LABORATORY EVALUATION OF SHIELD DUST ENTRAINMENT IN HIGH VELOCITY AIRSTREAMS

摘要

In conjunction with steady increases in productionrnlevels, longwall operators have applied greaterrnquantities of ventilating air and spray water in anrneffort to control respirable dust and/or methane. Airrnvelocities greater than 7.6 m/s (1500 fpm) have beenrnmeasured on longwall faces. Operators havernexpressed concern over the potential entrainment ofrnrespirable dust at these high velocities. The greatestrnlikelihood for entraining dust into the high velocityrnairstream may occur as shields are advancedrnallowing relatively dry particles to fall from the shieldrncanopy directly into the airstream. Laboratory testsrnto simulate dust liberation during shield movementrnwere conducted at the Pittsburgh ResearchrnLaboratory of NIOSH at velocities ranging from 2.0rnto 8.2 m/s (400 to1600 fpm). Airborne dust samplesrnwere obtained with personal impactors to quantifyrnthe size distribution and concentration of the dustrnentrained at the various air velocities. Statisticallyrnsignificant increases in both total and respirable dustrnconcentrations were measured as test air velocitiesrnwere increased.