Which Of These Filters Is Associated With Airflow

Min Eng. Author manuscript; available in PMC 2016 Aug 12.

Published in terminal edited form as:

Min Eng. 2016 Aug; 68(8): fifty–58.

PMCID: PMC4982552

NIHMSID: NIHMS807474

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

Abstruse

Pregnant 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 expanse, i 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 exist that they would as well 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 report, that filters with minimum efficiency reporting value, or MERV rating, of 16 may be a more appropriate selection than HEPA filters in most cases for the mining industry. A study was therefore performed comparison HEPA and MERV xvi filters on ii kinds of undercover limestone mining equipment, a roof bolter and a face drill, to evaluate this theory. Testing showed that, at the 95-per centum confidence level, in that location was no statistical difference between the efficiencies of the two types of filters on the two kinds of mining equipment. Every bit 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 exist 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.

Introduction

When most wellness and safety professionals think today near filtration efficiencies and their correlation with protecting workers' health, the normal supposition is the higher the efficiency of a filter, the greater the protection afforded to the workers. The next logical footstep is to believe that filters coming together the loftier-efficiency particulate arrestance (HEPA) standard evangelize the greatest protection for workers considering they provide the highest filtering efficiency. Obviously, high-efficiency intake filters are a necessity for an effective cab filtration and pressurization system on mobile mining equipment, merely what is the optimal filter efficiency for achieving high levels of cab protection factor (PF) functioning over the service life of filters? To address this question, an in-depth U.S. National Institute for Occupational Safety and Health (NIOSH) laboratory research study was performed over several years with numerous simultaneous field studies to retrofit enclosed cabs in use on mobile mining equipment with newer and more effective filtration and pressurization systems.

Table 1 summarizes the minimum efficiency reporting values, commonly known equally MERV ratings, and filtration efficiencies corresponding to iii size ranges of dust/contaminant particles, obtained from the American Society of Heating, Refrigerating and Air-Conditioning Engineers Handbook (ASHRAE, 2012), with the HEPA efficiency added at the bottom for comparison. A MERV rating is a value designated past ASHRAE to compare the effectiveness of different air filters, while HEPA is the about common filtration term known today, recognized by nearly nonhealth and rubber professionals.

Tabular array 1

MERV ratings and filtration efficiencies for three size ranges of dust particles (ASHRAE, 2012), and HEPA efficiency.

		Boilerplate particle size efficiency (PSE)

Group	MERV rating	0.3–1.0 µm	1.0–3.0 µm	3.0–ten.0 µm

	1			<20%
1	two			<twenty%
	3			<xx%
	4			<xx%

	5			20–34.nine%
two	6			35–49.ix%
	7			50–69.9%
	8			70–84.9%

	9		<50%	≥85%
three	ten		50–64.ix%	≥85%
	11		65–79.nine%	≥85%
	12		80–89.9%	≥90%

	13	<75%	≥90%	≥xc%
four	xiv	75–84.nine%	≥ninety%	≥90%
	15	85–94.ix%	≥90%	≥90%
	xvi	≥95%	≥95%	≥95%
HEPA		≥99.97%	≥99.97%	≥99.97%

To be rated as HEPA quality, filters must meet specifications set by the U.S. Department of Free energy and must be capable of filtering at least 99.97 percent of particles sized 0.3 µm and larger, and Table 1 shows a considerable jump in filtration efficiency for 0.3-µm particles and larger from ≥95 percent for MERV 16 filters to ≥99.97 percent for HEPA filters. Along with their wide recognition comes the assumption that HEPA filters should be used in nigh all applications. Still, these filters are more costly and restrictive than MERV xvi filters, placing additional demands on the overall filtering system, including the intake fan. The increased restriction and pressure drop across HEPA filters event in decreased intake airflow and lower positive pressure within the cab, both of which are detrimental to the overall system performance. This situation also raises the likelihood of leakage effectually the filter if the design and construction of the filter housing has modest imperfections.

When dealing with mobile equipment used in the mining and construction industries, because of the constant motility, vibration and stress placed on the enclosed cab over years of use, the likelihood of stress cracks and leakage points in the heating, ventilating and air conditioning (HVAC) and filtration arrangement becomes more of an issue. Based upon the results of a previous NIOSH laboratory report analyzing diesel particulate matter, we hypothesized that a MERV 16 intake filter using a mechanical filter media would exist the optimal design for the majority of enclosed cabs for mining applications, rather than a HEPA filter (Cecala et al., 2016; Cecala et al., 2014; Noll, Cecala and Organiscak, 2011, 2014).

