CDEM-1000 Coal Dust Explosibility Meter

Coal Dust Explosions Natural occurring methane in coal mines causes frequent explosions, which alone may not pose a major hazard. When a methane explosion prompts a coal dust explosion, the intensity is far greater. Coal dust explosions can cause deaths both directly and by trapping miners through mine cave-ins.

Rock Dusting in Coal Mines Coal dust explosions are averted in coal mines by applying layers of inert rock dust over the coal dust. The inert rock dust used in the US is commonly limestone, although marble dust may be used as well. MSHA may levy fines against coal companies that don’t maintain enough rock dust in their mines, based on a lab analysis.

CDEM-1000 The CDEM-1000 uses reflectivity of rock dust/coal dust mixtures to determine the % rock dust in the mixture. This works, because coal dust is black and the rock dust is white. The lighter color the mix, the more rock dust it contains. MSHA requires a rock dust/coal dust mix of at least 80% rock dust. The CDEM-1000 is a go/no-go meter that produces a green indication for % RD above 80.

CDEM-1000 The CDEM 1000 was developed by NIOSH at the Pittsburgh Research Laboratory. It is produced solely by Sensidyne, LP. It has an MSHA approval for intrinsic safety. It has been thoroughly field tested by both MSHA and NIOSH.

CDEM-1000 Kit The CDEM-1000 kit comes with all accessories required for field sampling.

Accessories A) CDEM-1000 B) PPC Samples C) Molecular sieves D) Calibration vials E) Calibration funnels F) Spatula and brush G) Sample vials H) Sample funnels I) Sample cups A G H I F E B C D

Collecting a Sample A sample of the mine’s coal dust/rock dust mixture is taken from the mine floor and walls according to an MSHA procedure. It is transferred to a sample vial.

Preparing a Sample The sample vial contains activated molecular sieves, small beads that absorb moisture. The beads are removed by a funnel with a small screen inside, as the sample is transferred to a sample cup.

Sample Size The dried sample is transferred to a sample cup, observing the cup’s fill line. The cup is placed against the CDEM- 1000’s lens. A spillover is expected.

Red/Green Indication The CDEM unit is a go-no- go meter. It is not an analytical tool. A green indication means that the rock dust is present in the sample mixture at 80% or more. A red indication means that more rock dust must be applied. An extended red function allows the user to see a range that represents how close the mix is to green (e.g. 75 to 78%).

Methane Consideration The CDEM will ask the user to input a methane value for the area. This value is read from a separate methane meter. The user can input methane values from 0.0 to 2.0% methane in 0.1% increments as read from the methane meter. For each 0.1% of methane, the CDEM-1000 will slide the green criteria upward by 0.4% rock dust. For example, a reading of 0.5% methane inputted into the CDEM-1000 will raise the green indication from 80% to 82% (i.e., 5 x 0.4% = 2%).

Calibration The unit is calibrated by exposing the lens in turn to 100% PPC. 100% RD and an 80% mixture of the mine’s rock dust and the PPC provided. The CDEM-1000 walks the user through the calibration steps through the LCD display. A calibration is required every field 200 samples.

Pittsburgh Pulverized Coal Calibration must be conducted using the PPC samples provided. They represent the coal dust particle size range that is most dangerous in mine explosions.

Rock Dust Rock dust used in the calibration procedure must come from the mine. The rock dust used by the mine must meet the correct size distribution specified by MSHA.

Reflectivity Check A reflectivity check is required after every 1000 field samples. The CDEM-1000 will prompt the user when the reflectivity check is due. To conduct this check, a special sample cup with a color standard permanently placed inside is exposed to the lens. This cup is matched to the CDEM-1000 unit by serial number. The unit will display a pass or fail based on its agreement with the standard’s % RD value, which is stored in the CDEM- 1000’s memory. The reflectivity sample cup doubles as a protective cup for shipping. It attaches to the unit bayonet style.

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