This volume covers electromagnetic and seismic equipment for locating and communicating with workers trapped underground either behind barricades, in refuge chambers, or attempting to escape. The electromagnetic (em) voice downlink and coded beacon uplink were tested and qualitatively and quantitatively evaluated at five different coal mines. In the voice downlink test, intelligible voice transmission was received using a horizontal wire transmitting antenna terminated in the ground at each end. Coded beacon transmissions were also detectable on the surface. Studies indicate that the em system could be effectively used in rescue operation in most coal mines, provided that the mines were equipped with subsurface em transmitters and receivers. Further testing, however, was recommended including operation of the communications/location subsystem in a continuing training program.