When the research to improve air quality in the enclosed cabs of mobile equipment was started nigh 15 years ago, NIOSH's Pittsburgh Mining Enquiry Partitioning conducted the assay by performing gravimetric sampling and using lite-handful nephelometers to obtain instantaneous measurements inside and outside of the enclosed cabs during in-mine testing. This sampling procedure was time consuming, besides equally complicated, considering it included the time periods when the equipment operator was entering and exiting the cab, which allowed dust and contaminants to enter (Cecala et al., 2007; Heitbrink et al., 2000).

In contempo years, particle counters have advanced in many means, becoming more economical and unproblematic to use, and these instruments have improved the accuracy of the testing in this enquiry. The current report was performed using particle counters during nonproduction time periods while the roof bolter and face drill were located outside the mine. We believe these static conditions provide much more than reliable results and the most favorable and comparable PF values for each enclosed cab. Nosotros besides believe that this study is the starting time of its kind, attempting to compare HEPA and MERV 16 filters in the same enclosed cabs of mining machinery used in the manufacture.

Testing

A comparative evaluation was performed of the air quality in the enclosed cabs of a roof bolter and a face drill (J.H. Fletcher & Co., Huntington, WV) using MERV sixteen and HEPA filters. Identical examination protocols were implemented for each test series to attain, equally close as is practical, identical tests over the study menstruum. Figure i shows the filtration and pressurization unit on the face drill along with a program view of the system blueprint, which was identical on the roof bolter. Each filtration and pressurization unit used a RESPA-CF Vortex HyperFLOW intake air filtration pressurizer unit of measurement (Sy-Klone International, Jacksonville, FL) and a concluding panel filter (J.H. Fletcher & Co., Huntington, WV) within the HVAC component, through which all the intake and recirculation air flowed before entering the cab. The intake air filter pressurizer contained a cyclonic precleaner that used a centrifugal design to expel dust particles sized greater than 5.0 µm and prevent them from depositing on the filter, thus minimizing dust loading and extending filter life. Standardsize RESPA-CF filter cartridges, fifteen.24 cm (6 in.) in diameter and 20.32 cm (eight in.) high, were used throughout the study. The J.H. Fletcher & Co. concluding panel filter, with width of 28.91 cm (11.38 in.), superlative of 44.45 cm (17.5 in.) and thickness of 9.53 cm (3.75 in.), was mounted at the exhaust belch of the HVAC organization. All cab testing was conducted with the pressurizer unit of measurement operating and the HVAC system fan on the high flowrate setting. A matrix evaluation of several filter system configurations was too performed as a secondary study component, as well as a comparison of new versus used filters.

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Actual filtration and pressurization unit on an enclosed cab (left) with corresponding plan-view design drawing and airflow pattern (right).

The study was conducted at the new Shelly Materials underground limestone mine almost Zanesville, OH. At the end of the daylight shift, the equipment operators would bring their equipment outside the mine to service. When servicing was completed, the operators would park the roof bolter or face drill outside the mine and turn it over to us to perform our testing. At no time in the study did the operators and mine personnel clean or replace any filters associated with this testing. The ii most important measurements of the NIOSH test protocol were particle count, to determine a PF value for the filtration and pressurization organization's effectiveness for each of the enclosed cabs, and airflow, to determine intake and recirculation air volumes during each exam that were compared over time every bit the filters loaded with dust. Engine hours were also recorded each month during testing to provide a relative measure of equipment use and dust loading on the filters over time. At the offset of the testing, we installed a force per unit area monitoring device and datalogger in the enclosed cab of the confront drill and that of the roof bolter to determine and record the positive cab pressure level created by the filtration and pressurization system, aimed at documenting how the positive pressure decreased over fourth dimension as the filters loaded with dust and created additional filter differential pressure level, which would cause the airflow to decrease. The datalogger was attached to the pressure monitor and could record one-minute pressure averages for 28 days. We returned within the 28 days to download the positive pressure level information and conduct particle count and airflow measurements.

