Page 126 - Advances In Productive, Safe, and Responsible Coal Mining

110 Advances in Productive, Safe, and Responsible Coal Mining

sensor technology to determine human posture [12–14]; however, these studies were
ultimately concerned with human position in specific postures. NIOSH research iden-
tified underground worker postures and determined the transition between them. This
research shows that by measuring and acquiring key reference joint angles, under-
ground mine worker posture can be analyzed and determined.
Determining worker posture can be important because the height of the MWC can
change dramatically with changes in posture. As described earlier, EM fields are a
revolving shell about the generator axis. Fig. 7.5 depicts a hypothetical way that a dif-
ference in posture could cause a change in detection distance. In the case depicted, the
shape is such that a kneeling miner could get closer to the machine than a standing
miner.
In underground field tests, the stop zone distance with the MWC at a height of 16in.
(40.6cm) was typically within 18in. (46cm) of the stop distance with the MWC at a
height of 46in. (116.8cm). In some cases, however, a difference of between two and
3 ft (0.6–0.9m) was observed. Similar observations were made relative to the warning
zone. The 46- and 16-in. heights correspond to the 95th percentile waist height for an
adult male in a standing position and the 5th percentile waist height for an adult female
in a kneeling position, respectively.

7.4.4 Current magnetic system performance
NIOSH researchers conducted field tests on magnetic-field-based PDS installed on
CMMs in active underground coal mines with seam heights ranging from 54 to 84in.
(137.2–213.4cm). Nine field tests were conducted throughout the United States to

Fig. 7.5 Effect of posture on detection distance.