Civil Engineering Reference
In-Depth Information
Fire
Chapter 1.8
Passive fire protection measures are
those features of the fabric, such as
compartment walls, that are
incorporated into building design to
ensure an acceptable level of safety.
These features are dealt with in outline
in this topic. Measures
which are brought into action on
the occurrence of a fire, such as fire
detectors, sprinklers, automatic
shutters and smoke extraction systems
are referred to as active
fire protection, and are not dealt with
here.
This chapter makes specific
reference to guidance for England and
Wales contained in Approved
Document B
(52)
as it affects walls,
windows and doors, but not to the
mandatory requirements for Scotland
which are contained in Part D for
structural fire precautions and Part E
for means of escape, made under the
Building Standards (Scotland)
Regulations 1990
(53)
, nor to those for
Northern Ireland in Technical Booklet
E made under the
Building
Regulations (Northern Ireland) 1994
(54)
. These requirements are different,
though no less stringent, and reference
should be made to the documents
themselves. Until 1986, inner London
had its own requirements which could
be traced back to the Great Fire of
London in 1666. One example is that
certain buildings covered by Section
20 of the London Building Acts, every
partition had to be fire resisting.
Although building regulations are
not retrospective, it may sometimes be
necessary in rehabilitation work to
review former provisions for the
fabric to determine its current
relevance.
The development of structural fire
protection
In medieval times, ecclesiastical and
military buildings had walls of stone,
which offered good resistance to fire.
The external walls of dwellings were
frequently of wattle and daub, which
offered reasonable resistance to fire.
However, the practice of jettying the
external walls meant that the upper
storeys of houses facing each other
across the street were often so close
together that fire could cross the gap
with relative ease, and legislation was
introduced to reduce the overhangs
and so to reduce the risk of fire
spreading.
Concern was not limited to external
walls; for example separating walls in
the late twelfth century in London
were specified to be 3 feet thick. The
most stringent requirements were, of
course, introduced after the Great
Fire
(55)
.
Even so, fires still occur with
distressing frequency, even in the
most highly monitored of buildings
(Figure 1.53).
●
to minimise the spread of fire, both
within the building and to nearby
buildings
to reduce the number of outbreaks
of fire
●
Relevant practical aims arising from
the second of these objectives are to
limit the size of the fire by:
●
controlling fire growth and spread
●
dividing large buildings, where
practicable, into smaller spaces
Fire resistance
The performance of a wall as an
element of structure can be judged on
its ability to satisfy specified criteria
for a given test duration. Examples
relevant to particular applications are
contained, for example, in Approved
Document B of the Building
Regulations for England and Wales.
It is not proposed to repeat here all
the relevant criteria from the
Approved Document - suffice it to
say that different criteria apply
according to, for example, a building
type, its height, and the relative
The objectives of fire precautions
The designer of a building or of
alterations to a building, whether new
or refurbished, will need to know a
great deal about the conditions that
will be imposed on walls within that
building in service. Factors such as
loading, environment and durability
all have to be understood and
assimilated into the design process,
and considered in relation to
behaviour in fire.
The objectives of fire precautions
include:
●
Figure 1.53
St George's Hall, Windsor Castle, after the
fire of 1992
to provide adequate facilities for
the escape of occupants
