Dynatec/Middle Tennessee Zinc The MTZ mines utilize random room-and-pillar mining method that results in complex ventilation networks. Upon decommissioning, the mechanical ventilation units were removed and disposed of and several shafts sealed. In an effort to re-open the mines and operate in compliance with the Mine Safety Health and Administration (MSHA) diesel particulate matter (DPM) regulation of 160 µg/m3, a new ventilation system was required. The new ventilation system was developed based on the number of diesel equipment required to meet production. Particular emphasis was placed on the DPM, main fan sizing, and locations to enable the mines to meet MSHA’s ventilation requirements.