The goal of the present research was to assess, under controlled laboratory conditions, the accuracy and precision of a prototype device (named 'P.ALP': Ph.D. Air-quality Low-cost Project) developed for PM(2.5) concentration level monitoring. Indeed, this study follows a complementary manuscript (previously published) focusing on the in-field evaluation of the device's performance. Four P.ALP prototypes were co-located with the reference instrument in a calm-air aerosol chamber at the NIOSH laboratories in Pittsburgh, PA (USA), used by the Center for Direct Reading and Sensor Technologies. The devices were tested for 10 monitoring days under several exposure conditions. To evaluate the performance of the prototypes, different approaches were employed. After the data from the devices were stored and prepared for analysis, to assess the accuracy (comparing the reference instrument with the prototypes) and the precision (comparing all the possible pairs of devices) of the P.ALPs, linear regression analysis was performed. Moreover, to find out the applicability field of this device, the US EPA's suggested criteria were adopted, and to assess error trends of the prototype in the process of data acquisition, Bland-Altman plots were built. The findings show that, by introducing ad hoc calibration factors, the P.ALP's performance needs to be further implemented, but the device can monitor the concentration trend variations with satisfying accuracy. Overall, the P.ALP can be involved in and adapted to a wide range of applications because of the inexpensive nature of the components, the small dimensions, and the high data storage capacity.

A worker’s personal exposure to respirable dust in occupational environments has traditionally been monitored using established methodologies which entail the collection of an 8-h representative sample that is sent away for laboratory analysis. While these methods are very accurate, they only provide information on the average exposure during a specific time period, generally a worker’s shift. The availability of relatively inexpensive aerosol sensors can allow researchers and practitioners to generate real-time data with unprecedented spatial and temporal granularity. Low-cost dust monitors (LCDM) were developed and marketed for air pollution monitoring and are mostly being used to help communities understand their local and even hyper-local air quality. Most of these integrated sensing packages cost less than $300 per unit, in contrast to wearable or area dust monitors specifically built for mining applications which have been around for decades but still average around $5000 each. At the National Institute for Occupational Safety and Health (NIOSH), we are leveraging the power of high-volume data collection from networks of LCDM to establish baseline respirable hazard levels and to monitor for changes on a seasonal basis as well as following any application of control technologies. We have seen the effective use and advantages of monitoring live data before, during, and after events like shift changes, operational changes, ventilation upgrades, adverse weather events, and machine maintenance. However, many factors have prevented a systematic adoption of LCDMs for exposure monitoring: concern for their analytical performance, the complexity of use, and lack of understanding of their value are some factors. This contribution outlines a 1-year case study at a mine in Wisconsin, USA, covering the installation, maintenance, data visualizations, and collaboration between NIOSH researchers and the industrial hygiene professionals at the mine. © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2024.

Mining operations, by their very nature, create a lot of dust, with varying percentages of silica content. Modern mining operators are well aware of the hazard created by respirable crystalline silica dust (RCS). Operators also need to recognize that silicosis is an irreversible occupational disease with terrible consequences including lung cancer, respiratory failure and tuberculosis. And there is no cure for silicosis - the only fix is to prevent the disease by limiting worker exposure. Based on the latest work-related lung disease surveillance report by the CDC, between 1990 and 1999, just over 20% of all total silica deaths occurred in the M/NM industry. And between 2000 and 2017, 12% of MSHA personal heath samples were greater than the MSHA PEL of 100 ug/m3 and 34% of those were greater than the OSHA PEL of 50 ug/m3. The benefit of real-time dust sensing lies in the ability to help the operator understand when certain exposures occurred. Pairing real-time sensing with Helmet-CAM technology, mine operators can also understand the specific tasks that led to those exposures. Further adding the use of an FTIR instrument and end-of-shift analysis can effectively yield silica estimation. All three of these approaches can be combined to estimate real-time silica concentrations. Importantly, to quantify worker exposure, there is no substitute for personal sampling. Complementary to personal sampling is area sampling, and when area sampling is conducted in real time then the dust levels present at mines in key areas can be quantified on a continuous, long-term basis. NIOSH has conducted many years of engineering control research and has published extensively on the topic. While the commonly used hierarchy of controls puts substitution as the best method for reducing worker exposures, often in mining the best controls are engineering-based, such as exhaust ventilation, dust capture systems, and total structure ventilation. Fueled by a growing global desire to understand indoor and outdoor air quality (most commonly combustion aerosols in the atmosphere), numerous "low-cost" particulate sensors have been developed and marketed to those interested in quantifying their local air quality. Further, studies have compared these sensors to research-grade federal environmental monitoring devices and, after some appropriate scaling factor is applied, the agreement can be quite good. NIOSH recently began a new research effort in the fall of 2019 which aims to evaluate the applicability of these sensors not to ambient aerosols, but to the perhaps more challenging role of measuring real-time mining dust levels. This work poses many challenges - larger and more varied dusts, higher dust concentrations, and harsh environments - but the potential to inexpensively quantify mining dust levels in real time is intriguing. If low-cost area dust sensing for mining becomes a reality, it's possible that plant operators could apply engineering controls more widely by justifying installations that would most efficiently reduce both area exposures and individual worker exposures, providing a significant health benefit.

