Mining Project: Improving Mine Ventilation and Reducing Contaminant Exposure in Large-Opening Stone Mines

Research Summary

Underground workers in large-opening stone mines may be exposed to respirable crystalline silica (RCS) and diesel particulate matter (DPM) at levels above the regulatory limits set by the Mine Safety and Health Administration (MSHA). New research and engineering solutions are lacking for these mines which can improve the ventilation and reduce contaminant exposure.

Underground stone mine ventilation comes with a specialized set of challenges because of the large size of underground openings. There are three main ventilation problems in limestone mines. First, moving adequate ventilation airflow volumes can take many hours. The total open-space volume in a typical large-opening mine can be enormous (~250 million cubic feet), and fans capable of moving 1,000,000 cubic feet per minute take many hours to complete an air change. The amount of open space often results in these operations having stagnant air, fog, and high DPM and dust concentrations. Second, controlling and directing airflow in these operations is through momentum rather than differential pressure, due to the low ventilation pressures encountered. In addition, stoppings in large-opening operations are expensive to build and difficult to maintain due to blast pressures generated during production. The third issue is ventilation system planning. As the operation grows, managers typically work multiple face areas along the perimeter of the mine and, consequently, maintaining a ventilation system is complicated by the use of multiple booster/auxiliary fans, main fans, and natural ventilation being in the mix.

With mines going deeper with multiple levels, planning a ventilation system is becoming even more challenging. In addition to the technical challenges, most stone mines lack mine ventilation expertise. Such operations usually have just one or two mining engineers on staff who are responsible for all of the engineering, operations, planning, and management aspects of the mine. For the reasons above, having an adequate and effective ventilation system is challenging for the nation’s large-opening stone mines.

In this project, the above issues will be addressed by way of five research aims, as follows:

1. To conduct field studies on the use of long stone pillars, alternative mine layouts, innovative stopping designs, and fan types/placements for removing airborne contaminants by more efficient direction of ventilation airflows.
2. To conduct field studies and gather relevant data on the presence of RCS and DPM in critical areas of large-opening mines.
3. To develop computational fluid dynamics (CFD) models to simulate and remediate airflow issues in large-opening mines and to investigate the application of an air filtration system for mitigation of dust exposures on working faces and dead-end entries.
4. To develop an updated mobile application version (iOS and Android) of the AQE (Air Quantity Estimator) software for estimating airflow requirements to adequately dilute DPM in underground workings.
5. To develop guidelines to create maximum ventilation efficiencies in large-opening stone mines and to disseminate findings through development of a practical ventilation design handbook for mine operators.

The projected impacts of this project research are that large-opening mine operators will incorporate NIOSH recommendations, work practices, and interventions for improvement of ventilation and reduction of overexposures to RCS and DPM. Secondly, fan and equipment manufacturers will integrate recommendations on air filtration systems into their designs to reduce contaminant exposures in large-opening mines. Finally, NIOSH-developed software tools and mobile applications will be adopted by mine operators to estimate the air quantity requirements in their mines based on diesel equipment use underground.