SELECTION
AND SPECIFICATION OF FIRE ALARM CATEGORY IN ACCORDANCE WITH BS 5839-1
“Categories” of fire alarm system were first
introduced into BS 5839-1 in 1988 - when they were described as “Types” of
system. In the 2002 revision of BS 5839-1, two new Categories were added, L4
and L5. However, there still remains confusion, particularly amongst users,
specifiers and fire risk assessors, regarding the application of these
categories and the responsibility for specifying the appropriate category for
any building.
The purpose of this guidance
document is to clarify the responsibility for identifying the appropriate
category of system, and to give general guidance on the typical category that
is appropriate for different building uses.
This guide incorporates extracts
from The Design, Installation, Commissioning and Maintenance of Fire
Detection and Fire Alarm Systems by Colin S. Todd, whose assistance in
preparing this guide is gratefully acknowledged.
2.
The Categories
BS 5839-1 defines eight
categories of system, according to whether the system is purely manual or
incorporates automatic fire detection, and, in the latter case, the purpose and
extent of the automatic fire detection.
The eight categories of
system are defined as follows:
Category M systems:
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These are manual systems and therefore,
incorporate no
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automatic fire
detectors.
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Category L systems:
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These are automatic fire detection
systems intended for
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the protection of life.
They are further subdivided into the
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following subcategories
of system as follows:
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Category L1:
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Systems installed throughout all areas
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of the building.
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Category L2:
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Systems installed
only in defined parts
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of the building,
including all parts
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necessary to satisfy
the
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recommendations
of the code for a Category L3 system. The additional areas protected, over and
above those protected in a Category L3 system, are those in which there is
either high likelihood of fire starting or a high risk to life if fire does
start.
3.
Responsibility for Selection of System Category
Since there are eight system categories defined in BS 5839-1, a
reference to BS 5839-1 without a reference to a system category, for example,
in a purchase specification; enforcement notice under fire safety legislation;
or a fire risk assessment would be virtually meaningless. Within statutory
requirements imposed by enforcing authorities - as part of any requirements
imposed by property insurers and in any action plan of a fire risk assessment -
the category of system to be installed should always be included in a
specification. In addition, other than in the case of a Category M, L1, P1 and
L4 system, further information needs to be included regarding the areas of the
building that are to be protected by automatic fire detection. In a Category M
system, there
are no such areas, while all
areas are protected in a Category L1 or P1 system, and only the escape routes
are protected in a Category L4 system.
In particular, it should be stressed that the responsibility for
determining the appropriate system category for any application does not rest
with the designer of the fire alarm system, such as a fire alarm contractor,
who is not expected to have sufficient expertise in the principles of fire
safety to come to a decision in this respect. Although many fire alarm
designers may fortuitously have such expertise, the decision rests with the
fire safety specialist rather than the fire alarm system specialist.
Thus, it may be considered that there is something of a “firewall”
between the role of the fire safety specialist and the fire alarm system
specialist. The information that is communicated between these two parties is
the system category (see Figure 1). Moreover, it will be noted from Figure 1
that, in the case of certain categories, additional information also needs to
be communicated.
The additional information that needs to be provided in the case of certain
system categories is as follows:
Category
L2: The rooms or areas that
need to be protected, over and
above those that require to be protected
in a Category L3
system, and the type of detector
to be provided.
Category
L3: The type of detector to be
provided in rooms or areas
opening onto escape routes.
protected, and the types of detectors to
be installed. This
decision may arise from a fire risk
assessment but it is a
misconception that
this will always
be the case;
for
example, it may simply be that detectors
are required to
operate fire protection measures
(such as fire doors) or are
being installed in lieu of vision panels
to give an early
warning to those in an inner room
of a fire in an access
room.
Category
P2: The rooms or areas that
are to be protected and the types
of detector that are to be installed. This
decision may arise
from a
form of property
protection, or business
interruption; risk assessment or may be
dictated by the
requirements of property or
business interruption insurers.
Although the system purchaser or
their agent should inform the system designer as to which system category is
required (e.g. via a tender specification), in practice this commonly does not
occur as a result of a lack of understanding on the part of users and
specifiers of the principles described above. If this does not occur, BS 5839-1
recommends that the designer make the purchaser or the purchaser’s agent clear of
the category of system that is proposed prior to an order for the system being
placed. This is to avoid disputes during the course of a contract regarding the
form of system that is required and the areas that should be protected. In such
cases, the FIA recommends that contractors protect their liability by
recommending to purchasers that before placing an order for the system, they
should seek further advice from a competent person or the relevant enforcing
authority to ensure that the system proposed satisfies the requirements of
legislation and the insurer of the property.
4.
Selection of System Category
Given that purchasers and
specifiers are often unable to articulate the category of system required and
any additional information that should be provided, it is of value for
contractors and designers to have a good awareness of the category of system
that will commonly be appropriate. The guidance below is intended to assist in
this respect.
A Category M system is generally
sufficient to satisfy the requirements of fire safety legislation in workplaces
in which no-one sleeps. In the case of premises in which people sleep, quite
extensive automatic fire detection is normally required. Generally, this will
be a Category L2 or L1 system. In premises with cellular accommodation such as
hotels, there is in fact, very little difference between a Category L2 and a
Category L1 system. In a hotel or similar sleeping risk, the bedroom floors are
generally protected by a system that is effectively equivalent to a Category L3
system but additional detection is provided throughout the premises, thereby
making the system a Category L2 or Category L1 system.
Possibly,
the least likely subcategory of Category L system to be specified would be a
Category L4 system, in which automatic fire detection is provided only in
escape routes. To ensure adequate warning of occupants before escape routes are
made impassable by the presence of smoke (as would normally be required in a
sleeping risk), at least a Category L3 system would normally be required.
