Published in the March 2007 American Longwall Magazine

“The size of coal dust is relevant to the amount of rock dust required to inert the coal dust, with more rock dust needed to inert finer sizes of coal dust,” according to researchers from NIOSH and Mine Safety and Health Administration, who collaborated to determine coal dust sizes present in US operations. The collection is the first of its kind since the 1920s, when federal mining health and safety research resided under the US Bureau of Mines.

Once the coal dust sizes were determined, the baseline for the battery-powered meter was set and ready to put into use. Because rock dusting is a federal regulation for all underground coal mines, and regular checks are required, inspectors can most easily gauge dusting success by collecting samples.

To determine proper rock dusting, instead of taking a sample of an area and sending it offsite and waiting weeks to receive results, now the CDEM can provide miners and safety personnel with immediate readings.

Of course, the largest advantage to the rapid results is gathering instant feedback on the conditions in an area and its potential for an explosion. However, the device’s portability and ease of use makes it a potentially commonplace device used by workers and rock dusting personnel during the process.

Researchers Marcia Harris, Jürgen Brune and recently retired Mike Sapko have noted a potential increase in the efficiency of rock dusting practices. Because the need for dusting can be quantitatively assessed, an optimum balance between applied rock dust and existing explosive coal dust can be determined.

Not only can the dusting staff ensure a safe environment for those who will follow them in the section, they will also save time and fuel/battery life because the duster makes minimal passes over an area.

The entire process with the CDEM takes only a minute or so, said Harris. Once the test, which also measures and takes coal dust size into account, is completed, it will give a percentage readout and level of potential danger.

The regulations now require a minimum of 65% incombustible material in the intake entries and 80% or more in the return entries. The meter display screen will indicate red for a potentially hazardous dust mixture or green for a dust mixture that contains sufficient incombustible material so the dust mixture will not propagate an explosion.

The unit does require initial calibration to ensure accuracy. Sapko noted that a once-a-month calibration was sufficient. Users can carry small samples with them of pure rock dust, pure coal dust, and a known midpoint sample for checking the meter before each sampling survey.

Sapko, who originally developed the meter, also said that the application has been sent to the MSHA for certification of permissibility for use in underground coal mines. If all goes well, the team anticipates the unit could be released as early as summer this year. H&P Prototyping (mention of any company or product does not constitute endorsement by NIOSH) will produce and market the CDEM once it is approved and ready for sale.