A term applied to any electrical circuit, wiring system, or apparatus that is not capable of generating an ignition-capable arc or ignition-capable heat under either normal or abnormal operation. Typically, such a circuit, wiring system, or apparatus operates at very low voltage and current levels.
Intrinsically-safe equipment is used in the sensing probes installed in underground gasoline storage tanks. These are electronic devices, capable of detecting minute changes in the liquid level in the tank.
Some can also detect the presence of water. However, the voltage and current capabilities used in these systems are so low that they cannot create a spark to ignite gasoline vapors in the tank. The equipment is thus said to be intrinsically safe.