Introduction to Fire Safety Management

Figure 7.15
Class ‘F’ fi res
It is worthy of note that there is no classifi cation for 
electrical fi res
; this is due to the fact that electricity 
does not actually involve any fuels which can be extin-
guished. Fires that involve electrical circuits and appli-
ances, cables, etc. can either be extinguished with a 
non-conductive extinguishing medium, or the supply can 
be isolated and the actual material (given its own ‘class’) 
can be extinguished.
Figure 7.16
Boxes containing matches being stored 
adjacent to a light fi tting
Figure 7.14
Class ‘D’ fi res

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Principles of fi re and explosion
123
unburnt fuel (unburnt products of pyrolysis) in the smoke 
can reignite on reaching its spontaneous combustion 
point causing a substantial rise in temperature. This 
rise in temperature, if provided with a fresh source of 
oxygen (window glazing fails), has the ability to cause a 
fl ashover or explosion.
Clearly there is a substantial difference in a fi re 
starting in a confi ned area such as a building, in compari-
son to one that starts in the open air and it is this issue 
that will need to be addressed when designing buildings 
that minimise smoke and fi re spread enabling people to 
escape safely.
Convection and the effects of smoke
Although it is important to restrict the spread of fi re 
within a building, it is equally important to consider the 
speed of spread and effect of the smoke created by the 
fi re as it burns.
As a fi re develops it will create large quantities of 
smoke which will, usually, spread ahead of the fi re quickly 
fi lling a building. The effect of this is to present a toxic 
and/or asphyxiant hazard to people within the building. 
Smoke also reduces visibility and obscures escape 
routes; this linked to people’s natural reluctance to walk 
into or through smoke can lead to, or increase, panic, 
which in turn leads to disorientation reducing the chances 
of safe escape.
considerably according to the type of material, e.g. metal 
is a much better conductor than brick. It should be 
noted that conduction may occur in solids, liquids or 
gases; however, in relation to fi res within buildings it is 
most prevalent in solids.
The thermal conductivity (the ability to conduct heat) 
varies between materials and is a key element in building 
design and construction, which will be con 
sidered in 
Chapter 9.
A fi re in one room can spread to adjacent rooms by 
heat being conducted through the fabric of the building 
(walls/ceilings, etc.), especially via metal pipes or frames 
used in building construction. The heat can then ignite 
materials in direct contact with the surface, or radiate 
out from the surface. This can raise the temperature 
of materials in the adjacent room to their spontaneous 
combustion temperature, thus spreading the fi re.
The relative conductivity of building materials is 
therefore an important factor in the fi re resisting ability 
of a structure or building. This issue is considered within 
the Building Regulations Approved Document B.