Civil Engineering Reference
In-Depth Information
Consideration must also be given to those
people who work in remote parts of buildings such
as storerooms, boiler rooms or lift plant rooms. When
assessing the means of escape for the building a
competent assessor will ensure the escape arrangements
for all persons in the building are considered despite their
location throughout the building.
Distribution is clearly linked with the purpose
group and exact type of premises, e.g. factory, shop,
etc., and the nature and type of the occupancy of the
building.
Density factor
When planning the means of escape during design
(unoccupied premises), or for those with variable pop-
ulations such as places of public entertainment, it may
be diffi cult to calculate the maximum numbers who will
be present. In addition, there will be occasions when it
will be necessary to determine the maximum numbers
of people who should be allowed to occupy a particular
space in any particular purpose group.
In order to achieve a realistic calculation as to how
many may or should be occupying a certain space
reference must be made to 'density factors'. The density
factor may be defi ned as 'the available fl oor space per
person'. The Approved Document B provides numeric
values to assist in calculating how many persons may be
present (see Table 9.5). In order to calculate the density
factor for a particular building or area, it is necessary
to know:
Figure 9.23
The occupancy of sports stadium
provision of the means of escape thought must be given
to the following factors:
➤
Number of occupants
➤
Distribution
➤
Density.
Number of occupants
The number of occupants for an existing building with
a reasonably fi xed population may be ascertained by
questioning the responsible person who owns or occu-
pies the building. For buildings such as theatres or cin-
emas, the number of seats provided should be counted.
However, there are many buildings where it is necessary
to assume or estimate the total number of occupants.
It is important to consider the totals that may be
reasonably expected, for example in school halls although
the normal use may be for sports where small numbers
are present the space may also be used occasionally for
assemblies or fundraising social events where there may
be large numbers of pupils and/or parents attending.
➤
The use
➤
The fl oor space.
To assess the density factor, the
usable
fl oor space must
be calculated. The usable fl oor space
excludes perman-
ent features,
i.e. stairs, toilets, lifts, escalators, corridors
and other circulation spaces.
Consider the example in Figure 9.24.
Because the parts of the building are put to different
uses, it is necessary to use different density factors.
In order to calculate the number of people, it is fi rst
necessary to divide the fl oor area by the fl oor space
allowed per person, i.e.:
If density factors for Figure 9.24 are:
Distribution
The distribution of occupants within a building is also crit-
ical to the safety of occupants when assessing escape
routes. In addition to the total numbers of people who
may occupy a building, where those people are located
within the building has a signifi cant affect on the require-
ment for their means of escape. For example, the means
of escape from a retail premises situated at ground fl oor
level will be of a lesser standard than if the premises
were situated in a basement, or on the second fl oor of a
department store.
area of room or storey
floor s
No. of people
pace per person
(a) Shop fl oor (main sales) - 2 m
2
per person
(b) Offi ce - 6 m
2
per person
(c) Dining room and canteens - 1 m
2
per person