In May 1994, the National Institute for Occupational Safety and Health (NIOSH) considered crystalline silica to be a potential occupational carcinogen as defined by the Occupational Safety and Health Administration's (OSHA) carcinogen policy [29 CFR 1990], and this information was used in establishing the NIOSH Recommended Exposure Limit (REL) at 50 micro g/m3. NIOSH has long realized that occupational overexposure to respirable crystalline silica (RCS) dust can lead to the development of silicosis, an incurable and often fatal lung disease, but it can also result in health problems that include chronic obstructive pulmonary disease, tuberculosis, chronic bronchitis, emphysema and chronic renal disease. Probably the most significant occupational travesty that brought focus to the effects of silicosis was the Hawk's Nest Tunnel Disaster in southern West Virginia where a 4.83-km (3-mile) tunnel was driven through the Gauley Mountain. The material being removed during the mining of this tunnel for the development of a hydroelectric power plant was a sandstone and limestone ore containing very high levels of crystalline silica. Within months of the completion of this work, 476 of the workers died from acute silicosis. This acute silicosis was caused by extremely high respirable dust concentrations while driving this tunnel and was attributed to inconsistent dust-control methods, including poor ventilation and minimal use of water, not allowing the dust to settle after blasting occurred before workers returned back inside the tunnel and no use of respiratory protection.

The National Institute for Occupational Safety and Health (NIOSH) and the former U.S. Bureau of Mines (USBM) have given a significant effort over the past four decades in researching and developing engineering controls and interventions to reduce mine workers’ dust exposures during the bagging and palletizing of industrial minerals. Workers performing manual bagging and palletizing of 50- to 100-pound bags typically have some of the highest dust exposures of all workers at mining and mineral processing operations. This paper will provide an overview of available dust control technologies for bagging operations and present the findings of a recent case study that was conducted at four different industrial sand operations to identify the current types of bagging and palletizing technologies being used and to evaluate their effectiveness in reducing workers’ exposures to respirable crystalline silica dust. An evaluation will also be performed to determine if further reductions in respirable dust levels can be achieved by incorporating additional modifications or improvements into the existing technology.

Exposure to respirable crystalline silica (RCS) remains a serious health hazard to the US mining workforce who are potentially exposed as various ore bodies are drilled, blasted, hauled by truck, crushed, screened, and transported to their destinations. The current Mine Safety and Health Administration (MSHA) permissible exposure limit (PEL) for RCS remains at approximately 100 µg/m3, but it is noteworthy that the Occupational Safety and Health Administration (OSHA) has lowered its PEL to 50 µg/m3 (with enforcement dates staggered through 2022 for various sectors), and the National Institute for Occupational Safety and Health (NIOSH) has held a 50 µg/m3 recommended standard since 1976. To examine a method for reducing RCS exposure using a NIOSH-developed video exposure monitoring (VEM) technology (referred to as Helmet-CAM), video and respirable dust concentration data were collected on eighty miners across seven unique mining sites. The data was then collated and partitioned using a thresholding scheme to determine exposures that were in excess of ten times the mean exposure for that worker. Focusing on these short duration, high magnitude exposures can provide insight to implement controls and interventions that can dramatically lower the employee's overall average exposure. In 19 of the 80 cases analyzed, it was found that exposure could be significantly lowered by 20% or more by reducing exposures that occur during just 10 min of work per 8-hour shift. This approach provides a method to quickly analyze and determine which activities are creating the greatest health concerns. In most cases, once identified, focused control technologies or behavioral modifications can be applied to those tasks.

