Introduction to Fire Safety Management

Principles of fi re and explosion
133
The trigger of such a suppression system is likely to 
be via either a pressure sensor or fl ame sensor, each will 
have systems to prevent false alarms and actuation.
In addition to a suppression system an alterna-
tive may be control by the addition of a liquid; however, 
there are environmental implications where water and 
dust residues have the potential to contaminate the 
environment.
Housekeeping in relation to the removal of dust 
accumulations must be considered although as previously 
discussed this should be undertaken with careful con 
-
sideration to eliminate the possibility of secondary dust 
explosions. Installing good dust extraction systems 
and making arrangements for spilt dust to be removed 
immediately using vacuum systems or explosion-proof 
vacuum cleaners will assist in the management of dust 
control; however, those operated by individuals rely 
heavily upon human factors and the level of competence, 
training and instruction.
Ultimately, as is the case with all hierarchies of control 
the provision of suitable personal protective equipment 
may be considered.
Plant layout and classifi cation of zones
Any building or plant where there is the potential for gas-
eous or dust explosions must be designed upon simi-
lar lines to those in which explosives are manufactured, 
EX
Figure 7.33
Warning sign for places where explosive 
atmospheres may exist
Figure 7.32
Explosion suppression system in operation
Supressor
Pressure rise
detector
Pressure wave
Nozzle
Ignition
Pressure wave
Flame
Zones for gases/vapours
Zone 0 
A place in which an explosive atmosphere consisting of a mixture with air of fl ammable substances in the form of 
gas, vapour or mist is present continuously or for long periods or frequently.
Note:
In general these conditions, when they occur, arise inside containers, pipes and vessels, etc.
Zone 1 
A place in which an explosive atmosphere consisting of a mixture with air of fl ammable substances in the form of 
gas, vapour or mist is likely to occur in normal operation occasionally.
Note:
This zone can include, among others, the immediate vicinity:
➤
Of zone 0
➤
Of feed openings
➤
Around fi lling and emptying openings
➤
Around fragile equipment, protective systems, and components made of glass, ceramics and the like
➤
Around inadequately sealed glands, for example on pumps and valves with stuffi ng-boxes.
Zone 2 
A place in which an explosive atmosphere consisting of a mixture with air of fl ammable substances in the form of 
gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.