For an electrical product to be 'Intrinsically Safe' it must be incapable of igniting an explosive atmosphere by either spark or heat. This is achieved by ensuring only low currents and voltages enter the hazardous area, and therefore the whole circuit must be considered, not just the device in isolation.

An 'Intrinsically Safe Circuit' therefore must restrict the electrical and thermal energy such that ignition of a hazardous atmosphere (explosive gas or dust) cannot occur.