Video techniques for monitoring exposure, such as NIOSH’s “Helmet-CAM,” employ both real-time dust monitors and mobile video cameras to assess workers’ respirable dust exposures. Many real-time personally worn dust monitors utilize light scattering sensing elements, which are subject to measurement biases as a function of dust type (size, composition, shape factor) and environmental conditions such as relative humidity. These biased and inaccurate dust measurements impair the monitor’s ability to properly represent actual respirable dust concentrations. In the testing described, instrument mass concentration data was collected using three different types of commonly used commercial off-the-shelf personal dust monitors and compared to a reference standard. This testing was performed in a calm air (Marple) dust chamber in which three units of each make and model (for a total of nine monitors) were used for each test. Equivalency factors (EF, a multiplier to match the Thermo TEOM 1400a reference instrument) ranged between 0.746 and 1.879 across all dusts and environmental conditions tested, and between 0.821 and 1.519 on the ISO test dust.

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 n > 99 and n > 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 urn 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 n > 95 filter offers a protection factor nearly five times that of the n > 99 filter, where n = 15 samples. The booth pressure monitors were tested and proved to be a valid indicator of system performance over time. © Society for Mining Metallurgy and Exploration. All rights reserved.

After industrial sand has been mined and processed, the finished product is typically loaded into small bags of 45 kg (100 lb) or less, large bulk bags of 454 to 1,361 kg (1,000 to 3,000 lb), or vehicles such as trucks or trains for transport to end users. As the sand is being transferred and loaded, dust can be released into the work environment, potentially exposing workers to respirable crystalline silica. A number of control technologies have been developed and utilized in an effort to reduce dust liberation during loading operations. For bulk loading into trucks or trains, the U.S. National Institute for Occupational Safety and Health (NIOSH) evaluated one of these technologies, the Dust Suppression Hopper (DSH), at two industrial sand processing plants. Results from these case studies show that the DSH reduced airborne respirable dust levels by 39 to 88 percent, depending upon the product size being loaded.

Coal dust produced during underground coalmining, i.e. float dust, which deposits throughout the coal mine can be feedstock for coal dust explosions. To prevent these explosions, inert rock dust (limestone dust) is applied to roof, floor, and ribs areas of a coal mine. The ratio of incombustible mass (rock dust + incombustible content of coal dust) divided by total mass of the deposited dust is defined as the Total Incombustible Content (TIC) of the deposited dust within the mine. Regulations require that a minimum TIC ratio (80%;) to be maintained for safe working conditions inside the mine. This paper presents design, fabrication and experimental results for a real-time sensing module which uses continuous optical and dielectrometry methods to measure the TIC of the deposited float dust/rock dust. The optical sensor determines the TIC of the deposited dust based on optical reflection which is described by modified Beer Law. We present an extension of the Bouguer-Beer-Lambert Law to find the relation between the reflectivity of a layer of known thickness (obtained by interdigital dielectrometry sensor) of a dust mixture to the ratio of each constituent. We also present the experimental results from testing the sensor prototypes in a realistic laboratory test bed that is subjected to the deposition of the coal dust/rock dust mixture. The sensor performance and stability at different humidity levels is evaluated and the accuracy of the results are compared to the currently established best practices for measuring TIC in underground coal mines.

Controlling float coal dust in underground coal mines before dispersal into the general airstream can reduce the risk of mine explosions while potentially achieving a more effective and efficient use of rock dust. A prototype flooded-bed scrubber was evaluated for float coal dust control in the return of a continuous miner section. The scrubber was installed inline between the face ventilation tubing and an exhausting auxiliary fan. Airborne and deposited dust mass measurements were collected over three days at set distances from the fan exhaust to assess changes in float coal dust levels in the return due to operation of the scrubber. Mass-based measurements were collected on a per-cut basis and normalized on the basis of per ton mined by the continuous miner. The results show that average float coal dust levels measured under baseline conditions were reduced by more than 90 percent when operating the scrubber.

Airborne coal dust generated during mining can deposit and accumulate on mine surfaces, presenting a dust explosion hazard. When assessing dust hazard mitigation strategies for airborne dust reduction, sampling is done in high-velocity ventilation air, which is used to purge the mining face and gallery tunnel. In this environment, the sampler inlet velocity should be matched to the air stream velocity (isokinetic sampling) to prevent oversampling of coarse dust at low sampler-to-air velocity ratios. Low velocity ratios are often encountered when using low flow rate, personal sampling pumps approved for use in underground mines. In this study, with a goal of employing mine-ready equipment, a personal sampler was adapted for area sampling of coarse coal dust in high-velocity ventilation air. This was done by adapting an isokinetic nozzle to the inlet of an Institute of Occupational Medicine (Edinburgh, Scotland) sampling cassette (IOM). Collected dust masses were compared for the modified IOM isokinetic sampler (IOM-MOD), the IOM without the isokinetic nozzle, and a conventional dust sampling cassette without the cyclone on the inlet. All samplers were operated at a flow rate typical of personal sampling pumps, 2 L/min. To ensure differences between collected masses could be attributed to sampler design and were not influenced by artifacts from dust concentration gradients, relatively uniform and repeatable dust concentrations were demonstrated in the sampling zone of the National Institute for Occupational Safety and Health experimental mine gallery. Consistent with isokinetic theory, greater differences between isokinetic and non-isokinetic sampled masses were found for larger dust volume-size distributions and higher ventilation air velocities. Since isokinetic sampling is conventionally used to determine total dust concentration, and isokinetic sampling made a difference in collected masses, the results suggest when sampling for coarse coal dust the IOM-MOD may improve airborne coarse dust assessments over "off-the-shelf" sampling cassettes.

