Mining Publication: Review of Rock Dusting Practices in Underground Coal Mines

Proper rock dusting practices have proven to be an effective means of preventing coal dust explosions. Rock dust (generally pulverized limestone dust) serves as a heat sink material that prevents or suppresses a propagating coal dust explosion through the absorption of thermal energy from the heated gases and absorption of radiant energy, which reduces the preheating of unburned coal particles ahead of the flame front. Therefore to effectively suppress a coal dust explosion, sufficient quantities of dispersible rock dust must be entrained into the mine entry by the expanding explosion pressure wave to inert the coal dust, also entrained in the entry. The in-mine application of rock dust dates back to the early 1900s. Since that time, significant technological improvements to rock dust application methods have been implemented along with increasingly stringent regulatory requirements and inspections to ensure adequate quantities of rock dust are applied to the roof, ribs, and floor throughout the mine. Even with enhancements to the rock dusting application methods and equipment, coal mining operations still experience compliance issues associated with meeting the current total incombustible content (TIC) requirement of at least 80% for all mine dust samples.

The National Institute for Occupational Safety and Health (NIOSH) conducted general surveys of rock dusting practices at nine underground coal mining operations and met with Mine Safety and Health Administration (MSHA) mine inspectors and District personnel to gain a better understanding of the rock dusting practices and associated compliance issues during this survey period. These surveys included obtaining the following from each of the nine mines:

• Mine dust samples to assess the incombustible content (IC) for determining any rock dust deficient areas common to all nine mines,
• Information and issues related to rock dusting, and
• Rock dusting sampling practices.

This report discusses research that was conducted in the NIOSH laboratories, experimental mine, and in operating mines to evaluate the potential explosion hazard associated with excessive coal dust accumulating on elevated surfaces, the efficacy of wet rock dusting, and the need for mines to develop comprehensive rock dusting programs. Taken as a whole, this report provides proactive approaches to current rock dusting practices that will improve the application of rock dust in all underground areas of a coal mine.