Civil Engineering Reference
In-Depth Information
Supressor
Pressure rise
detector
Nozzle
Pressure wave
Pressure wave
Ignition
Flame
Figure 7.32
Explosion suppression system in operation
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.
EX
Figure 7.33
Warning sign for places where explosive
atmospheres may exist
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,
Table 7.4
Showing the zones for gases and vapours
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.
Note:
This zone can include, among others, places surrounding zones 0 or 1.
