Civil Engineering Reference
In-Depth Information
➤
Assisting the safety briefi ng of employees, visitors,
contractors, etc.
➤
Assisting fi re service operations at the time of an
emergency.
If the warning is perceived as a precautionary
measure the decision to move may be delayed or in some
circumstances even ignored. This will be infl uenced by
the experience of any previous unnecessary evacuations.
As previously discussed the UK standard for fi re warning
systems is given in BS 5839-1:2002, which outlines the
requirements for these signals.
Audible alarm signals
- it is essential that audible
alarm systems are suffi cient in nature and volume that
all those persons for whom it is intended are able to
recognise it for what it is. In general a sound level of
60 to 65 dB(A) is considered appropriate. Additional
requirements will be required when workplaces have
higher background noise levels or where people will
need to be roused from sleep.
A critical factor to also consider in the use of audible
alarms is the possibility that a workplace may have
a number of alarms that could be of the audible type,
such as pressure alarms, boiler alarms and burglar/
security alarms. Selecting the correct alarm to ensure
people know what is expected of them is essential if
the response in the event of a fi re emergency is to be
successful.
Research has been conducted into the effective-
ness of providing audible speech warnings incorporating
evacuation instructions. Informative fi re warning systems
are found to be more effective than a conventional fi re
tone alarm in encouraging a prompt evacuation and also
provide specifi c details of directions to take, etc.
Over recent years, particularly within large places
of public assembly such as shopping centres, sports
stadia, etc. emergency voice communications (EVC)
systems have been utilised; BS 5839 Part 9 provides
detailed information of the system requirements. EVCs
are intended for specifi c types of communication; they
are not, for example, designed for general use for non-
emergency purposes.
EVC systems are intended for:
10.2.2 Detection
In order to maximise the amount of time that people in
buildings have to escape a fi re it is important to ensure
that there are adequate arrangements for detecting a fi re
as soon as one breaks out.
All fi res give off heat, light and smoke, each of
which can be detected by a variety of means. In some
small premises that are occupied around the clock, it
may be suffi cient to rely on human detection, i.e. people
smelling the smoke or seeing the fl ames. In most cases,
however, some form of automatic system is the only
means of achieving adequate detection of a fi re.
Providing automatic fi re detection in zones often
results in a quicker identifi cation of the location of the
fi re and can provide an overview of the extent of fi re and
smoke spread throughout the building which will aid
evacuation and response.
In the case of a multiple storey building the fi re
detection system is often zoned in fl oors which allows
for appropriate sequential evacuation of the occupants
if necessary. Chapter 9 discusses in detail automatic fi re
detection systems.
10.2.3 Warning signals
Confi rmation that there is a requirement for an emer-
gency evacuation is totally reliant on the perception of
the person reporting the incident and his or her ability to
comprehend the situation and possible impact.
There should be a simple system in place to enable
confi rmation and activation of the emergency action
procedure. This in turn will depend on the communica-
tion of reliable information about the risk and/or the level
of exposure to hazards.
➤
Use by the management of the building or complex
for initial evacuation in the fi rst stages of evacu-
ation, before the fi re service arrives. The EVC system
Figure 10.15
Smoke detector
Figure 10.16
Audible warning devices
