Civil Engineering Reference
In-Depth Information
items left to dry or from building to building when heat
from a fi re may be radiated to an adjacent building by
passing through windows, and igniting combustible
contents in the second building.
heated to an ignition temperature by coming into con-
tact with a burning material causes fi re to spread.
7.4.5 Fire growth
The rate at which a fi re grows will depend upon numer-
ous factors and it should be noted that a single factor
on its own may not promote fi re growth but interreacting
factors may develop a fi re more rapidly. A rapid growth
rate will have an effect upon areas such as the stability
of the building and the effectiveness of the emergency
plan to ensure that people can leave the building safely.
The fi re growth rate is generally recognised as the
rate at which it is estimated that a fi re will grow; this
includes spread of fl ame over surfaces and behind
linings, and within any part of the contents. Fire growth
rates may be categorised in accordance with Table 7.2.
Factors that may affect the growth rate include the:
Figure 7.19
Fire spread by radiation from heater to com-
bustible material
➤
Construction and layout of the building
➤
Ventilation into, throughout and out of the building
➤
Use of the building (including the types of activity
being undertaken)
➤
Fire loading within the building.
Construction and layout of the building
How the building or structure is constructed in terms of
its materials and the quality in which the materials have
been used within the building has an effect upon any
potential fi re growth rate. Clearly, buildings constructed
of wood have the potential to speed the fi re growth rate;
however, in itself, due to the nature of wood (strengthens
when it is burnt) the fi re growth rate would be affected
more by voids between fl oors, ceilings and roofs in
wooden buildings than the use of wood itself.
The size and layout of a building also has the
potential to affect the growth rate. When a building
has high ceilings, such as in the case of atria (found in
shopping malls), fi re growth is likely to be much slower
than those buildings with low ceilings, or those that
Figure 7.20
Fire spread by radiation from one building to
another
7.4.4 Direct burning
When combustible materials come in direct contact
there is a physical transfer of heat from the ignition
source to the material which in turn releases vapours
which ignite and propagate the fi re. It is true to say that
direct burning makes use of one or more of the previ-
ously discussed methods of heat transfer; however, it
is appropriate to mention this method as a reasonable
proportion of fi res are started in this way and when
Table 7.2
Fire growth rates
Category
Fire growth rate
Examples
1
Slow
Open plan offi ce - with limited combustible materials, stored or used
2
Medium
Warehouse - which is likely to have stacked cardboard boxes, wooden pallets
3
Fast
Production unit/warehouse - baled thermoplastic chips for packaging, stacked plastic
products, baled clothing awaiting delivery
4
Ultra-fast
Production unit/warehouse - fl ammable liquids, expanded cellular plastics and foam
Manufacturing, processing, repairing, cleaning or otherwise treating any hazardous goods or
materials
