Preventing coal dust explosions

15 September 2011

Mine explosions remain a threat to underground coal miners, requiring constant vigilance to prevent accumulations of combustible gasses and dusts and to limit sources of ignition.

Coal Dust Explosibility Meter (CDEM)

Accumulations of combustible dust in coal mines create the risk of large-scale explosions that can result in multiple deaths and traumatic injuries. The explosion hazard can be effectively controlled through the application of rock dust, such as limestone dust, to render inert the combustible coal dust generated during the mining and transport of coal.
Traditionally, determining when additional rock dust should be applied or evaluating the effectiveness of existing rock dust application has been limited to a subjective visual evaluation or to the collection and laboratory analysis of dust samples, a process that requires days or weeks to identify a hazard.
For decades, miners have been able to monitor the concentrations of methane and other combustible gasses using handheld, direct reading gas detectors. These detectors have allowed miners to take immediate action to dilute gasses and prevent explosions.
With this same purpose in mind, researchers at the National Institute for Occupational Safety and Health (NIOSH) developed a real-time dust explosibility measuring instrument to provide instant feedback to miners on the relative hazard of dust accumulations in the mine and the effectiveness of their rock dusting practices. This instrument, the Coal Dust Explosibility Meter (CDEM), is a simple-to-use handheld device that provides a pass/fail assessment of coal mine dust samples.
With this device, miners, regulators and mine operators will have the information necessary to take immediate action to eliminate an explosion hazard.
Development of the CDEM required significant research1 by NIOSH's mine safety and health research programme and its predecessor programme in the US Bureau of Mines – in collaboration with the Mine Safety and Health Administration (MSHA) – to identify a technology that could provide real-time results comparable to the existing laboratory test.
Researchers then transferred the technology from a laboratory setting to a rugged hand held device and refined the device to pass the rigorous MSHA evaluation for intrinsic electrical safety.
In late 2010, NIOSH upgraded the device software to include ambient methane in the hazard determination and revised the calibration procedures to address issues identified in an earlier MSHA field study. In April of 2011, MSHA approved the CDEM for use in underground coal mines. Miners, mine operators and regulators will now be able to make real-time determinations of excessive coal dust accumulations and take immediate actions to prevent fatal mine explosions.