Terminologies
► Vapour Cloud Explosion: An explosion
occurring outdoors beginning with the unplanned release of a large quantity of
flammable gas or vapourising liquid which ignites following the formation of a
cloud or plume of pre-mixed fuel and air. The speed of flame travelling through
the cloud may approach detonation velocity
► Unconfined Vapor Cloud Explosion (UVCE): When
a flammable vapor is released, its mixture with air will form a flammable vapor
cloud. If ignited, the flame speed may accelerate to high velocities and
produce significant blast overpressure.
► Flash Fire: Flash fire is a sudden, intense
fire caused by ignition of a mixture of air and a dispersed flammable substance
such as a solid (including dust), flammable or combustible liquid (such as an aerosol
or fine mist), or a flammable gas. It is a fire that spreads with unusual
speed, as one that races over flammable liquid or through combustible gases
► A pool fire is a turbulent diffusion fire
burning above a horizontal pool of vaporising hydrocarbon fuel where the fuel
has zero or low initial momentum. Fires in the open will be well ventilated
(fuel- controlled), but fires within enclosures may become under-ventilated
(ventilation-controlled). Pool fires may be static (e.g. where the pool is
contained) or 'running' fires.
Consequences
► The possible consequences of an emergency
situation could be any one of the following or combination depending on the
characteristics/properties of the chemical involved & the type &extent
of the disaster that has occurred.
► Toxic emissions eg: if caused by leakage of
pipeline/flanges would result in release of emissions within the premises ,or
even beyond the premises, can cause flammable explosion(depending on its flammability)
or confined or unconfined vapour cloud explosion.
► In case of rupturee of a storage tank, discharge
of the hazardous substance may cause a pool of fire with or without a BLEVE
BLEVE: Boiling Liquid Expanding Vapour
Explosion refers to the sudden rupture (due to fire impingement) of a vessel
/systemcontaining liquified flammable gas under pressure. This immediate ignition
of the expanding fuel –air mixture leads to intense combustion creating a
fireball, blast wave & potential missile damage
CONSEQUENCE:
The expected physical result of
an incident (eg: gas or liquid release, fire explosion, overpressuring of
vessel, discharge of contaminant into a water way) can cause harm to people,
property and the environment (eg: heat radiation, explosion, overpressure,
concentration of toxic gas, contamination of habitat).
An incident is a deviation from the intended
operating conditions at a hazardous facility that has the potential to result
in an emergency (eg: hole in pipe work or vessel, runaway reaction, overfilling
of pressure vessel)
The triggerring of secondary events (such as
toxic releases) by a primary event (such as an explosion) such that the result
is an increase in consequence or in the area of an impact zone.
The forth coming slides are pictorial
representations of the various events /consequences….of a toxic release for 8
minutes which has led to disastrous consequences.
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