Testing was performed in a static mode, meaning the equipment was running without anyone in the enclosed cab to stir up or create any in-cab dust sources. This provided the highest possible PF for each of the enclosed cabs. From May through November of 2013, roughly on a monthly footing, testing was performed using MERV xvi intake and final filters. The testing was then repeated from May through November of 2014 using HEPA intake and final filters.

Particle count measurements

Two ARTI/Met One HHPC-6 particle counters (Hach Ultra Analytics, Grants Pass, OR) were used to simultaneously sample and record the inside and exterior cab particle size concentrations for one-infinitesimal periods over a 30-infinitesimal 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. The exam medium was airborne particles present in the ambient air surrounding the unoccupied stationary cab enclosure with the filtration system operating on the loftier fan setting. The inside and outside cab instruments were then alternated for another 30-minute test to boilerplate out any instrument sampling biases for each examination. The terminal 15 minutes of data from each test were used to calculate the boilerplate exterior and within cab concentrations during the lowest steady-state particle count conditions. The PFs were determined from the cumulative submicrometer (0.iii–1.0 µm) particle concentrations because about 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 boilerplate outside particle concentration by the average within particle concentration. The calculated PF for the cab was the boilerplate of these two test replicates. The 95 per centum conviction levels of the PFs were determined by calculating the propagation of standard error estimates (for a 2-variable ratio) during each test replicate and pooling these standard errors using Satterthwaite'southward standard error approximation (Organiscak, Cecala and Noll, 2013). Because of the comparative nature of this study, any effects from inapplicable factors from testing at a mine site are believed to exist minimal. The PF represents a reduction ratio of all the outside and interior particles removed by dividing the outside concentration past the inside concentration and is the same calculation used when determining the effectiveness of personal protective equipment such equally respirators.

Airflow and cab pressure measurements

Airflow readings were taken for the intake and recirculation circuits of the cab enclosures' filtration system for diverse filter combinations. During the field study, a VelociCALC 8346 hotwire anemometer (TSI Inc., Shoreview, MN) was used to measure the centerline air velocity in the eye of a 76.2-cm (30-in.)-long section of a smoothen PVC pipe with diameter of 6.ten cm (2.4 in.) that was added to the outlet of the intake filtering unit. For the recirculation component, one-minute moving traverse velocity measurements were taken with a vane anemometer (Davis Instruments, Vernon Hills, IL) over the recirculation filter inlet area. A more detailed description of these measurements can exist establish in Cecala, Organiscak and Noll (2012).

The cabs' inside-to-outside differential static pressures were besides measured to ensure that cab pressurization was achieved. During the MERV xvi filter testing in 2013, the KT-CABPRES-EL1-ENG electronic force per unit area monitor organisation 0.0–200 Pa (0.8-in. water guess) (Sy-Klone International, Jacksonville, FL) was used. During the HEPA filter testing in 2014, the DM-2003-LCD differential pressure transmitter 0.0–125 Pa (0.500-in. water gauge) (Dwyer Instruments, Inc., Michigan City, IN) was used. Both of these static force per unit area monitors had electronic outputs. The pressure level data were downloaded to a HOBO U12-006 datalogger (Onset Computer Corp., Pocasset, MA) and stored on the datalogger as one-minute pressure averages for upward to a 28-day catamenia.

Results

Effigy 2 shows the PFs determined for the enclosed cabs of the face drill and roof bolter, besides every bit the intake airflows with the MERV sixteen filters and the HEPA filters. The PF values, plotted on a log-normal scale, show significant improvements in air quality achieved with both types of filters for both the confront drill and the roof bolter. There are three missing data points: the kickoff two for the face drill and the roof bolter in October 2013 due to a several-calendar week federal government shutdown that started on Oct. 1, and the 3rd for the test on Aug. 27, 2014, in which the face drill was non operational.

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PFs determined from particle countings of the enclosed cabs of the face drill and the roof bolter, and comparison of the intake airflows with the MERV 16 filters and the HEPA filters.

