Improving protection against respirable dust at an underground crusher booth

Abstract

The U.S. National Institute for Occupational Safety and Health completed a 15-month study at an underground limestone mine crusher booth that evaluated three research parameters: (1) the effectiveness of a filtration and pressurization system for improving the air quality inside the operator booth, (2) the relative effectiveness of η > 99 and η > 95 experimental prototype filters in the system, and (3) the performance of three different cab pressure monitoring devices. The protection factor was quantified monthly using particle counters in the respirable dust range of 0.3 to 1 μm particle size, and gravimetric dust samples were gathered at the beginning and end of the overall study. Under static (closed-door) conditions, the filtration unit offered a gravimetric calculated protection factor between 10 and 31, depending on the filter type and loading condition. The monthly particle counting analysis shows that the η > 95 filter offers a protection factor nearly five times that of the η > 99 filter, where n = 15 samples. The booth pressure monitors were tested and proved to be a valid indicator of system performance over time.

Dust control handbook for industrial minerals mining and processing. Second edition.

“…Since there was no filtration on the OEM's ventilation system, the dust generated and liberated by the dumping process was blown directly into the crusher booth when the ventilation system was on. Later, an aftermarket filtration and pressurization system was installed and significantly improved the respirable air quality by a factor of 18.7 times [Patts et al 2017].…”

Design, testing, and modeling of environmental enclosures for controlling worker exposure to airborne contaminants.

“…Figure 17 (left) shows digital pressure instrumentation that can be electronically data logged (top) or monitored via an analog gauge (bottom) that can be visually observed by the enclosure occupant. Continuous pressure monitoring of an environmental enclosure showed pressure decreases for filter dust loading and pressure increases from filter replacement and enclosure integrity repairs, thereby enhancing timely maintenance actions [Patts et al 2017]. Figure 17 (right) shows a hotwire measurement of intake airflow being taken through a straight, smooth section of pipe attached to the cab enclosure.…”

“…Figure 17 (right) shows a hotwire measurement of intake airflow being taken through a straight, smooth section of pipe attached to the cab enclosure. This measurement directly indicates when intake airflow decreases below a desired minimum and the filter needs to be replaced [Cecala et al 2016, Patts et al 2017.…”

“…Another installation used a wall-mounted HVAC system on a crusher booth (368 ft 3 of volume) with two filtered intake pressurizers and recirculation filter units integrated into the HVAC system . A third installation used a ductless heat pump to temper the inside of an underground limestone mine crusher booth (458 ft 3 of volume), with a separate standalone single-filter system for cleaning both the intake and recirculation air [Patts et al 2017]. All of these systems provided a significant improvement in PF performance (8 to 216) compared to the negligible protection offered to workers in the previously unfiltered enclosures using typical window air conditioner units.…”

“…The smallest crusher booth achieved 0.04 to 0.12 in wg positive pressure for an intake airflow range of 97 to 213 ft 3 , providing PFs of 35 to 127 . Continuous differential pressure monitoring of the third underground limestone crusher booth indicated that its pressure was increased from 0.02 in wg to 0.11 in wg because of the 1.8-times increase in filtered airflow due to switching from a more restrictive 99% efficient filter to a less restrictive 95% efficient filter, which also improved the booth PF by more than four times [Patts et al 2017]. The booth's pressure was further increased by 0.07 in wg by sealing a leaky exterior roof duct plenum [Patts et al 2017].…”