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The objective of this study was to develop a laboratory-scale method to rank the ignition and fire hazards of commonly used underground mine materials and to eliminate the need for the expensive large-scale tests that are currently being used. A radiant-panel apparatus was used to determine the materials’ relevant thermal characteristics: time to ignition, critical heat flux for ignition, heat of gasification, and mass-loss rate. Three thermal parameters, TRP, TP1 and TP4, were derived from the data, then developed and subsequently used to rank the combined ignition and fire hazards of the combustible materials from low hazard to high hazard. The results compared favorably with the thermal and ignition hazards of similar materials reported in the literature and support this approach as a simpler one for quantifying these combustible hazards.
In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a two-part heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation.
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 inmine 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. 2 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.
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