Civil Engineering Reference
In-Depth Information
9.5.18
Methods of raising the alarm
In general alarm sounders giving audible signals must be
appropriate to the circumstances and must not be able
to be confused with any other alarm.
Research has suggested that persons respond very
much quicker and more positively to verbal instruc-
tions to evacuate a building. However, alarms are most
commonly provided by bells, sirens or beeps which may
vary in tone and pitch.
In those locations where an audible warning is
insuffi cient, e.g. where there may be persons with
impaired hearing or in a noisy working environment, the
fi re warning system should be augmented with a visual
signal. See Table 9.16 for examples of situations, together
with appropriate warning arrangements.
The nature and type of audible or other type of
alarm signals will depend upon the complexity and the
Figure 9.81
Audible fi re alarm
Table 9.16
Examples of various arrangements for raising
the alarm in case of fi re
Figure 9.82
An example of a combined audible and vis-
ual fi re alarm installed in a potentially noisy workplace
Use of building
Alarm arrangements
Cinemas
Coded message to staff followed
by a general announcement to
public to evacuate
occupancy of a building. For example, in care facili-
ties such as hospitals and residential care homes where
persons may need assistance to evacuate, the alarm
system may not necessarily be required to rouse people
from sleep but to ensure that those who are required to
assist are alerted. Clearly the audibility requirements will
vary and traditionally 65 dB(A) is accepted as the minimal
requirement, although 60 dB(A) may well be acceptable
in enclosed spaces such as offi ces (not open plan) and
in stairways.
Where members of the public frequent entertainment
or shopping facilities where the potential background
noise from music, etc. is greater than 80 dB(A) the music
should be capable of being muted when the fi re alarm
signal is actuated. Where persons need to be alerted
Prisons
Discrete alarm to staff on which
they instigate controlled evacuation
to secure external location
Hotels
General alarm suffi cient to wake
sleeping occupants and instigate
an immediate evacuation
Large offi ce
Two-stage general warning to
blocks
evacuate fl oors affected by fi re and
warn other fl oors that an evacuation
may be necessary
Factory production
Audible and visual warnings
line
signal an immediate shut down and
evacuation
