Not only should the contents and activities be
considered in relation to fire 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/m2). Some materials
generate much greater MW/m2 than others. For example,
wooden pallets that are stacked 1.5 metres high are
likely to release 5.2 MW/m2 whereas polystyrene jars
packed in cartons stacked at the same height have a
heat release of 14 MW/m2.
Table 7.3 shows some examples of common
commodities together with their known fire loading in
terms of megawatts per square metre. When considering
the fire risk associated with stored materials it is
important to think about the heat that may be generated
when materials are involved in a fire.
It is also widely recognised that the containers within
which some materials are stored add significantly to the fire
loading within buildings, most notably bulk warehouses.
The Hazardous Installations Directorate report on chemical
warehouse hazards states that flammable 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/
m2 to the total rate of heat release each.
As can be seen from the examples above and the
issues discussed in both construction and ventilation,
fire growth is not based on any one element but
a combination of all. This will need to be taken into
account when undertaking fire risk assessments and any
subsequent action plans.