Introduction to Fire Safety Management

Introduction to Fire Safety Management
➤ The amount of explosive atmosphere suffi cient to
cause injury or damage by ignition.
The consequences of both gas and dust explosions
will depend upon the environment in which the mixture
(dust or gas cloud) is contained or, in the case of the
gas cloud, what it engulfs. A gas explosion will be classifi
ed in relation to the environment in which the explosion
takes place, for example confi ned gas explosions
which occur within vessels, pipes, tunnels or channels,
or unconfi ned gas explosions commonly referred to as
unconfi ned vapour cloud explosions, which occur in
process plants and other unconfi ned areas.
Once the determination of the explosive atmosphere
has been established it is then necessary to consider
Figure 7.29 Primary and secondary explosions
130
Release of Gas
and/or Liquid
Blast wave
Primary Explosion
Dust cloud formed
Lying Dust
No Ignition
Immediate
Ignition
Formation of
Combustible
Fuel-Air
Cloud
(Premixed)
whether there is a presence of an ignition source which
will precipitate an explosion; such ignition sources
could be:
➤ Hot surfaces
➤ Naked fl ames and other hot gases
➤ Mechanically generated sparks
➤ Electrical equipment
➤ Static electricity
➤ Lightning
➤ Radio frequency (RF) – electromagnetic waves
➤ Ionising radiation.
Once ignited an explosion may have secondary repercussions,
particularly in the case of dust explosions. This
Figure 7.30 Diagram depicting typical consequences of the release of combustible gas into the atmosphere
Fire
Ignition
(delayed)
Heat from Primary Explosion lgnites Dust Cloud
Secondary Explosion
Gas
Explosion
No damage
Damage to
Personnel
and Material
Fire
Fire
and
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