Personnel safety sensing system

A location system for locating workers comprising:

• a plurality of light detectors mounted at known locations and configured to detect light from one or more workers;
• wearable devices to be worn by one or more of the workers who are authorized workers, the wearable device including a wireless transceiver;
• a plurality of wireless receivers mounted at known locations and configured to detect wireless signal transmissions from the wearable device;
• and
• a processing system configured to:
• determine locations of the workers using the light detected by the light detectors;
• determine locations of the authorized workers using the wireless signal transmissions from the wearable devices detected by the wireless receivers;
• compare the workers whose locations are determined using the light detected by the light detectors with the authorized workers whose locations are determined using the wireless signal transmission from the wearable devices detected by the wireless receivers;
• and
• based on the comparison, identify as unauthorized workers any workers whose location is determined using the light detected by the light detectors who are not authorized workers whose location is determined using the wireless signal transmissions from the wearable devices.