However, there may be
circumstances in which a Category L4 system would be appropriate; for example
(as noted above) - although workplaces in which no-one sleeps need only have a
manual fire alarm system to comply with legislation - some employers provide
limited automatic fire detection to enhance the safety of occupants beyond the
minimum legislation requirement. This may occur, for example, because some
employees might work alone in a large building after normal office hours. If
the offices are cellular in nature, a Category L3 system rapidly becomes akin
to a Category L1 system, at very significant expense. It is sometimes argued
that the installation of detectors only within escape routes provides
significant enhancement of the safety of those employees at a much lower cost.
It is becoming increasingly
common for automatic fire detection to be provided as one component of a fire
engineering solution, in which a “package” of fire precautions is provided to
satisfy the life safety objectives of legislation, without necessarily
following, exactly, the “prescriptive” Codes of Practice that apply under the
legislation. Fire risk assessments carried out to satisfy legislation can also
identify the need for some form of fire detection, perhaps within a localised
area, that does not always need to comply with the recommendations of BS 5839-1
for a Category L1, L2, L3 or L4 system. Such a system would, therefore, be a
Category L5 system.
As noted above, the purpose of a
Category L5 system is to support a specified fire safety objective or address a
particular fire safety problem. It should, therefore, be possible to articulate
the exact objective that the Category L5 system is designed to achieve. Again,
this is solely the responsibility of the fire safety specialist, rather than
the designer of the fire alarm system.
However, a Category L5 system
can, in some cases, be very simple in nature. For example, in the design of
means of escape, there is a fundamental principle that occupants of an “inner
room”, from which escape is possible only by passing through a further
(“access”) room, must have adequate means of warning them of a fire in the
access room. This is most commonly achieved by the provision of a vision panel
between the inner room and the access room. However, an alternative is to
provide smoke detection within the access room. This principle could result in
a very small number of detectors (even one) in the largest of buildings. The
resulting Category L5 system would normally be provided in conjunction with a
manual fire alarm system. The resulting system would then be described as a
Category M/L5 system.
It follows from the above, that
it should never be the case that a specifier simply calls for a Category
L5 system without information as to the areas that are to be protected by
automatic fire detection. It should never be the case that the fire
alarm contractor needs to carry out a fire risk assessment to determine the
design of a Category L5 system. It is much more likely to be the case that a
fire risk assessment has identified and determined the need for fire detection
in only specific areas. However, as previously stated, it is not always the
case that the need for a Category L5 system arises specifically from a fire risk
assessment.
While
Category P systems may well greatly enhance life safety within a building, that
is not their objective, which is purely protection of property or protection
against interruption to the normal operations of the company as a result of fire.
By providing early warning of a fire, enabling early extinguishment, it might
be said that a Category P system, as in the case of any automatic fire
detection system, also protects the environment by reducing the pollutants that
will be produced by the fire and the amount of contaminated fire-fighting
run-off water. For the highest level of protection, a Category P1 system would
be provided, particularly in buildings that are critical to the operations of
the company. In a Category P2 system, fire detection is installed in areas of
high fire hazard or in areas in which the risk to property or business
continuity from fire is high.
Annex A of BS 5839-1, which is
reproduced as Appendix 1 of this guide, gives advice on the category of system
that is typically installed in various types of premises. As the Annex is
purely informative, its purpose is not to recommend these systems for the types
of premises in question but simply to provide information on custom and
practice, and on the conventional interpretation of fire safety legislation.
More specific guidance on the systems necessary for compliance with legislation
is contained in the next subsection of this guidance document.
5.
Legislative Requirements
In virtually all new
buildings, a fire alarm system will be required by building regulations.
In England and Wales, guidance on
compliance with the Building Regulations 2010 is given in Approved Document B,
which subscribes to the view that automatic fire detection systems are not
normally needed in non-residential occupancies. However, Approved Document B
acknowledges that, even in non-residential occupancies, fire detection may be
needed:
% to
compensate for some departure from the guidance elsewhere in Approved Document
B (e.g. relating to means of escape from fire)
% as part
of the operating system for certain fire protection systems, such automatic
door releases or smoke control systems
% where a
fire could break out in an unoccupied part of the premises and prejudice the
means of escape from any occupied parts of the premises
% in a
building with phased evacuation, in which case, a system complying, at least,
with the recommendations for Category L3 is advocated
In
Scotland, guidance on compliance with the Building (Scotland) Regulations 2004
is contained in the technical handbooks that support the Regulations. The
Scottish guidance is more onerous for some premises than the equivalent
guidance in England and Wales. For example, automatic fire detection is
recommended for entertainment and assembly buildings if there are more than 60
occupants; for the largest premises, a Category L1 system is recommended.
Similarly, automatic fire detection is recommended for shops with more than 100
occupants; for the largest premises, a Category L3 system is recommended. For
specific new buildings in Scotland, the relevant technical handbook should be
consulted. It should also be noted that the Scottish technical handbook
specifies the remote transmission of alarms to an alarm receiving centre in the
case of residential care homes, hospitals and shopping centres.
The Northern Ireland Technical
Booklet E provides guidance on compliance with the Building Regulations
(Northern Ireland) 2000. For non-domestic premises, the technical booklet
requires only a system complying with BS 5839-1, although there are specific
situations in which automatic fire detection is recommended.
For existing buildings,
Government guidance on compliance with fire safety legislation gives advice on
fire alarm systems. Appendix 2 to this guide summarises the Government guidance
for existing buildings, as set out in the relevant guides for both England and
Wales and Scotland. Until appropriate guidance is published in Northern
Ireland, the guidance applicable to England and Wales can be used in Northern
Ireland.
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ANNEX A OF BS 5839-1:
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ANNEX A OF BS 5839-1:
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