An explosion is the sudden chemical reaction of a flammable substance with oxygen with the simultaneous release of high energy. Flammable substances may be present in the form of gases, vapors, mists or dusts. Explosion can only occur, when three factors come together:
1. Flammable material (in ignitable quantities)
2. Oxygen (in the air)
3. Ignition source
Classification flammable liquids:
The flash point of a flammable liquid is the minimum temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid.
·  If the flash point of a flammable liquid is well above the maximum temperatures that arise, an explosive atmosphere cannot be formed. The flash point of a mixture of various liquids may be lower than that of the individual components.
In addition to the boiling point, the flash point of a liquid serves to classify liquids as highly flammable, easily flammable and flammable liquids.
Explosive Limits:

To form an explosive atmosphere, the flammable substance must be present in a certain concentration.

If the concentration is too high (rich mixture) or too low (lean mixture), no explosion occurs. Instead, there is just a steady-state combustion reaction or none at all. It is only in the range between the lower and upper explosion limit that the mixture reacts explosively when ignited.

The explosion limits depend on the ambient pressure and the proportion of oxygen in the air.
Explosion Protection:

Preventing the formation of explosive atmospheres by
Ø  Avoiding flammable substances (replacement technologies)
Ø  Inserting (addition of nitrogen, carbon dioxide etc.)
Ø  Limitation of the concentration by means of natural or technical ventilation

Avoiding ignition of explosive atmospheres by
Ø  Following Anti Static Measures
Ø  Installation of Electrical equipment based on Zones
Ø  Avoiding all the spark generating activities

Mitigation of the explosion effects by
Ø  explosion pressure resistant construction
Ø  explosion relief devices

Ø  explosion suppression by means of extinguishers

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