Last data update: Jun 17, 2024. (Total: 47034 publications since 2009)
Records 1-13 (of 13 Records) |
Query Trace: Harris ML [original query] |
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Laboratory development and pilot-scale deployment of a two-part foamed rock dust
Brown CB , Perera IE , Harris ML , Chasko LL , Addis JD , Klima S . J Loss Prev Process Ind 2022 74 U.S. Code of Federal Regulations 30 CFR 75.402 and 75.403 require 80% total incombustible content to be maintained within 40 feet of the coal mine face via the liberal application of rock dust. Unfortunately, this application of rock dust limits miners' visibility downwind and can increase the miners' exposures to a respirable nuisance dust. Wet rock dust applied as a slurry is, at times, used to negate these negative effects. Although this aids in meeting the total incombustible limits, the slurry forms a hard cake when dried and no longer effectively disperses as needed to suppress a coal dust explosion. As a result, a dry rock dust must be reapplied to maintain a dispersible layer. Therefore, researchers from the National Institute for Occupational Safety and Health (NIOSH) have been working towards finding and testing a foamed rock dust formulation that can be applied wet on mine surfaces and remain dispersible once dried which minimizes the likelihood of mine disasters, including mine explosions. The initial tests were aimed at discerning dispersion characteristics of three different foamed rock dusts via the NIOSH-developed dispersion chamber and led to identification of a two-part foam with adequate dispersion characteristics. The current study was conducted to assess the robustness of the two-part foamed rock dust. Through a series of laboratory-scale experiments using the dispersibility chamber, the effects of testing conditions and product formulations on the foam's dispersibility was determined. Some of the tested variables include: exposing the foam to high humidity, varying the component levels of the foamed rock dust, altering the rock dust size distribution, and varying the rock dust types. Further pilot-scale tests examined the atmospheric concentrations of dust via personal dust monitors downwind of foamed rock dust production and application. Additionally, product consistency was recorded during pilot-scale testing at key points in the formulation and application. The results of these experiments will be discussed in this paper. © 2021 |
Analysis and Characterization of Anti-Caking Additives Used in Rock Dust to Mitigate Mine Explosions
Perera IE , Harris ML , Sapko MJ . Min Metall Explor 2021 38 (3) 1411-1419 Experiments conducted with limestone dusts and dolomitic marble dusts have indicated that when rock dust is wetted and subsequently dried, it becomes a solid, non-dispersible cake. However, in order to be effectively inert a coal dust explosion, rock dust must be able to disperse as individual particles to air. To counteract this, rock dust manufacturers created treated rock dusts that will resist caking after moisture exposure. National Institute for Occupational Safety and Health (NIOSH) researchers conducted a series of laboratory-scale experiments on four base rock dusts and their treated counterparts to assess the effectiveness of various anti-caking additives after being exposed to moisture and then dried. The dusts were exposed to moisture using humidity cabinets having a high relative humidity (99% RH) and by also exposing the rock dust bed to water through bottom wicking. The dusts were then evaluated for dispersibility after drying using the NIOSH-designed dust dispersion chamber. The anti-caking additives were different concentrations of stearic acid, oleic acid, and xylene-based surfactants. All results were compared to a reference rock dust used to conduct large-scale experiments in the Lake Lynn Experimental Mine (LLEM), Fairchance, PA. When the untreated dusts were dried after exposure to moisture for 1 day, no dispersion was measured. However, rock dusts treated with anti-caking agents were readily dispersible even after exposure to moisture for 6 months. This report details the analysis and characterization of anti-caking additives using the NIOSH-designed dispersion chamber and the 20-L explosion test chamber. © 2019, This is a U.S. government work and its text is not subject to copyright protection in the United States; however, its text may be subject to foreign copyright protection. |
Large-scale explosion propagation testing of treated and non-treated rock dust when overlain by a thin layer of coal dust
Perera IE , Harris ML , Sapko MJ , Dyduch Z , Cybulski K , Hildebrandt R , Goodman GVR . Min Metall Explor 2021 38 (2) 1009-1017 To prevent coal dust explosion propagations, rock dust needs to be lifted and suspended in the air with the coal dust during an explosion. The addition of anti-caking agents prevents caking of rock dust in the presence of water. Mining and rock dusting processes can frequently create alternating layers of rock dust and float coal dust on mine surfaces. For this test series, a thin layer of coal dust was distributed on top of a layer of either treated or non-treated rock dust in the Experimental Mine Barbara, Poland. The experimental results compare the effectiveness of treated and non-treated rock dusts to attenuate a propagating coal dust explosion initiated with either strong or weak methane explosions. Experimental results indicate that the treated rock dust performs better than non-treated rock dust in arresting a propagating explosion, especially in the presence of moisture. |
