In many industry secotors, you work in enviroments with gas, vapour, mist or dust; in others, flammable substances are used during the process. To avoid any danger, the ATEX products were designed. If these substances are mixed with the air and come into contact with an ingnition source, there is explosion risk.
Intrinsic safety devices indicate that the circuit energy is so low that the cannot be flammable by any fuel mix due to sparks or the device surface temperature.