Explosive atmosphere hazard
Explosive atmospheres
A potentially explosive atmosphere is said to exist when an environment contains a mixture of air and flammable substances, in the form of gas, vapor, mist, dust or fibers in the right ratio. A specific definition of "explosive atmosphere" is given in the European explosion hazard directive: "an explosive atmosphere is an atmosphere in which after ignition combustion extends itself to the entire non-combusted mixture".
This is based on atmospheric conditions that can occur under normal circumstances in Europe:
- an ambient temperature of –20 °C to +60 °C;
- an air pressure of 0.8 to 1.1 Bar (80 to 110 kPa);
- air with an oxygen content of 21%.
Fig. 1.1 Fire or explosion triangle
If the explosive atmosphere contains an ignition source, a very dangerous situation occurs, which is shown in the explosion triangle above; all ingredients are present to cause an explosion or blast. Of course, fuel and oxygen (air) must be present in the correct ratio. Furthermore, the ignition source must also contain sufficient energy to ignite the mixture.
An explosion is characterized by a very sudden rise in pressure and temperature caused by oxidation (combustion) or another exothermic reaction. Bystanders and employees are at great risk because of the effects of flames, heat radiation, pressure waves, flying debris, harmful reaction products and the consumption of the oxygen required for people from breathing air.
Explosions can be subdivided into gas and dust explosions based on the type of fuel. The following types of fuels can be distinguished:
- Flammable gases (natural gas, hydrogen, etc.);
- Flammable vapors and mists of liquids (acetone, white spirit, etc.);
- Flammable solids and fibers (flour, sugar, wood dust, etc.).
Other types of explosions are also possible, such as physical explosions (a bursting balloon or bicycle tire) or explosions by explosives or ammunition. These fall outside the scope of the ATEX Directive.
Some important fuel properties will be explained in the following paragraphs.