Floor dust erosion during early stages of coal dust explosion development
Harris ML , Sapko MJ . Int J Min Sci Technol 2019 29 (6) 825-830 An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust. The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply. If the concentration of the dispersed rock dust is sufficient, the flame will stop propagating. Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health (NIOSH) Lake Lynn Experimental Mine (LLEM) to measure the dynamic pressure history and the post-explosion dust scour depth. The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process. This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions. |
Examination of classified rock dust (treated and untreated) performance in a 20-L explosion chamber
Perera IE , Harris ML , Sapko ML . J Loss Prev Process Ind 2019 62 Mine explosions are caused by the ignition of excessive accumulations of combustible dust and/or flammable gas mixed with air in the presence of an ignition source. Rock dusting (limestone dust) is a primary measure to prevent propagating coal dust explosions in underground coal mines in the United States. Although rock dust is considered a nuisance dust, Continuous Personal Dust Monitors (CPDMs) do not distinguish between the coal dust and rock dust and assess the total dust exposure. During application, the <10 μm limestone particles and coal dust particles can become suspended and carried by the ventilating air for long distances and can be measured by the CPDMs. There is a concern in the mining industry that rock dust can be included in the CPDM measurements and make the samples noncompliant. Research conducted by the National Institute for Occupational Safety and Health (NIOSH) has found that all rock dust (RD) cakes after being wetted and then dried. To prevent rock dust from caking, several rock dust manufacturers have developed anti-caking rock dusts. The anti-caking additives used are typically fatty acids that make the rock dust hydrophobic and are added in very low quantities (<1%). While this development will add to the rock dust fluidity, an inevitable problem may be the increased airborne re-entrainment of rock dust due to vehicle movement and foot traffic in the area. Thus, one consideration to reduce such exposure from rock dust is to remove the respirable size fraction (<10 μm) of the applied rock dust. This paper presents the results of experiments that were conducted to determine if a rock dust can still inert a coal dust explosion when the respirable (<10 μm) or inhalable (<20 μm) component of the particle size distribution is removed. Three different untreated rock dusts (untreated A, B, and C) with their treated counterparts (treated A, B, and C) were classified using mechanical sieves into several different-sized fractions, including < 10, 10–20, 20–38, 38–53 and > 75 μm. The relative inerting effectiveness of these size fractions were determined using the United States Bureau of Mines (USBM) 20-L explosion chamber. |
Calibration of the cloud and aerosol spectrometer for coal dust composition and morphology
Barone TL , Hesse E , Seaman CE , Baran AJ , Beck TW , Harris ML , Jaques PA , Lee T , Mischler SE . Adv Powder Technol 2019 30 (9) 1805-1814 The cloud and aerosol spectrometer (CAS) was calibrated to enable CAS sizing of coal dust for studies on flammable dust control. Coal dust sizes were determined by light-scattering theories for irregular particles that account for particle composition and morphology in computing coal dust diameters. Coal dust size computations were compared with test dust that was generated by cyclone separation and air-jet sieving and characterized by aerodynamic particle sizer (APS) and computer-controlled scanning electron microscopy (CCSEM) measurements. For test dust in the range of 0.5–32 μm, coal dust size distributions were consistent with cyclone-separated and sieve-segregated sizes. For the 3–20 μm size range, the coal dust size distribution had a mass median diameter that was 14% larger than that of the APS. This difference was reasonable considering that the basic calibration for glass spheres had 13% uncertainty. For the 20–32 μm and 32–45 μm test dusts, mass median diameters differed from CCSEM measurements by only 4% and 5%, respectively. Overall, the results suggest agreement between test dust sizes and computations for coal dust. Alternatively, using conventional Mie theory computations for spheres, coal dust mass median diameters were 35% and 40% larger than APS and CCSEM measurements, respectively. |
Factors affecting the performance of trickle dusters for preventing explosive dust accumulations in return airways
