Civil Engineering Reference
In-Depth Information
and the relevant fl oor areas are:
600 m
2
(a) shop fl oor - 20 m
30 m
64 m
2
(b) offi ces - 8 m
4 m
32
2
(c) canteen - 8 m 10 m 80 m
2
.
This is the
total
fl oor area - not the usable fl oor area. It is
therefore necessary now to deduct the fl oor area of the
permanent features in the area where they are situated,
i.e.:
(a) WC in shop - 10 m
2
(b) Stairs in shop - 15 m
2
30 m
2
2
(c) WC in canteen - 10 m
2
.
Therefore, the total theoretical number of people for
which escape routes must be designed is:
560
2
(a)
Shop
280
64
6
(b)
Offices
11
70
1
(c)
Canteen
70
Figure 9.25
A room with a fi nal exit to an unenclosed
area outside
Total
361 people
in others for the purposes of assessing the adequacy of
the means of escape, the travel distances from all rooms
must be considered.
In some cases it will be possible to escape directly
from a room where a fi re may start to a fi nal exit to a
place of ultimate safety which will normally be an open
area in the open air. In these cases the only distance
that is relative is the distance within the room.
Stages of travel
- in most building designs it is
neither practical nor desirable to have fi nal exits from all
the rooms where a fi re may start. For most situations it
is necessary to consider the process of escape in four
distinct 'stages'
:
The number, width and disposition of exits can then be
provided and should be designed to allow 361 people to
escape within the required time.
As an alternative to calculating a theoretical number
is it perfectly acceptable to use real data from real
situations. In this case the data that is used to determine
the requirements of the means of escape should be
based on the highest average occupancy density.
9.5.3 Travel distances
Having fi rst considered the physical state and reactions
of the occupants and how these can be related to build-
ing type, it is important to look at the process of escape
and the maximum distances people can be expected to
travel to escape from fi re.
Obviously the distances people travel to get to safety
has a direct bearing on the time taken to evacuate in
the case of fi re. It is important to remember that travel
distances will vary depending upon the type of building,
the use of the building and the occupancy of the building.
Two crucial notions to help understand and assess
travel distances are that of a 'room of origin' and a 'fi nal
exit'. The room of origin is the term applied to the room
where a fi re may break out. For all buildings, all rooms
may be considered as rooms of origin and although the
likelihood of a fi re occurring in some rooms is greater than
Stage 1:
escape from the room or area of
fi re origin
Stage 2:
escape from the compartment of
origin via the circulation route to a
fi nal exit / entry to a protected stair-
way / to an adjoining compartment
offering refuge
Stage 3:
escape from the fl oor of origin to
the ground level
Stage 4:
fi nal escape at ground level.
