Civil Engineering Reference
In-Depth Information
acceptable replacement for halon 1301. HFC-227ea has
a zero ozone depleting potential, a low global warming
potential, and a short atmospheric lifetime.
Water mist systems
Fixed water mist systems have begun to be introduced
in recent years. They can quickly extinguish large fi res in
enclosed spaces because the heat that is generated by
the fi re rapidly vaporises the water mist spray droplets
into steam. However, small fi res that have not yet heated
an enclosure or are in large open areas cannot be easily
extinguished by water mist sprays unless the fi re is liter-
ally within the range of the spray.
There are currently about 1000 systems in use in the
UK that use water mist to fl ood a compartment when
a fi re breaks out. There is some debate regarding the
effectiveness of these systems for life safety. In common
with all fl ood systems these can be fi tted to protect the
whole compartment or just specifi c fi re risks within the
compartment. These systems are currently used in both
domestic and industrial applications often as a compen-
satory feature to enable normal design parameters to be
increased. There is currently no British Standard for their
design or application.
Figure 9.66
Typical warning sign to a computer room fi t-
ted with a fl ood system
The design specifi cation of such systems is often based
on specialist experience and will usually be governed by
factors such as the type of fi re, whether the protected
area is occupied or not, the volume of space to be
inerted, etc.
Note:
halon gases were widely used in fl ooding
systems because they are extremely effi cient at
extinguishing fi res by chemically inhibiting fl ame propa-
gation. Two specifi c halons (halon 1211 bromochloro-
difl uoromethane (BCF)) and 1301 bromotrifl uoromethane
(BTM)) are very effective for many types of fi re. However,
because of their adverse effects on the depletion of the
ozone layer, their production was discontinued in 1994
as a result of the 1987 Montreal Protocol. Halon systems
can only be specifi ed if they use recycled gases.
Alternatives are being developed, for example HFC-
227ea fi re suppression agent is considered to be an
An important feature of any fl ooding system
must be the method by which the system
is prevented from being operated while the
space is occupied. In all cases the extinguish-
ing media will harm and may kill the occupants
of any confi ned space in which it operates.
Systems are often designed to be oper-
ated when the space they protect is unoc-
cupied. Other systems provide pre-warning
to occupants or rely on manual operation.
Figure 9.67
High pressure water mist system in operation
9.5.13 Portable fi re fi ghting equipment
Fire extinguishers are usually designed to tackle one
or more classes of fi re. All extinguishers that conform
to current regulations are coloured red. In order to
differentiate the specifi c type of extinguisher they display
a colour coded panel which should be at least 5% of the
