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Types of major chemical/industrial hazards - Explosion

An explosion involves the production of a pressure discontinuity or blast wave resulting from a rapid release of energy. A pressure disturbance is generated in to the surrounding medium. Air becomes heated due to its compressibility and this leads to an increase in the velocity of sound, causing the front of disturbance to steepen as it travels through the air. The loading and hence the damage to the nearby targets are governed by the magnitude of and duration of pressure waves. Missiles may be generated by an explosion and are capable of causing severe damage to adjacent plant structures and people.

The explosion mainly occurs due to the rapid combustion of a flammable material but can be brought about the chemical reactions other than combustion, provided they release large amount of energy (heat). Examples of these chemical reactions are Polymerizations, the decomposition of unstable substances and exothermic interactions of many kinds.

Classification of Explosions

  • Chemical Explosions
  • Physical Explosions
  • Vapour Cloud explosions

Chemical Explosion

Chemical explosions in plant or in vessel can arise due to exothermic reaction occurring internally. Such reaction may involve decomposition of unstable substances, polymerization of monomers, or combustion of fuel oxidant mixtures. Heating and increase of molecular number can result in a rise in pressure to the bursting point of the vessel, and explosives decompose so quickly that confinement and the development of pressure are self-imposed.

Physical Explosion

It occurs simply due to over pressure as in the case of steam boiler and air receiver explosions. Fire is not necessarily a consequence. But fire involving stock, buildings and plant ancillaries can cause physical explosions due to overheating followed by the overpressure in vessels and also the fireballs if contents are flammable. One such case is termed as Boiling Liquid Expanding Vapor Explosion (BLEVE). BELEVE is discussed in details, it happens in LPG/Propane storage facilities.
The effect of various heat radiation levels is given in the next Table.


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