Mining Project: Improving Coal Dust Explosion Hazard Assessment Strategies

Research Summary

This project had six research aims, as follows:

1. Re-examine combustible dust assessment procedures used by the Mine Safety and Health Administration (MSHA) and the mining industry for their efficacy in view of modern mining practices.
2. Examine the impact of variations in rock dust properties and application practices and how these variations may influence inerting effectiveness.
3. Examine the efficacy of the Coal Dust Explosibility Meter (CDEM) as a compliance tool.
4. Ascertain the effectiveness of rock dust that is wetted, then dried, in suppressing coal dust explosions and recommend solutions to the caking issue.
5. Identify potential deficiencies in the current coal dust and rock dust definitions per 30 CFR 75.2.
6. Develop guidance for practices that effectively distribute rock dust using existing ventilation and rock dusting equipment.

Underground coal dust explosions are highly destructive and often result in a significant loss of life. A primary defense against such dust explosions is application of rock dust to inert accumulations of explosible coal dust. Although past work by NIOSH justified and subsequently resulted in an increase in the incombustible content requirements in all underground airways, problems continued to exist in the uniformity of rock dust sampling procedures, the adequacy of rock dust performance, and continuity of rock dust application.

This research effort developed empirically based recommendations for changes to the current combustible dust sampling protocols in U.S. underground coal mines. These protocols included assessments of sample spacing, roof and rib mesh influence, floor dust sampling depth, and use of the CDEM as a compliance tool. As a result, MSHA had revised the rock dust sampling policy and procedure in 2013 to reduce the depth of floor sample, to keep the roof/rib sample separate from the floor sample, and to revise the sampling locations within the entries. This research addressed deficiencies in the current rock dust definition by examining particle size distributions and inerting influences, the tendency for rock dust to form a cake when exposed to water, and an allowance for elevated levels of combustible matter in the rock dust. Anti-caking rock dusts have been developed and findings have been relayed to the rock dust industry through partnership meetings. Based on the research results, this work also suggested a tighter size distribution which includes a minimum surface area value to maintain inerting effectiveness. In the NIOSH IC Coal Dust Explosibility Meter Evaluation and Recommendations for Application, the CDEM was recommended as a compliance tool to allow real-time assessment of coal dust explosion hazards in underground coal mines for the prompt initiation of corrective actions.