Medium-Frequency Signal Propagation Characteristics of a Lifeline as a Transmission Line in Underground Coal Mines

Underground coal mines in the United States of America are required to install lifeline (LL) cable inside escapeways to guide miners out of a mine when visibility becomes poor due to heavy smoke. Some LLs consist of single or multiple steel conductors covered with a protective plastic outer layer. Research has shown that this type of LL can be a good conductor to guide a medium-frequency (MF) communication system signal to travel over large distances. To understand the MF propagation characteristics of an LL, National Institute for Occupational Safety and Health researchers took measurements on a section of LL in a coal mine, and obtained propagation parameters for analysis. The measurement data show that MF signals have a low attenuation which can enable the use of an LL for communication throughout a mine. The propagation parameters measured are presented in this paper.