The PFs for the face drill ranged from 612 to 6,337 for the MERV 16 filters and 685 to 8,133 for the HEPA filters. This compares with PFs for the roof bolter of 77 to one,021 for the MERV 16 filters and 182 to 1,425 for the HEPA filters. Based upon these ranges, the supposition would be that the HEPA filters provided college PFs than the MERV sixteen filters, just when all the values were averaged over the unabridged test period, this was not the case, equally shown in Fig. 3. For the face drill, the average PF was three,898 with the MERV 16 filters, slightly higher than the average PF of iii,677 with the HEPA filters. For the roof bolter, the average PF was 573 with the MERV xvi filters, slightly lower than the average PF of 681 with the HEPA filters. Statistically, at the 95 percent confidence level, there is no deviation between the PF values for either the confront drill or the roof bolter betwixt the 2 types of filters. This conclusion is based on insignificant differences found between the filter types when using a two-tailed parametric t-exam, assuming unequal variances, and a nonparametric Wilcox test. The 95 percent confidence levels for the cab PFs are also shown in Fig. 3 and illustrate no meaning differences between the filters used on each cab. There is, however, a significant difference in the PF values when comparing the enclosed cabs on the face drill with the roof bolter, which will be discussed in the post-obit section.

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Comparing of the boilerplate PF values for the face drill and roof bolter with the MERV 16 filters and the HEPA filters.

The offset point to note in the results is the extremely loftier Comparison of the boilerplate PF values for the face up drill and roof bolter with the MERV 16 filters and the HEPA filters. PF values for both the confront drill and the roof bolter, specially the face drill, indicating the tremendous improvement in air quality in the enclosed cabs. These PF values are the highest recorded in whatsoever of NIOSH'due south field testing to appointment, and it is believed that the static exam conditions and the use of a final filter were the two meaning contributing factors. In Organiscak, Cecala and Noll (2014), it was stated that any filtration and pressurization blueprint that directs all the intake and recirculation airflow through a final filter significantly increases the organisation'southward effectiveness, which was the case for the J.H. Fletcher blueprint in both the roof bolter and confront drill (Fig. ii).

Another interesting point to annotation is that for the MERV 16 filters, when the PF values for new filter conditions in May 2013 are compared with the values for the post-obit two readings in June and July, the results prove the intake and final filters loading with dust and becoming more than efficient. For the face drill, the PF was 612 with new filters, increasing to 4,106 for June and 6,337 for July. Similarly, for the roof bolter, the PF was 300 with new filters, increasing to 790 for June and 1,021 for July. Averaging the PF values for June and July, when the filters were loaded with grit, shows the substantial increase in filtering efficiency for both the face up drill and the roof bolter, with improvement factors of 8.5 and three.0 times the original, or clean filter, values, respectively.

This was not the case when considering the results of the HEPA filter testing, performed in 2014. At the start of the test, at that place were new intake and final filters in both the confront and the roof bolter. The intake filters loaded with dust as testing progressed, and one time the intake airflow dropped below the 0.71-m³/min level (25 cfm), a new intake filter was installed in the organization. For the HEPA testing, in that location were five instances when new intake filters were used: 3 for the face up drill and two for the roof bolter. In only 1 of these five instances was at that place a significant PF increment for the same 2-calendar month post-analysis used for the MERV 16 comparison. This occurred for the commencement HEPA filter test on the roof bolter, when there was a 3.two-times increase in the PF when the average of the 2 post-month values was compared with the PF value with all new filters. For the 3 instances of new intake filters on the face drill, at that place was i case of a very slight improvement of 1.1 times the original PF value.

The last point to highlight is the changes in intake airflow values shown in Fig. ii. In Cecala et al. (2014), it was stated that in club to provide a sufficient quantity of intake air to ensure the equipment operator does not get asphyxiated from being in an enclosed surface area, a minimum quantity of at least 0.71 mⁱⁱⁱ/min (25 cfm) is recommended to dilute the carbon dioxide exhaled by the operator (American Lodge of Agricultural and Biological Engineers, 2013). Based upon this value, it was determined during this study that whenever the intake airflow of either the face drill or the roof bolter reached or dropped below the 0.71-1000³/min (25-cfm) level, a new intake filter would exist installed. When this occurred, after taking the particle count and airflow measurements with the erstwhile filter, the new intake filter was installed, and the particle count and airflow measurements were repeated. For the testing of the MERV 16 filters, there were no intake filter changes necessary, although a new filter would have been needed on the face drill if the test had continued past November. For the HEPA filters, new intake filters were necessary on 2 occasions for the face drill on July 29 and Sept. 24, and on 1 occasion for the roof bolter on July 29. By comparing the declines in intake airflows for the MERV 16 filters with those for the HEPA filters on the face drill and on the roof bolter, it is seen how quickly the HEPA filters were loaded with dust and diesel particles, and needed to exist replaced. This is also apparent in Fig. 4, which plots the cab pressures and intake airflows for the face drill with the MERV 16 filters and with the HEPA filters. The effigy shows the starting points for the intake airflows and the cab pressures for both filter types, so how the values declined every bit both the intake and final filters loaded with dust. Figure 4 underscores the superior operating life cycle of the MERV 16 filters compared with the HEPA filters, with higher cab pressure throughout the life cycle, equally well as how an in-cab pressure level monitor tin can be used to betoken the need for filter changes. Recirculation airflows for both cabs were between 4.08 and seven.0 mⁱⁱⁱ/min (144 and 247 cfm) for the MERV 16 concluding filter and between 3.82 and 5.86 mⁱⁱⁱ/min (135 and 207 cfm) for the HEPA final filter with the HVAC on the highest fan setting during the study.

