Page 224 - Advanced Mine Ventilation

204 Advanced Mine Ventilation

12.5.3.1 Sources of Quartz

The sources of quartz in each mine were identified by collecting channel samples of the
roof, floor, and coal seam. These samples were analyzed by Materials Consultants and
Laboratories Inc. (MCL), a subsidiary of Carnegie Mellon University, by the X-ray
diffraction method. Quartz percentages are summarized in Table 12.5.
As can be seen, little quartz exists in the coal seam itself. The major sources of
quartz are the roof and floor. Thus, excessive quartz percentages found in respirable
dust samples are most probably due to mining practices, such as mining the roof or
floor to provide adequate working height or to eliminate bad top or mining of coal
seams with siliceous rock bands. The practices are often unavoidable and sometimes
even necessary for the safety of workers.

12.5.3.2 Comparison of X-ray Diffraction and Infrared
Techniques
A limited effort was made to compare the IR analytical technique with the X-ray tech-
nique. Mining sections in different mines put on reduced dust standards by MSHA
were resampled immediately after MSHA sampling at the operator’s canopy of the
continuous miner. These samples were sent to MCL for quartz analyses by X-ray
diffraction. Results of these analyses along with corresponding MSHA analyses are
listed in Tables 12.6 and 12.7.
The samples were not collected on the same day as were MSHA’s but were in the
same section during the time the reduced standard was in effect. In all cases, the per-
centage quartz determined by MCL was lower than MSHA’s. This difference could be
due to two factors. First, MCL used X-ray diffraction and MSHA used the IR method;
and as was shown previously, a large systematic difference could exist between the
two methods. But, it is not likely that the difference could be as great as is shown

Table 12.5 Quartz Percentages in Coal Mines
Sample Range of Quartz Percentage Average Percent Quartz
Roof (16) 4.0e21.0 12.0
Floor (16) 3.2e32.0 12.9
Coal seam (20) 0.0e4.3 2.0
Rock dust (16) 0.0 0.0

( ) Number of samples.