Categories (Types) of System
Two new 'Categories' of system have
been introduced. (The term 'Category' replaces the term Type' used
in the previous code). These are Category L4 and L5 systems.
A Category L4 system 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.
A Category L5 system 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 other 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. A Category L5
system could, of course, be as simple as one smoke detector in the
access room associated with an inner room that has no vision panel
between it and the access room.
See
some recommended categories of systems
Travel Distance to Manual Call
Points
For most applications, the maximum
distance that anyone should have to walk to reach the nearest break
glass call point has been increased from 30m to 45m. If a designer
does not, however, know the final layout of an area, the code
recommends that the direct (straight line) limitation between any
point and the nearest manual call point should be 30m.
However, where processes in an area result in the likelihood of
rapid fire development, or where it is likely that the manual call
points will be used by occupants of limited mobility, the above
figures are reduced from 45m to 25m and 30m to 16m respectively.
Sound Pressure Levels
The new code provides for greater
flexibility in sound pressure levels. The existing 65dB(A) minimum
is reduced to 60dB(A) in stairways, cellular offices and similar
enclosures of no more than approximately 60m2 in area and what the
code describes as 'specific points of limited extent'. The purpose
of the last of these relaxations is to avoid the need for additional
sounders simply because the sound pressure level is a few dB less
than the recommended 65dB(A) within a small defined area.
The code also acknowledges that
different sound pressure levels will apply in the case of patient
care areas of hospitals, to which the recommendations of HTM 82
apply. A relaxation from the 75dB(A) at the bedhead of bedrooms may
also apply in the case of certain residential care premises in which
the fire alarm system is not intended to rouse the occupants from
sleep.
Fire Resistance of Cables
The first change in this respect is
that fire resisting cables are now recommended for all parts of the
fire alarm system, including the mains supply cables. The use of
non-fire resisting cables, whether protected by fire resisting
construction or not, will no longer comply with the code.
With regard to the two levels of fire
resistance described earlier, the code acknowledges that standard
fire resisting cables (which, effectively, means virtually all fire
resisting cables now in use) are suitable for the majority of
applications. Cables of enhanced fire resistance (which would
include most mineral insulated copper sheathed cables) are only
specifically recommended in the following circumstances:
-
Unsprinklered
buildings of greater than 30m in height.
-
Unsprinklered
buildings (or parts of buildings) in which the fire strategy
involves evacuation of occupants in four or more phases.
-
In
certain Unsprinklered premises or sites in which people remain
in occupation during the course of a fire; in such cases,
cables of critical signal paths running throughout the
premises or site would need to have enhanced fire resistance.
An example is a large hospital with central control equipment.
-
In
certain situations in which the role of a fire detection and
alarm system in a fire engineering solution is judged by the
enforcing authority to be sufficiently critical to warrant
cables of enhanced fire resistance.
Routine Servicing
There was much controversy, during
the public comment phase, regarding the periods at which fire alarm
systems should be serviced. The new code recommends that the period
between successive inspection and servicing visits should be based
upon a risk assessment. However, the recommended period between
successive visits should not exceed six months. In effect, this
means that, in many cases, six monthly servicing will be acceptable
rather than the previously recommended quarterly servicing.
Standby Battery Capacity
Recommendations in respect of standby
battery capacity have been greatly simplified. For Category M and L
systems, the standby period recommended is 24 hours, after which
sufficient capacity should remain to give an evacuation signal for
30 minutes. (Although this duration is now virtually custom and
practice, the previous code actually recommended longer standby
periods in some situations.) The duration may be reduced to six
hours if there is an automatically started standby generator.
For Category P systems, the
recommended standby duration is 24 hours longer than the maximum
period for which the premises will be unattended, but an upper limit
of 72 hours is recommended.
Limitation of false alarms
Substantial hopes have been pinned on
the new code to make a major impact on the number of false alarms
that are generated by automatic fire detection and alarm systems. In
the year 2000, over a quarter of a million false alarms were
generated by fire alarm systems.
As indicated earlier in this article,
the major responsibility for avoidance of false alarms is imposed on
the designer. However, the installer has a minor role to play in
ensuring that no obvious potential for false alarms exists. The code
recommends that the commissioning engineer carry out a special check
in this respect. The user is expected to manage the building and the
system properly in order to minimize false alarms. When the system
is serviced, under the new code it is the responsibility of the
servicing organization to monitor the false alarm record and to
provide suitable advice where appropriate. New benchmark figures for
anticipated and acceptable rates of false alarms are incorporated
within the code.
In addition, specific and detailed advice on a number of
considerations that should limit false alarms are given. These
relate to the following matters:
-
Siting
and selection of manual call points.
-
Selection
and siting of fire detectors.
-
Selection
of system type (e.g. conventional, analogue or multi-sensor).
-
Protection
against electromagnetic interference.
-
A
'soak test', whereby systems with more than 50 automatic
detectors are placed on 'soak' for at least a week before
being
brought into operation.
-
Measures
for filtering false alarms, such as time-related systems and
systems that incorporate an investigate period for staff
before sounding of alarms and/or summoning the fire brigade.
-
Management
of the system by the user.
-
Routine
servicing.