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Comparison of the intake airflows and positive cab pressures for the face drill with the MERV sixteen filters and the HEPA filters.

Discussion

Although this written report showed no long-term significant divergence in a cab's PFs when using the MERV sixteen filters and the HEPA filters, it did show a significant deviation between the roof bolter's and the face drill's PFs when using identical filters. This difference is speculated to be the event of sealing or integrity deviations betwixt the mechanical structures of the ii identical HVAC/filtration systems. Additional evidence to this effect was observed early on in the testing of the MERV 16 filters on the roof bolter, when particle count measurements were taken with several extra filter combinations, afterward 257 hours of operation, to examine the mathematical modeling of these system changes (Organiscak, Cecala and Noll, 2014). The filter combinations tested included adding a used recirculation filter to the system and removing the final filter from the system. Figure 5 shows the results of these tests as well as the examination when the intake and final MERV 16 filters were new. This figure also shows the modeled PFs adult in Organiscak, Cecala and Noll (2014) under these test configurations using their specified filter efficiencies, including intake, last, recirculation, new and used; measured airflows, for intake and recirculation; and an causeless intake air leakage of 2 per centum, or 0.02, with nada air current infiltration, which was assumed for positive cab pressurization. The recirculation filters used in the current study, whose 0.3–1.0 µm particle collection efficiencies were previously measured in the laboratory, significantly reduced the recirculation airflows of the HVAC organization (Organiscak, Cecala and Noll, 2014). These smaller recirculation filters, 7.62 cm (3 in.) high, forty.64 cm (16 in.) wide and v.08 cm (2 in.) thick, were placed in the recirculation filter location most the floor of the cabs for the additional testing (run into Fig. i).

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Roof-bolter cab performance changes with respect to different filters used in the system.

As illustrated in Fig. v, the measured PFs were notably lower than the modeled PFs. In society to achieve understanding between them, the intake air leakage into the system would accept to exist greater than 65 percent, or 0.65. This would appear to be an extreme corporeality of air leaking effectually the MERV sixteen intake air filter through small cracks or gaps in the HVAC organization, and it is more logical to surmise that in that location were probably boosted air leakages around the other filters in the organisation. Visual inspection of the HVAC arrangement with the filters removed on the roof bolter showed grit deposits downstream of the intake and last filters, indicating multiple leaks in the HVAC system effectually the filters. A more than refined cab filtration arrangement model was formulated by node analysis with these additional leaks (Cecala et al., 2016). This model is represented past the following equation:

$P F = \frac{C}{x} = \frac{Q_{I} + Q_{R} - [Q_{R} (1 - η_{R} + l_{R} η_{R}) (ane - η_{F} + 50_{F} η_{F})] + Q_{West}}{[Q_{I} (1 - η_{I} + 50_{I} η_{I}) (1 - η_{F} + 50_{F} η_{F})] + Q_{W}}$

where PF is the cab protection factor; C is the outside contaminant concentration penetrating the filtration organisation; x is the inside cab contaminant concentration; η is the filter reduction efficiency, fractional; one − η is the filter penetration, fractional; Q is the airflow quantity; l is the air leakage, fractional; and the subscripts F indicate final, I intake, R recirculation and West wind.

