Civil Engineering Reference
In-Depth Information
Roof covering:
•
Non-combustible
•
FR
•
Limited openings
External walls:
•
Non-combustible
•
FR
•
Limited openings
Adequate separation
Notional boundary
Figure 9.20
Preventing external fi re spread
depend upon the space separation between the roof
and any boundary likely to present a risk.
Fire resistance
- the degree of fi re resistance of
the external building will vary with the size and purpose
group of the building but as a minimum will normally
provide fi re resistance for at least 1 hour.
9.5
Means of escape
Unprotected areas
To prevent fi re spread by radiation from one building
to another, there would be no openings in the exposed
face of the building. This would of course be impracti-
cal; however, the openings in external walls that present
a risk to adjacent properties must be limited. Limiting the
size of any openings has the effect of limiting the size
of any source of radiated heat that may come from that
opening. For example, a large opening will allow a large
amount of fl ame to develop outside the opening which
will in turn radiate large qualities of heat. The smaller the
opening, the less the fl ame, the smaller the amount of
radiated heat.
Means of escape is defi ned by the Approved Document
as a 'structural means whereby a safe route is provided
for persons to escape in case of fi re, from any point in a
building to a place of safety, clear of the building, without
outside assistance'.
This defi nition provides a basis for solutions to
fi re safety planning in buildings and other structures.
However, there are a few prescriptive rules governing the
provision of the means of escape in particular situations.
It is useful to bear in mind that the means of escape
provision varies from building to building depending
upon such factors as the nature and size of the building
or structure, the use of the building and the nature and
disposition of the occupants. For example, the means of
escape in a traditionally built multi-storey hotel will need
to be of a far higher standard than the means of escape
from a single storey offi ce.
When considering what standard of means of escape
may be appropriate in a given situation it is necessary to
consider the factors relating to the:
The combustibility of roof coverings
Any surface that is pitched at an angle of less than 70º
from the horizontal should be considered as a roof. The
most signifi cant risk of fi re spread via the roofs of build-
ings is not only radiated heat but also fl ying embers
of burning material settling on the roof. It is important
therefore that the roof covering offers an appropri-
ate degree of fi re resistance. As with the construction
of external walls the amount of fi re resistance and the
amount of unprotected openings (e.g. roof lights) will
➤
Evacuation time
➤
Evacuation procedures
➤
Occupancy
