Reducing Shuttle Car Operator Dust Exposure by Improving Continuous Miner Blowing Face Ventilation Parameters

Researchers at the National Institute for Occupational Safety and Health (NIOSH) performed laboratory testing to examine and improve airborne dust capture and methane removal performance of flooded-bed scrubbers on continuous mining machines using a blowing face ventilation configuration to reduce respirable dust exposure to shuttle car operators. Several testing conditions were examined to minimize shuttle car operator dust exposure without adversely affecting continuous miner performance and production. Curtain-to-face setback distance of 9.1 m versus 15.2 m (30 ft versus 50 ft), face ventilation airflow of 226.5 m3/min versus 339.8 m3/min (8,000 ft3/min versus 12,000 ft3/min), and the use of side-body-mounted blocking sprays (on versus off) were the three primary parameters compared. Scrubber airflow was set and maintained at 198.2 m3/min (7,000 ft3/min) throughout testing. An examination of slab cuts versus box cuts and the location of the shuttle car (present behind the continuous miner versus not present in the entry) was also performed to demonstrate the effects of these constantly changing scenarios on scrubber performance. Results show that the best blowing face ventilation setup for minimizing shuttle car operator dust exposure for the tested parameters uses a 15.2-m (50-ft) curtain-to-face setback with 339.8 m3/min (12,000 ft3/min) face ventilation while operating the side-body-mounted blocking sprays. INTRODUCTION Coal mine worker overexposure to respirable coal dust continues to be a problem in U.S. underground coal mining operations, potentially leading to coal workers’ pneumoconiosis (black lung). The U.S. Mine Safety and Health Administration (MSHA) requires that respirable dust exposure to coal mine workers does not exceed a 1.5 mg/m3 average over the actual working shift (79 Fed. Reg. 24814 (2014)). Although using a blowing face ventilation configuration on continuous miner (CM) sections is beneficial for removing methane emissions from the mining face, it can be detrimental for dust control for shuttle car (or ram car) operators and any other workers on the return ventilation side of the CM when compared to exhausting ventilation. Even with machine-mounted scrubbers on CMs, shuttle car operators still have some of the higher dust exposures with blowing face ventilation systems (NIOSH 2011, Beck et al. 2015). Although scrubber discharge air is not completely clean, dust being blown around the scrubber inlet and therefore not being captured by the scrubber can further increase these dust exposures (Goodman 2000). Dust control problems are also caused by inadequate face ventilation quantities causing scrubber face airflow recirculation issues (Schultz et al. 2010). In order to minimize respirable dust exposures on blowing face ventilation sections, ventilation, water spray, and scrubber parameters were experimentally examined to improve operating ranges for both dust and gas control. Several blowing face ventilation factors were examined with respect to CM spray systems and scrubber operation. Curtain-to-face setback distance and side-body-mounted blocking sprays were previously examined in the laboratory for dust control on a full-scale CM model using a scrubber on a blowing face ventilation system (Goodman 2000). The blocking sprays produced larger dust reductions at the CM’s rear corners and return for a 6.1-m (20-ft) curtain setback distance as compared to a 12.2-m (40-ft) curtain setback distance with equal face and scrubber airflows of 169.9 m3/min (6,000 ft3/min). Because face ventilation airflow quantities, shuttle car operator locations, and tracer gas concentration gradients were not previously examined during these experiments, additional research was required to determine improved operating parameters for blowing face ventilation systems.