Field Assessment of Enclosed Cab Filtration System Performance Using Particle Counting Measurements

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.

Section: Resultsmentioning

confidence: 99%

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

Noll¹,

Cecala²,

Hummer³

2015

“…The booth’s protection factor for a particular test configuration was determined from the average of the two test replicates. The 95 percent confidence levels of these protection factors were determined by calculating the propagation of standard error estimate (for a two-variable ratio) during each test replicate and pooling these standard errors by using Satterthwaite’s standard error approximation as previously described by Organiscak, Cecala and Noll (2013).…”

Section: Particle Counting Methodsmentioning

confidence: 99%

Air cleaning performance of a new environmentally controlled primary crusher operator booth

Organiscak¹,

Cecala²,

Zimmer³

et al. 2016

The National Institute for Occupational Safety and Health (NIOSH) cooperated with 3M Company in the design and testing of a new environmentally controlled primary crusher operator booth at the company’s Wausau granite quarry near Wausau, WI. This quarry had an older crusher booth without a central heating, ventilation and air conditioning (HVAC) system, and without an air filtration and pressurization system. A new replacement operator booth was designed and installed by 3M based on design considerations from past NIOSH research on enclosed cab filtration systems. NIOSH conducted pre-testing of the old booth and post-testing of the new booth to assess the new filtration and pressurization system’s effectiveness in controlling airborne dusts and particulates. The booth’s dust and particulate control effectiveness is described by its protection factor, expressed as a ratio of the outside to inside concentrations measured during testing. Results indicate that the old booth provided negligible airborne respirable dust protection and low particulate protection from the outside environment. The newly installed booth provided average respirable dust protection factors from 2 to 25 over five shifts of dust sampling with occasional worker ingress and egress from the booth, allowing some unfiltered contaminants to enter the enclosure. Shorter-term particle count testing outside and inside the booth under near-steady-state conditions, with no workers entering or exiting the booth, resulted in protection factors from 35 to 127 on 0.3- to 1.0-μm respirable size particulates under various HVAC airflow operating conditions.

“…Two ARTI/Met One HHPC-6 particle counters (Hach Ultra Analytics, Grants Pass, OR) were used to simultaneously sample and record the inside and outside cab particle size concentrations for one-minute periods over a 30-minute test (NIOSH, 2008; Organiscak and Cecala, 2008; Organiscak, Cecala and Noll, 2013). These instruments count airborne particles in six size channels from 0.3 to greater than 5.0 µm.…”

Section: Particle Count Measurementsmentioning

confidence: 99%

“…The last 15 minutes of data from each test were used to calculate the average outside and inside cab concentrations during the lowest steady-state particle count conditions. The PFs were determined from the cumulative submicrometer (0.3–1.0 µm) particle concentrations because most of the ambient air particles resided in this size range (NIOSH, 2008; Organiscak, Cecala and Noll, 2013). A PF for each test replicate was determined by dividing the average outside particle concentration by the average inside particle concentration.…”

Section: Particle Count Measurementsmentioning

confidence: 99%

Comparison of MERV 16 and HEPA filters for cab filtration of underground mining equipment

Cecala¹,

Organiscak²,

Noll³

et al. 2016

Significant strides have been made in optimizing the design of filtration and pressurization systems used on the enclosed cabs of mobile mining equipment to reduce respirable dust and provide the best air quality to the equipment operators. Considering all of the advances made in this area, one aspect that still needed to be evaluated was a comparison of the efficiencies of the different filters used in these systems. As high-efficiency particulate arrestance (HEPA) filters provide the highest filtering efficiency, the general assumption would be that they would also provide the greatest level of protection to workers. Researchers for the U.S. National Institute for Occupational Safety and Health (NIOSH) speculated, based upon a previous laboratory study, that filters with minimum efficiency reporting value, or MERV rating, of 16 may be a more appropriate choice than HEPA filters in most cases for the mining industry. A study was therefore performed comparing HEPA and MERV 16 filters on two kinds of underground limestone mining equipment, a roof bolter and a face drill, to evaluate this theory. Testing showed that, at the 95-percent confidence level, there was no statistical difference between the efficiencies of the two types of filters on the two kinds of mining equipment. As the MERV 16 filters were less restrictive, provided greater airflow and cab pressurization, cost less and required less-frequent replacement than the HEPA filters, the MERV 16 filters were concluded to be the optimal choice for both the roof bolter and the face drill in this comparative-analysis case study. Another key finding of this study is the substantial improvement in the effectiveness of filtration and pressurization systems when using a final filter design.