Instituting a filtration/pressurization system to reduce dust concentrations in a control room at a mineral processing plant

Abstract

The National Institute for Occupational Safety and Health has observed that many control rooms and operator compartments in the U.S. mining industry do not have filtration systems capable of maintaining low dust concentrations in these areas. In this study at a mineral processing plant, to reduce respirable dust concentrations in a control room that had no cleaning system for intake air, a filtration and pressurization system originally designed for enclosed cabs was modified and installed. This system was composed of two filtering units: one to filter outside air and one to filter and recirculate the air inside the control room. Eighty-seven percent of submicrometer particles were reduced by the system under static conditions. This means that greater than 87 percent of respirable dust particles should be reduced as the particle-size distribution of respirable dust particles is greater than that of submicrometer particles, and filtration systems usually are more efficient in capturing the larger particles. A positive pressure near 0.02 inches of water gauge was produced, which is an important component of an effective system and minimizes the entry of particles, such as dust, into the room. The intake airflow was around 118 cfm, greater than the airflow suggested by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) for acceptable indoor air quality. After one year, the loading of the filter caused the airflow to decrease to 80 cfm, which still produces acceptable indoor air quality. Due to the loading of the filters, the reduction efficiency for submicrometer particles under static conditions increased to 94 percent from 87 percent.

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

“…A minimum recommended intake airflow quantity per person inside a cab enclosure is between 15 and 25 ft 3 /min [ASAE 1997;ASABE 2013a;ASHRAE 2007;CEN 2009a]. Eighty to 118 ft 3 /min delivered into a larger control room (1,440 ft 3 of volume) typically had less than 1,100 ppm of CO2 concentrations, which was more than adequate for human respiration by multiple people inside the enclosure [Noll et al 2015].…”

“…However, these larger enclosures were more difficult to seal and pressurize than smaller cab enclosures on mobile equipment. Only 0.01 to 0.02 inches of water gauge (in wg) of positive pressure was achieved with 80 to 118 ft 3 of intake air blown into the largest control room, which provided PFs from 8 to 25 [Noll et al 2015]. 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 .…”

“…Finally, several larger control room/booth case studies were conducted to examine the PF effectiveness of three different types of filtration system installations on much larger enclosures than typical mobile equipment cabs. One installation used a ductless heat pump to cool and heat the inside control room (1,440 ft 3 of volume) at a mineral processing plant, with a separate standalone two-filter system for cleaning the intake and recirculated air [Noll et al 2015].…”

Improving protection against respirable dust at an underground crusher booth

“…The U.S. National Institute for Occupational Safety and Health (NIOSH) has been conducting applied research to improve the air quality inside the enclosed cabs of mobile equipment, resulting in the mathematical modeling of enclosed cab filtration systems (Organiscak and Cecala, 2008). The same principles that govern the performance of filtration systems on mobile equipment are applicable to stationary enclosures such as operator booths and control rooms (Noll, Cecala and Hummer, 2015). While stationary enclosures are similar to mobile cabs, the work area can be significantly larger.…”