a safety circuit permits the operation of a device when the device is located in a safe operating environment . there is a power supply that supplies power to the sensor and to the logic circuits . the sensor could be one of any number of sensors depending on the environment variable which it is desired to detect or monitor and the size of the space for the detector to fit in . the logic circuits use the signal from the sensor to determine when a safe condition exists . when the logic circuits determine that a safe environment is present , the logic circuits send a signal to the power control circuit , which will permit the operation of the device , which if operated in an unsafe environment could endanger personnel and / or property . the results of operating a device in an unsafe environment could include , but are not limited to , fire ; explosion ; injury or death of personnel , or any other undesirable event .