The electrical energy available in circuits and equipment, is limited to a level to low to ignite the most easily ignitable mixtures in a hazardous area.Intrinsically safe barriers, as Zener, are installed in the circuit to limit current and voltage in the hazardous areas to avoid sparks or hot spots under fault conditions.
The principle of this type of the protection is that the apparatus to be protected is submerged in a suitable substance in liquid state which is then allowed to cool and form a solid block. This avoids direct contact between the electrical apparatus and the explosive atmosphere
Pressurized Apparatus (Purged Apparatus)
In this type of protection the pressure inside the enclosure housing the electrical equipment is maintained at a positive pressure (higher than atmospheric pressure outside enclosure) so as not to allow ingress of inflammable gas mixture thus avoiding possibility of explosion.