By primary explosion prevention are understood all the measures which prevent a potentially explosive atmosphere from occurring.
Here for example it is possible to replace a potentially explosive material by another with no danger of explosion, (e.g.: replace paints containing solvents by water-based paints).
Furthermore, the materials can be isolated, i.e.: to prevent the admission of air and thus of oxygen.
If it is not possible to prevent a potentially explosive atmosphere, then measures must be taken which prevent ignition of the potentially explosive atmosphere.
By avoiding sources of ignition, once again one of the conditions of the explosion triangle is removed. Thus an explosion cannot occur.
In the Workplace Directive 99/92/EC, or alternatively in IEC Standard 60079-10, all potentially explosive areas are to be divided into zones by the plant operator. The higher and longer the probability of the occurrence of a dangerous, potentially explosive atmosphere is, the more demanding the requirements on the devices in use are. In the zones, the probable effectiveness of sources of ignition must be prevented.
The following examples could be considered possible sources of ignition: Cf: DIN EN 1127-1, draft April 2009
If it is not possible to ensure that the occurrence of a potentially explosive atmosphere is prevented, and if it is not possible to exclude its ignition, then additional explosion prevention measures must be applied. The objective is to control or limit the effects of an explosion.
Tertiary explosion prevention is thus applied when the measures of primary and secondary explosion prevention are not sufficient.
This can be carried out for example by means of the following measures: