Civil Engineering Reference
In-Depth Information
inter-mediate standard but small rooms may be to
the lower standard of Class 3 classifi cation due to the
shorter travel distances.
Table 9.4 summaries the Building Regulations'
requirements for the use of the various classes in a
number of locations.
fi re spread is aided by fl ying embers of burning material
being blown from the fi re onto surrounding buildings.
For all buildings that are built within 1 m of the
boundary to the property, fl ame spread is the main
mechanism. Beyond this distance, the mechanism for
fi re spread is assumed to be radiation. Fire spread from
building to building by radiation is dependent upon the:
➤
Size and intensity of the fi re
➤
Distance between and building on fi re and any
neighbouring structures
Table 9.4
Classifi cation of surface linings
Location
National
➤
Extent of the building surface capable of transmit-
ting heat.
class*
Small room - area not more than:
3
4 m
2
in residential buildings
30 m
2
in non-residential buildings
The risk of fi re spread by radiation is affected by a
number of factors relating to space separation between
buildings, the construction of the external walls and the
combustibility of roof coverings.
Domestic garages - area not
greater than 40 m
2
Other rooms
1
Circulation spaces in dwellings
Other circulation spaces
0
Notes:
(i) Any material/product classifi ed as non-combustible when tested in ac-
cordance with the requirements of BS 476 Part 4:1970.
(ii) Any material which, when tested to BS 476 Part 11:1982, does not fl ame
or cause any rise in temperature on either the specimen or furnace ther-
mocouples.
(iii) Any material which is totally inorganic, such as concrete, fi red clay, ceram-
ics, metals, plaster and masonry containing not more than 1% by weight
or volume of organic material. Any material conforming to the above re-
quirements can be classifi ed as Class 0 in accordance with Approved
Document B of the England and Wales Building Regulations 2006.
* BS 476 Part 7:1987 details the method for classifi cation of the surface spread
of fl ame of products (and its predecessor BS 476 Part 7:1971). The test is a
classifi cation system based on the rate and extent of fl ame spread and classi-
fi es products 1, 2, 3 or 4 with Class 1 being the highest classifi cation.
Figure 9.19
External fi re spread
Space separation
When planning a building or assessing the fi re risk of an
existing building the distance between it and the next
nearest building should be calculated using the distance
to the boundary of the property. If this is not appropriate,
for example when two buildings are on the same site, a
'notional' boundary must be used which is normally half
the distance between the two buildings. Although there
may not actually be another building on that boundary
at the time of planning or assessment it allows consid-
eration of how much fi re resistance and/or unprotected
areas may be appropriate in the walls of the building
being considered.
9.4.7
Preventing external fi re spread
It is important that the potential spread of fi re from a
building to a neighbouring structure is restricted. The
fi rst attempts to limit the spread of fi re from one building
to another followed the Great Fire of London in 1666
when a small fi re in the city spread to disastrous propor-
tions due to the complete lack of fi re resistance or fi re
separation of buildings. Since that time it is a requirement
that buildings are constructed from non-combustible
material, have limited openings (such as windows) close
to adjacent buildings and have external surfaces that
are themselves resistant to radiated heat from adjacent
properties.
There are two ways that fi re can spread between
buildings, i.e. by the fl ames from a fi re in one building
directly impinging on an adjacent building or by radiated
heat from the building on fi re igniting the adjacent
building. Experience has shown that in both these cases
Construction of the external walls
The nature of the building materials and the numbers
of windows or other openings obviously affect both fi re
spreading to and from a building. It is therefore neces-
sary to ensure suffi cient fi re resistance of external walls
and to limit the amount of the surface area which is not
protected by fi re resistance.