The equation provides for a more sensible proportioning of air leakages throughout the filtration organization. Face drill air leakages that were modeled bypassing the new intake, recirculation and final filters were 4, ii and 2 per centum, or 0.04, 0.02 and 0.02, respectively, which were doubled for modeling used filters at these locations. Roof bolter air leakages used in the model were farther doubled over those used for the face up drill, given its significantly lower cab PF field measurements. Boosted two- and three-filter system combinations – intake filter with final and/or recirculation filter; MERV sixteen and HEPA filters; new and used – were also tested on both of these cabs throughout this long-term study and were modeled using their measured airflow quantities and assumed proportional air leakages described to a higher place. For the two-filter systems, nix efficiency was used in the equation for the missing filter, thereby removing its air filtering effect from the model.

Figure half dozen shows a comparison of the measured cab PFs and the modeled cab PFs, with reasonable agreement along a unity line. The spread in the data is presumed to be primarily a result of the actual unknown field leakage deviations from the causeless modeled leakages. The effigy too shows that the lowest PFs were measured and modeled when no final filter was used. Additionally, the opening points in the figure evidence in that location was no observable cab PF benefit to adding the recirculation filter into this system when using the final filter. Adding the recirculation filter into the arrangement significantly reduced the recirculation airflow and cab PF, equally illustrated in Fig. 5. A negative aspect of not having the recirculation filter in the arrangement is that clay and dust from within the cab would go fatigued into and deposited in the HVAC system, thereby increasing maintenance bug. An alternative solution to improving this cab filtration arrangement would be to increase the size of the recirculation filter to increment its airflow capabilities. Finally, leakages in the HVAC/filtration organization accept a significant impact on cab PFs, as shown when comparing the measured and modeled PFs of the 2 vehicle cabs. Therefore, the cab HVAC/filtration system needs to be well-sealed to extract the benefits of using high-efficiency dust filters.

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Measured and modeled PFs of the face drill and the roof bolter during the filter field study.

Conclusion

A NIOSH comparative study was performed to evaluate the filtering efficiency and air quality inside the enclosed cabs of a roof bolter and a face drill being used at an underground limestone mine when using MERV 16 filters and HEPA filters. The confront drill and the roof bolter were each fitted with a filtration system composed of an intake filter and a last filter. The final filter provided a 2nd filtering of the intake air, along with filtering all the air recirculated from within the enclosed cab. The testing showed there was no statistical divergence betwixt these two filter types at the 95 percent confidence level for the face drill and the roof bolter. In near all cases when testing the HEPA filters, the PFs were at their highest when the filters were outset installed. Every bit testing progressed and these filters loaded with grit, the PFs, as well as the intake airflows, continually decreased until the system was not able to provide a sufficient intake airflow and the filters needed to be inverse.

In dissimilarity to the HEPA filters, the MERV 16 filters showed improved filtering efficiency over time and utilise as the filters loaded with dust. Considering the MERV 16 filters were less restrictive and provided greater cab pressure, they did not have to be replaced as often as the HEPA filters. This testing too showed the benefits of using a mechanical filtering media, which becomes more efficient with dust loading and the creation of a filter cake. For both the confront drill and the roof bolter used in this comparative study, the MERV 16 mechanical filter design was the optimal selection, not only for performance simply also for toll. As MERV sixteen filters are less expensive than HEPA filters and practice not need to be changed every bit oft, which significantly lowers maintenance labor costs, this equates to meaning cost savings.

Another central component of this testing was the validation of the substantial improvement in the effectiveness of filtration and pressurization systems when using a final filter blueprint. The final filter adds another level of filtration to remove particulates that leak around the other filters in the HVAC system. Still, filters used in the HVAC arrangement should be adequately sized so as not to restrict airflow, thus lowering the organisation's effectiveness. This was shown non only through the modification expansion of NIOSH'south model to include multiple filter applications but also from the actual test matrix performed on the filtration and pressurization systems of the face drill and the roof bolter.

Acknowledgments

We would like to admit Ted DiNardo, mine manager at Shelly Materials, located virtually Zanesville, OH, and the entire underground limestone mine crew, with special recognition to Jerry Siddle, mine foreman, Jay White, roof-bolter operator, and Harry Montell, face-drill operator. Additionally, we would like to acknowledge Sean Farrell, product engineer, and Ward Morrison, product manager, at Rock & Industrial Mineral Products, with J.H. Fletcher & Co., for their assistance and support of this research effort over a number of years. The cooperation and dedication of all these individuals were instrumental in the success of this study.

Footnotes

Disclaimer

Mention of any company or product does not constitute endorsement past NIOSH. The findings and conclusions in this report are those of the authors and practice non necessarily represent the views of NIOSH.

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