tasteless making it almost impossible for people to be
aware of its presence. Exposure to relatively low levels for just one or two minutes can lead to
permanent brain damage or death. Lower levels of CO can cause disorientation and collapse during
physical exertion thus hampering the ability of victims to escape.
For many years it has been known that CO detectors can be used as a means of providing early
warning of fire. Especially in slow developing and smouldering fires where CO is produced
significantly before traditional detectable smoke (aerosols and particulates).
1
Note/ BS 5839 Part 8 expands the recommendations given in clause 9.12 of BS 5839: Part 1: 1988. It should be read in conjunction with
BS 5839: Part 1; BS 6259; and BS 7443
Page 2 of 4
Because CO is a gas and more mobile than smoke, detector positioning relative to the seat of a fire is
less critical, giving a higher likelihood of early detection. Smoke movement is constrained by
convection currents created by the fire, whereas CO, being a gas, is much more mobile than smoke
and also moves by diffusion. This provides an advantage for the CO fire detector allowing a high
tolerance on where the detectors can be located.
Advantages
CO detectors will detect fire from outside the closed door of a cupboard, bedroom or cabin
before spreading outside the room. This helps to detect fires whilst the means of escape is still
clear.
CO detectors will continue to detect even if incorrectly mounted on a wall or under floor.
CO detectors will operate where thermal barriers inhibit smoke movements such as hot roof
spaces in atria and metal roofed buildings.
CO detectors will operate on beamed ceilings, which present obstructions to possible smoke
flow.
Carbon Monoxide fills a space evenly and the CO fire detector is far less sensitive to the point
where the fire started.
Applications include: Warehouses & large covered areas.
Large foyers, halls & reception areas
Cinemas, theatres, concert halls
Sports halls & large waiting areas
Hotel rooms and changing rooms where steam and water mist can cause problems.
Production facilities where large quantities of dust are produced.
Production facilities where chemical vapours cause traditional detectors to false alarm.
Kitchens and restaurants where burnt toast and similar causes of false alarm are prevalent. (In
these circumstances the alarm threshold will only be reached once the toast is actually
burning).
Farm buildings with high levels of dust and other airborne materials.
Disadvantages:
The effective life of the detector may only be 5 years.
Some fires generate little or no CO and as such are not suitable for protection via the Carbon
Monoxide fire detector. Such fires include the early stages of electrical fires and burning
cables where aspirating systems are more suitable.
CO fire detectors would not detect other non-carbon fires such as pure metal fires.
CO fire detectors are also unsuitable for protection of areas where fast burning chemical fires
represent the main hazard. In this case ion-chamber or flame detectors are more suitable.
Duct probe units in heating and air conditioning ducts are best suited to use with optical fire
detectors. The use of CO fire detectors and ionisation detectors is not recommended under
normal circumstances for duct air sampling applications.
CO fire detectors will only operate in situations where combustion takes place; it will not detect
smoke and fumes alone.
Page 3 of 4
After considering the above guidance, and subject to a site-specific risk assessment, Inspecting
Officers may accept/recommend CO detectors (Only types third party approved) as an alternative to
heat and smoke detectors inside rooms.
Optical smoke detectors should be recommended for circulation areas such a corridors and stairways,
unless the need to prevent false alarms becomes essential. The siting of the detectors should be in
accordance with the recommendations of BS 5839: Parts 1 or 6.
Page 4 of 4