Airborne coal dust mass measurements in underground bituminous coal mines can be challenged by the presence of airborne limestone dust, which is an incombustible dust applied to prevent the propagation of dust explosions. To accurately measure the coal portion of this mixed airborne dust, the National Institute for Occupational Safety and Health (NIOSH) developed a sampling and analysis protocol that used a stainless steel cassette adapted with an isokinetic inlet and the low temperature ashing (LTA) analytical method. The Mine Safety and Health Administration (MSHA) routinely utilizes this LTA method to quantify the incombustible content of bulk dust samples collected from the roof, floor, and ribs of mining entries. The use of the stainless steel cassette with isokinetic inlet allowed NIOSH to adopt the LTA method for the analysis of airborne dust samples. Mixtures of known coal and limestone dust masses were prepared in the laboratory, loaded into the stainless steel cassettes, and analyzed to assess the accuracy of this method. Coal dust mass measurements differed from predicted values by an average of 0.5%, 0.2%, and 0.1% for samples containing 20%, 91%, and 95% limestone dust, respectively. The ability of this method to accurately quantify the laboratory samples confirmed the validity of this method and allowed NIOSH to successfully measure the coal fraction of airborne dust samples collected in an underground coal mine.

A series of laboratory tests were conducted to assess the effects of Fe-containing fuel additives on aerosols emitted by a diesel engine retrofitted with a sintered metal filter (SMF) system. Emission measurements performed upstream and downstream of the SMF system were compared, for cases when the engine was fueled with neat ultralow sulfur diesel (ULSD) and with ULSD treated with two formulations of additives containing Fe-based catalysts. The effects were assessed for four steady-state engine operating conditions and one transient cycle. The results showed that the SMF system reduced the average total number and surface area concentrations of aerosols by more than 100-fold. The total mass and elemental carbon results confirmed that the SMF system was indeed very effective in the removal of diesel aerosols. When added at the recommended concentrations (30 p.p.m. of iron), the tested additives had minor adverse impacts on the number, surface area, and mass concentrations of filter-out (FOut) aerosols. For one of the test cases, the additives may have contributed to measurable concentrations of engine-out (EOut) nucleation mode aerosols. The additives had only a minor impact on the concentration and size distribution of volatile and semi-volatile FOut aerosols. Metal analysis showed that the introduction of Fe with the additives substantially increased Fe concentration in the EOut, but the SMF system was effective in removal of Fe-containing aerosols. The FOut Fe concentrations for all three tested fuels were found to be much lower than the corresponding EOut Fe concentrations for the case of untreated ULSD fuel. The results support recommendations that these additives should not be used in diesel engines unless they are equipped with exhaust filtration systems. Since the tested SMF system was found to be very efficient in removing Fe introduced by the additives, the use of these additives should not result in a measurable increase in emissions of de novo generated Fe-containing aerosols. The findings from this study should promote a better understanding of the benefits and challenges of using sintered metal systems and fuel additives to control the exposure of underground miners and other workers to diesel aerosols and gases.

