Civil Engineering Reference
In-Depth Information
Operating lever
Safety pin
Control valve
Pressure relief device
Valve spring
Dischargetube
Gaseous CO
2
Dischargehorn
Liquid CO
2
Figure 9.71
Wet chemical fi re extinguisher
portable fi re extinguishers. Those provided should also
satisfy legal and insurance requirements.
In general, extinguishers and fi re blankets should be
positioned at locations where they are conspicuous and
readily accessible for immediate use.
Extinguishers for general protection should be:
Figure 9.70
Carbon dioxide extinguisher
that involve electrical equipment; however, they have a
number of disadvantages:
➤
Near stairways
➤
In corridors or landings
➤
When they operate they are very noisy and as a
result can distract the operator
➤
They only operate for a limited period; the smaller
ones may last only 12 seconds
➤
Close to exits.
Extinguishers should not be located:
➤
They do not cool the fi re and therefore fi re can easily
reignite unless the CO
2
is periodically reapplied
➤
Where a potential fi re might prevent access to them
➤
In concealed positions behind doors, in cupboards
or deep recesses
➤
In positions where they might cause obstruction to
exit routes or be damaged by trolleys or vehicles
➤
They do not work in an open area where draughts
may cause the CO
2
to disperse.
Wet chemical
- wet chemical fi re extinguishers have
been developed specifi cally for use on fi res involving
cooking oils and fats. They are the most effective type
of extinguisher for this type of fi re risk. The extinguishers
work by discharging the wet chemical agent, through a
spray type nozzle, onto the surface of the burning oil or
fat. The wet chemical agent reacts with the burning oil or
fat to form a 'suds-like' blanket across the fuel surface.
This 'suds-like' blanket extinguishes the fi re by exclud-
ing the air, and by preventing the release of fl ammable
vapours.
Table 9.13 provides a summary of information relating
to the various types of extinguishers and media.
➤
Over or close to heating appliances
➤
Where they may be subjected to extremes of heat
or cold
➤
Where they are exposed to wet or damp
atmospheres.
Extinguishers provided to deal with special fi re risks
should be sited near to the fi re risk concerned, but not
so near as to be inaccessible or place the operator in
undue danger in case of fi re.
Where large undivided fl oor areas necessitate
positioning appliances away from exits or outer walls,
they should be installed on escape routes. They should
be positioned so that it is not necessary to travel more
than 30 m from a fi re to an extinguisher.
Extinguishers should be mounted on brackets so
that the carrying handle is 1 m above the fl oor for large
extinguishers and about 1.5 m for smaller ones. Potentially
dangerous siting should be avoided. For example, foam
Siting of portable extinguishing equipment
Extinguishers should be provided in numbers and sizes
recommended by BS 5306 - Fire extinguishing instal-
lations and equipment: on premises: Part 3: Code of
Practice for selection installation and maintenance of
