"Eight coal mines were visited to determine their communications usage and requirements. Presently available equipment was surveyed and evaluated to determine its applicability to the needs of the mines. The requirements, as determined from the surveys, and the capabilities, as determined from analysis and experiments, were summarized. Volume 3 contains all information used in predicting the performance of low-frequency transmissions in through-the-earth systems, along with the predictions themselves for typical situations." - NIOSHTIC-2 NIOSHTIC no. 10001395 523-0 765829-00 12 7 M

National Institute for Occupational Safety and Health