The contribution of heavy-duty haulage trucks to the concentrations of aerosols and criteria gases in underground mine air and the physical properties of those aerosols were assessed for three fuel blends made with fatty acid methyl esters biodiesel and petroleum-based ultra-low-sulfur diesel (ULSD). The contributions of blends with 20, 50, and 57% of biodiesel as well as neat ULSD were assessed using a 30-ton truck operated over a simulated production cycle in an isolated zone of an operating underground metal mine. When fueled with the B20 (blend of biodiesel with ULSD with 20% of biodiesel content), B50 (blend of biodiesel with ULSD with 50% of biodiesel content), and B57 (blend of biodiesel with ULSD with 57% of biodiesel content) blends in place of ULSD, the truck's contribution to mass concentrations of elemental and total carbon was reduced by 20, 50, and 61%, respectively. Size distribution measurements showed that the aerosols produced by the engine fueled with these blends were characterized by smaller median electrical mobility diameter and lower peak concentrations than the aerosols produced by the same engine fueled with ULSD. The use of the blends resulted in number concentrations of aerosols that were 13-29% lower than those when ULSD was used. Depending on the content of biodiesel in the blends, the average reductions in the surface area concentrations of aerosol which could be deposited in the alveolar region of the lung (as measured by a nanoparticle surface area monitor) ranged between 6 and 37%. The use of blends also resulted in slight but measurable reductions in CO emissions, as well as an increase in NOX emissions. All of the above changes in concentrations and physical properties were found to be correlated with the proportion of biodiesel in the blends.

A comparative human performance evaluation of a miner's walking speed and head pitch was conducted on miners wearing two types of LED cap lamps. Walking speed and head pitch are indirect indicators of improved lighting. The better that miners can see the floor, the faster they can walk and the less they pitch their heads downward to illuminate the floor with their cap lamps. NIOSH researchers developed a non-contact way to quantify human performance by using two small wireless, wearable inertial measurement units. Data were collected in the field from nine coal miners in an underground coal mine. The field results showed no statistical difference between the two cap lamps for walking speed. However, there was a trend of 2\circ lower head pitch for one of the cap lamps. The field testing procedures were then replicated in a controlled laboratory environment and the results indicated a 5-degree lower head tilt when using the same cap lamp and a corresponding difference in walking speed. A novel application of magnetometers for distance flagging is also presented. Finally, study limitations and a follow-up study are discussed.

Using biodiesel in place of petroleum diesel is considered by several underground metal and nonmetal mine operators to be a viable strategy for reducing the exposure of miners to diesel particulate matter. This study was conducted in an underground experimental mine to evaluate the effects of soy methyl ester biodiesel on the concentrations and size distributions of diesel aerosols and nitric oxides in mine air. The objective was to compare the effects of neat and blended biodiesel fuels with those of ultralow sulfur petroleum diesel. The evaluation was performed using a mechanically controlled, naturally aspirated diesel engine equipped with a muffler and a diesel oxidation catalyst. The effects of biodiesel fuels on size distributions and number and total aerosol mass concentrations were found to be strongly dependent on engine operating conditions. When fueled with biodiesel fuels, the engine contributed less to elemental carbon concentrations for all engine operating modes and exhaust configurations. The substantial increases in number concentrations and fraction of organic carbon (OC) in total carbon over the baseline were observed when the engine was fueled with biodiesel fuels and operated at light-load operating conditions. Size distributions for all test conditions were found to be single modal and strongly affected by engine operating conditions, fuel type, and exhaust configuration. The peak and total number concentrations as well as median diameter decreased with an increase in the fraction of biodiesel in the fuels, particularly for high-load operating conditions. The effects of the diesel oxidation catalyst, commonly deployed to counteract the potential increase in OC emissions due to use of biodiesel, were found to vary depending upon fuel formulation and engine operating conditions. The catalyst was relatively effective in reducing aerosol number and mass concentrations, particularly at light-load conditions, but also showed the potential for an increase in nitrogen dioxide concentrations at high-load modes.

Three types of uncatalyzed diesel particulate filter (DPF) systems, three types of high-temperature disposable filter elements (DFEs), and one diesel oxidation catalytic converter (DOC) were evaluated in underground mine conditions for their effects on the concentrations and size distributions of diesel aerosols. Those effects were compared with the effects of a standard muffler. The experimental work was conducted directly in an underground environment using a unique diesel laboratory developed in an underground experimental mine. The DPF systems reduced total mass of aerosols in the mine air approximately 10-fold for light-load and 20-fold or more for high-load test conditions. The DFEs offered similar reductions in aerosol mass concentrations. The efficiency of the new DFEs significantly increased with accumulation of operating time and buildup of diesel particulate matter in the porous structure of the filter elements. A single laundering process did not exhibit substantial effects on performance of the filter element. The effectiveness of DPFs and DFEs in removing aerosols by number was strongly influenced by engine operating mode. The concentrations of nucleation mode aerosols in the mine air were found to be substantially higher for both DPFs and DFEs when the engine was operated at high-load modes than at low-load modes. The effects of the DOC on mass and number concentrations of aerosols in mine air were relatively minor when compared to those of the DPF and DFE systems. copyright 2009 American Chemical Society.