Mining Contract: Sensors for Automated Control of Coal Dust (SACCD)

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

Underground coal mining operations produce finely divided coal dust (float dust) which can propagate an explosion. Limestone powder, known as rock dust, is widely used to inert coal dust to reduce explosion likelihood and to achieve compliance with mine safety regulations. To assist mine operators in monitoring the ratio of rock dust to coal dust on underground coal mine surfaces, NIOSH has developed the Float Dust Deposition Meter (FDDM) and the Coal Dust Explosibility Meter (CDEM). Building on these advances, improved methods that will address the problem of monitoring adequate rock dust coverage are now possible.

Under this contract, the University of California was tasked with developing small wireless sensors that can be deployed throughout the underground coal mine to monitor the coal and rock dust conditions. These devices would form an integrated wireless network that automatically measures the ratio of rock dust to coal dust and indicates when the ratio is below the explosibility threshold—i.e., when insufficient rock dust is present. This would result in small sensors that would require little manual labor once placed in the mine, be capable of continuously monitoring large areas in multiple locations, produce real-time data that can be used to automate rock dusting equipment, and trigger alarm conditions when necessary.

The contractor developed a sensor test fixture with the following basic components: (a) a deposition plate with a mass sensing resonator, including in-situ humidity and temperature sensors; (b) a light-emitting diode (LED); (c) light-sensing detectors; and (d) housing for the low-power radio and supporting electronics. The probing LED directs an incident light beam onto the surface of the deposition plate and the reflected light is measured by a light-sensing detector at the same wavelength. The ratio of reflected light to incident light provides an estimate of the incombustible fraction of material deposited relative to calibration points. A reference beam allows for automatic compensation due to deposition of particles on the emitter or detector cover plates. Because the surface coatings are expected to be thick in underground mines, the collection surface will be periodically cleaned by a high-amplitude frequency pulse applied to “shake” a majority of the accumulated dust off the mass sensing and optical reflective surfaces.

The contractor delivered four functional prototype sensors for NIOSH testing and evaluation. The sensors as part of an integrated communications system were evaluated both in NIOSH’s Experimental Coal Mine and the Dust Longwall Gallery in Bruceton, PA. SACCD node communications system evaluation was positive, but redesign of the sensors to more accurately evaluate coal float dust deposition is needed. Future testing is planned in the Dust Longwall Gallery, and the results of this evaluation will determine the merit for future refinement and development of the sensor nodes.