NIOSH Mining Safety and Health Research

The underground extraction of mineral resources creates one of the most hazardous work environments in the Nation. Most mining accidents today generally involve only a few individuals. However, the infrequent occurrence of gas and/or dust explosions puts the lives of the entire underground workforce at risk. A total of 106 U.S. coal miners have been killed in 17 explosions since 1980. Four of these explosions resulted in more than 10 fatalities each. The most recent explosion, which occurred at the McElroy Mine in West Virginia in January 2003, resulted in three deaths and three injuries. The Jim Walter Resources No. 5 Mine explosion in Alabama in September 2001 resulted in 13 deaths. In July 2000, 2 miners were killed and another 12 injured at the Willow Creek Mine explosion in Utah.

Explosions can be prevented or mitigated by eliminating ignition sources, by minimizing methane concentrations and coal dust accumulations, by generalized rock dusting, and by using passive and active barriers to suppress propagating explosions. In addition to the hazards associated with flammable gas and combustible dust atmospheres, prolonged exposure to airborne contaminants such as coal dust and diesel emissions can result in adverse health effects. The concentration of methane and other airborne contaminants underground can generally be controlled by dilution (ventilation), capture before entering the host airstream (methane drainage), or isolation (seals and stoppings). The mission of the NIOSH Mine Ventilation and Explosion Program is to enhance worker health and safety in the mining industry by improving air quality and reducing explosion hazards through the development and implementation of scientific ventilation technologies and practices. The projects in this area include both basic and applied research with an emphasis on field-based research supported by lab experiments.

The project, "Reducing Airborne Contaminants in Large-Opening Mines," seeks to improve the ventilation in underground stone mines and other metal/nonmetal operations. Improving ventilation reduces workers´ exposure to airborne contaminants which include diesel emissions, silica dust, and toxic fumes from blasting. Delivering adequate quantities of fresh air to the mining working face areas is particularly challenging since these mines typically have entries characterized by cross-sectional areas over 1,000 sq ft. This project is developing new methods and equipment to optimize ventilation in large-opening mines. The use of large propeller fans to increase the total mine ventilation airflow has been demonstrated. Research continues on modified mine planning options using auxiliary fans, long stone pillars, and unit ventilation and improved stopping designs to increase the total mine ventilation efficiency. Software to estimate the ventilation air quantity necessary to dilute diesel emissions from a mine´s diesel vehicle fleet has been developed. These techniques to optimize ventilation under a variety of conditions are part of the project´s general goal to integrate ventilation into the mine planning process.

Basic and applied research into the causes and mechanisms of gas and dust explosions is part of the "Mine Explosion Prevention" project. This work is the basis for the development of techniques and strategies to prevent and suppress explosions. Large-scale coal dust and methane explosion studies at NIOSH´s Lake Lynn Experimental Mine (LLEM) are supported by small-scale lab tests. Current studies include measuring the size of coal dust in underground mines and determining (through LLEM tests) the amount of rock dust necessary to inert this size of coal. Post-explosion observations at the LLEM helps the Mine Safety and Health Administration (MSHA) in its forensic investigation of explosion accidents.

Methane is one of the most dangerous gases encountered in underground mining. In the cases of high-methane content coal, ventilation alone is sometimes not enough to sufficiently dilute these levels. In this case, coalbed degasification prior to mining and use of gob gas boreholes to drain methane from fractured strata above the mining panel are often required. However, the success of these techniques depends largely on the knowledge of borehole design and the behavior of methane reservoirs. The "Reservoir and Neuro-Simulation Control of Methane" project investigates analytical and numerical methods for predicting the behaviors of fractured reservoirs and the productivities of gob gas boreholes. During the project, surface and downhole gob gas boreholes are instrumented. The production data and strata permeability data, together with the corresponding geophysical logs and core analyses, characterize the fractured zones and are used to develop numerical reservoir models and artificial neural network based-models to predict borehole productivities. These models can produce the best borehole design to optimize methane management for varying mining conditions.

Longwall mining creates a complex underground environment that poses many problems in methane control. This includes multiple sources of gas and the necessity for an integrated use of multiple control strategies, including ventilation and methane drainage. Research under the "Control and Monitoring of Methane in Coal Mines" project determines airflow and methane emission patterns surrounding longwall faces and gobs to improve methane control systems. The complicated interaction of the main, tailgate, and bleeder ventilation systems is investigated to improve our understanding of methane flow paths. This modeling effort predicts the expected increases in gas emissions when extracting substantially larger longwall panels, a trend that the industry is currently following.

Longwall mining creates a complex underground environment that poses many problems in methane control. This includes multiple sources of gas and the necessity for an integrated use of multiple control strategies, including ventilation and methane drainage. Research under the "Control and Monitoring of Methane in Coal Mines" project determines airflow and methane emission patterns surrounding longwall faces and gobs to improve methane control systems. The complicated interaction of the main, tailgate, and bleeder ventilation systems is investigated to improve our understanding of methane flow paths. This modeling effort predicts the expected increases in gas emissions when extracting substantially larger longwall panels, a trend that the industry is currently following.

Improving design and safety of ventilation controls, practices, and monitoring are the aims of the project titled "Utilization of Belt Air in Underground Coal Mines." This research focuses on ways to reduce leakage through ventilation controls, to improve escapeway design, and to develop guidelines for using booster fans in underground coal mines. Leakage in large underground coal mines is often 50-60 % of total airflow and can lead to contamination of escapeways. In case of an underground fire, smoke should not reach any escapeways because of leakages through poorly constructed or deteriorated stoppings. Booster fans may offer a way to reduce leakage between the belt entry and the intake escapeway, but their use in this country is currently prohibited in underground coal mines. This research investigates the important issues of booster fan usage including permissibility and the advantages and disadvantages of fan operation in emergency situations.