Civil Engineering Reference
In-Depth Information
➤
Healthcare premises
➤
Transport networks.
Not only should the contents and activities be
considered in relation to fi re growth, but also the
arrangements for the storage, of materials with potential
for high heat release.
Heat release from materials is measured in
megawatts per square metre (MW/m
2
). Some materials
generate much greater MW/m
2
than others. For example,
wooden pallets that are stacked 1.5 metres high are
likely to release 5.2 MW/m
2
whereas polystyrene jars
packed in cartons stacked at the same height have a
heat release of 14 MW/m
2
.
Table 7.3 shows some examples of common
commodities together with their known fi re loading in
terms of megawatts per square metre. When consid-
ering the fi re risk associated with stored materials it is
important to think about the heat that may be generated
when materials are involved in a fi re.
It is also widely recognised that the containers within
which some materials are stored add signifi cantly to the fi re
loading within buildings, most notably bulk warehouses.
The Hazardous Installations Directorate report on chemical
warehouse hazards states that fl ammable liquids in plastic,
intermediate bulk containers (IBCs) present a very high risk
because they inevitably fail in the case of a fi re releasing
their contents, adding, as a rule of thumb, around 3 MW/
m
2
to the total rate of heat release each.
As can be seen from the examples above and the
issues discussed in both construction and ventila-
tion, fi re growth is not based on any one element but
a combination of all. This will need to be taken into
account when undertaking fi re risk assessments and any
subsequent action plans.
Clearly, the use to which a building is put will greatly
infl uence the contents within. In addition the quantity
of combustible and fl ammable materials within a build-
ing will also refl ect its use. The nature of the contents of
a building is a key factor in determining the rate of fi re
growth and spread in the event of fi re.
Fire loading within the building
The contents of the building and therefore the growth
rate of a fi re will vary according to the materials and
activities being used or undertaken, for example where
a signifi cant amount of dangerous substances or prepar-
ations, e.g. substances or preparations that have a fast
or ultra-fast fi re growth rate or are classifi ed as explo-
sive, oxidising, extremely fl ammable, highly fl ammable
under the Chemicals (Hazard Information and Packaging
for Supply) Regulations 2002, are stored and/or used,
the area is considered to be of high fi re risk.
When large quantities of readily combustible
products are stored or displayed under a large open plan
mezzanine or gallery with a solid fl oor (as in some DIY
outlets) there is always a risk of rapid fi re growth resulting
in fl ames spreading beyond the edge of the mezzanine or
gallery fl oor, hence posing a threat to life safety, particu-
larly when the occupants of the building are members of
the public and are likely to be unfamiliar with the
emergency plan (builders' merchants, DIY stores, etc).
Table 7.3
Common commodities together with their
known fi re loading
Commodity
Heat release
MW/m
2
Wood pallets, stack 0.46 m high
1.4
(5-12% moisture)
Wood pallets, stack 1.5 m
5.2
high (5-12% moisture)
Wood pallets, stack 3.1 m high
10.6
(5-12% moisture)
Polyethylene rubbish litter bins in
2
cartons, stacked 4.6 m high
Polystyrene jars packed in cartons,
14
compartmented, stacked 1.5 m high
Polystyrene tubs nested in cartons,
5.4
stacked 4.3 m high
Figure 7.22
Example of fi re load from storage containers
in a warehouse
20-25 video cassettes
1
