Product guide

page
21
APPLICATION OF
DISCOVERY DETECTORS
The process of designing a fire detection
system using Discovery detectors is the same
as that used for any other detector range,
except that Discovery offers more choices to
the system designer. The principles set out in
relevant codes of practice such as BS5839:
Part 1 should be followed in any system
design. The notes below are intended to
supplement the codes of practice and to give
some specific guidance on the choices
available with the Discovery range.
Choice of Detector Type
The choice of detector from
the Discovery range follows
the well-established
principles of system design.
That is, the optimum
detector type will depend on
the type of fire risk and fire
load, and the type of
environment in which the
detector is sited.
For general use, smoke
detectors are recommended
since these give the highest
level of protection. Smoke
detectors from the Discovery
range may be ionisation,
optical or multisensor types.
It is generally accepted that
ionisation types have a high
sensitivity to flaming fires
whereas optical detectors
have high sensitivity to
smouldering fires. As a result
of this, ionisation types are
widely used for property
protection, and optical types
for life protection. These
general principles still apply
to the Discovery detectors,
although the availability of a
multisensor in the Discovery
range offers more choice to
the system designer.
The multisensor is basically
an optical smoke detector
and will therefore respond
well to the smoke from
smouldering fires. In
response modes 1, 3 and 4,
however, (ie, in the
multisensor modes) the
detector also senses air
temperature. This
temperature sensitivity
allows the multisensor to
give a response to fast
burning (flaming) fires which
is similar to that of an
ionisation detector. The
multisensor can therefore be
used as an alternative to an
ionisation detector while still
retaining the benefits of an
optical smoke detector.
Where the environment is
smoky or dirty under normal
conditions, a heat detector
may be more appropriate. It
must be recognised,
however, that any heat
detector will respond only
when the fire is well
established and generating a
high heat output. The
Discovery heat detector can
be used in a wide range of
DISCOVERY
Ionisation Optical Multisensor Heat CO
Overheating/thermal decomposition
Poor Very good Very good Very poor Very poor
Smouldering/glowing combustion Moderate/Good Good Good Very poor Excellent
Flaming combustion Very good Good Good Poor Poor
Flaming with high heat output Very good Good Very good Moderate/good Moderate
Flaming – clean burning Poor Very poor Moderate/good Moderate/good Very poor
Table 6 Relative performance of detectors in test fires