Introduction to Health and Safety at Work

13.12.3 Surface spread of fi re
Combustible materials, when present in a building as 
large continuous areas, such as for lining walls and ceil-
ings, readily ignite and contribute to spread of fi re over 
their surfaces. This can represent a risk to life in build-
ings, particularly where walls of fi re escape routes and 
stairways are lined with materials of this nature.
Materials are tested by insurance bodies and fi re 
research establishments. The purpose of the tests is to 
classify materials according to the tendency for fl ame to 
spread over their surfaces. As with all standardized test 
methods, care must be taken when applying test results 
to real applications.
Figure 13.10
Steel structures will collapse in the heat of 
a fi re.

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Introduction to Health and Safety at Work
218
In the UK, a material is classifi ed as having a surface 
in one of the following categories:
➤
Class 1 – Surface of very low fl ame spread
➤
Class 2 – Surface of low fl ame spread
➤
Class 3 – Surface of medium fl ame spread
➤
Class 4 – Surface of rapid fl ame spread.
The test shows how a material would behave in the ini-
tial stages of a fi re.
As all materials tested are combustible, in a serious 
fi re they would burn or be consumed. Therefore, there 
is an additional Class 0 of materials which are noncom-
bustible throughout or, under specifi ed conditions, non-
combustible on one face and combustible on the other. 
The spread of fl ame rating of the combined Class 0 
product must not be worse than Class 1.
Internal partitions of walls and ceilings should be 
Class 0 materials wherever possible and must not exceed 
Class 1.
13.12.4 Fire resistance of structural elements
If elements of construction such as walls, fl oors, 
beams, columns and doors are to provide effective bar-
riers to fi re spread and to contribute to the stability of 
a building, they should be of a required standard of fi re 
resistance.
In the UK, tests for fi re resistance are made on 
elements of structure, full size if possible, or on a 
representative portion having minimum dimensions of 
3 m long for columns and beams and 1 m
2
for walls and 
fl oors. All elements are exposed to the same standard fi re 
provided by furnaces in which the temperature increases 
with time at a set rate. The conditions of exposure are 
appropriate to the element tested. Freestanding columns 
are subjected to heat all round, and walls and fl oors are 
exposed to heat on one side only. Elements of structure 
are graded by the length of time they continue to meet 
three criteria:
➤
the element must not collapse
➤
the element must not develop cracks through which 
fl ames or hot gases can pass
➤
the element must have enough resistance to the 
passage of heat so the temperature of the unex-
posed face does not rise by more than a prescribed 
amount.
The term fi re resistance has a precise meaning. It should 
not be applied to such properties of materials as resist-
ance to ignition or resistance to fl ame propagation. For 
example, steel has a high resistance to ignition and 
fl ame propagation but will distort quickly in a fi re and 
allow the structure to collapse – it therefore has poor 
‘Fire Resistance’. It must be insulated to provide good 
fi re protection. This is normally done by encasing steel 
frames in concrete.
In the past, asbestos has been made into a paste 
and plastered onto steel frames, giving excellent fi re 
protection, but it has caused major health problems and 
its use in new work is banned.
Building materials with high fi re resistance are, for 
example, brick, stone, concrete, very heavy timbers (the 
outside chars and insulates the inside of the timber), and 
some specially made composite materials used for fi re 
doors.