Hazard

CategoryArea
(m²)Occupancy
(see also
Appendix 3)Group 1
Group 2
Group 3
Group 4
Group 5/1
Group 5/2
Group 5/3
Group 5/43.0 x 3.0m
4.5 x 4.5m
6.0 x 6.0m
9.0 x 9.0m
3.0 x 3.0m
4.5 x 4.5m
6.0 x 6.0m
9.0 x 9.0m12m
18m
24m
36m
12m
18m
24m
36m9
20
36
81
9
20
36
81Breweries
Bakeries
Cotton Mills
Paint Manuf’ring
Electrical W’house
Pharmaceutical W’hse
Paper Storage W’hse
Plastic Foam W’hous

Fire Size Perimeter Approx
Examples of

In unsprinklered premises there is the possibility that, in
the absence of effective suppression (eg. sprinklers), the
fire may grow unchecked and eventually destroy the building.
In this instance the detection of the fire is paramount, and
human detection should not be relied upon. Hence a fire/smoke
detection system is recommended to:
(a) raise the alarm both within the building and with the
fire brigade;
(b) initiate the operation of the venting system
The fire may then develop if unchecked to a size at fire
service intervention which will be dependent upon:
(i) the nature of the goods, ie.
combustibility, burning.rate, radiation
output, etc;
(ii) the disposition of the burning material
with respect to other combustibles;
(iii) the geometry of the building
(eg. ceiling height etc);
(iv) the attendance and deployment time of the
fire service
An assessment of the largest likely fire size that the fire
service will encounter should be based upon the above
variables. In the absence of sufficient information or other
guidance being available (eg. British Standards), it is
suggested that the fire size for an unsprinklered fire be
taken as being twice the area of its sprinklered counterpart,
eg. a fire in a Group 3 hazard should be taken as 70m² area
(8.5m x 8.5m). An upper limit of around l00m² (lOm x lOm) may
be considered as an arbitrary maximum beyond which the venting
system will produce no further tangible benefit, other than to
assist fire-fighting operations.
Fire sizes outside these are not normally considered, and in no
circumstances should the design fire size for an unsprinklered
fire be less than that for a sprinklered fire of the same
hazard rating.