Sapko MJ , Harris ML , Perera IE , Zlochower IA , Weiss ES . J Loss Prev Process Ind 2019 61 1-7 Correctly applied rock dust can dilute, inert, and mitigate the explosive potential of float coal dust. Trickle dusters are one element of a comprehensive system to help prevent coal dust explosions in underground coal mines. Trickle dusters supply rock dust to inert fine float coal dust in areas where it is commonly deposited, such as the longwall tailgate returns, return airways, pillaring areas, and downwind of belt transfers. Dust deposition studies show that the effectiveness of trickle dusters depends on several key factors. Using multiple orifices, rock dust should be released near the mine roof in the direction of the airflow in order to spread the cloud cross the entry. The rock duster should have a mechanism to break up rock dust agglomerates as they leave the rock duster. The particle size distribution of the limestone rock dust and its airborne concentration should be proportional to the airborne size distribution and concentration of coal dust passing by the trickle duster. Specifically, rock dusts having a greater proportion of <74 microm material are more effective at minimizing downwind zones of explosible mixtures than mostly larger particles. In our testing, rock dusts having more than 95% of <74 microm sized particles were adequately dispersed by trickle dusters. Based on our results, the mass rate of rock dust discharge from the trickle duster should exceed the rate of float coal production by at least a factor of four in order to minimize accumulations of explosible dusts. |
Influence of specific surface area on coal dust explosibility using the 20-L chamber
Zlochower IA , Sapko MJ , Perera IE , Brown CB , Harris ML , Rayyan NS . J Loss Prev Process Ind 2018 54 103-109 The relationship between the explosion inerting effectiveness of rock dusts on coal dusts, as a function of the specific surface area (cm2/g) of each component is examined through the use of 20-L explosion chamber testing. More specifically, a linear relationship is demonstrated for the rock dust to coal dust (or incombustible to combustible) content of such inerted mixtures with the specific surface area of the coal and the inverse of that area of the rock dust. Hence, the inerting effectiveness, defined as above, is more generally linearly dependent on the ratio of the two surface areas. The focus on specific surface areas, particularly of the rock dust, provide supporting data for minimum surface area requirements in addition to the 70% less than 200 mesh requirement specified in 30 CFR 75.2. © 2018 |
Respirable dust: Measured downwind during rock dust application
Harris ML , Organiscak J , Klima S , Perera IE . Min Eng 2017 69 (5) 69-74 The Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health (NIOSH) conducted underground evaluations in an attempt to quantify respirable rock dust generation when using untreated rock dust and rock dust treated with an anticaking additive. Using personal dust monitors, these evaluations measured respirable rock dust levels arising from a flinger-type application of rock dust on rib and roof surfaces. Rock dust with a majority of the respirable component removed was also applied in NIOSH's Bruceton Experimental Mine using a bantam duster. The respirable dust measurements obtained downwind from both of these tests are presented and discussed. This testing did not measure miners' exposure to respirable coal mine dust under acceptable mining practices, but indicates the need for effective continuous administrative controls to be exercised when rock dusting to minimize the measured amount of rock dust in the sampling device. |
Design and development of a dust dispersion chamber to quantify the dispersibility of rock dust
Perera IE , Sapko MJ , Harris ML , Zlochower IA , Weiss ES . J Loss Prev Process Ind 2016 39 7-16 Dispersible rock dust must be applied to the surfaces of entries in underground coal mines in order to inert the coal dust entrained or made airborne during an explosion and prevent propagating explosions. 30 CFR. 75.2 states that ". . . [rock dust particles] when wetted and dried will not cohere to form a cake which will not be dispersed into separate particles by a light blast of air . . ." However, a proper definition or quantification of "light blast of air" is not provided. The National Institute for Occupational Safety and Health (NIOSH) has, consequently, designed a dust dispersion chamber to conduct quantitative laboratory-scale dispersibility experiments as a screening tool for candidate rock dusts. A reproducible pulse of air is injected into the chamber and across a shallow tray of rock dust. The dust dispersed and carried downwind is monitored. The mass loss of the dust tray and the airborne dust measurements determine the relative dispersibility of the dust with respect to a Reference rock dust. This report describes the design and the methodology to evaluate the relative dispersibility of rock dusts with and without anti-caking agents. Further, the results of this study indicate that the dispersibility of rock dusts varies with particle size, type of anti-caking agent used, and with the untapped bulk density. Untreated rock dusts, when wetted and dried forming a cake that was much less dispersible than the reference rock dust used in supporting the 80% total incombustible content rule. |
Particle size and surface area effects on explosibility using a 20-L chamber
Harris ML , Sapko MJ , Zlochower IA , Perera IE , Weiss ES . J Loss Prev Process Ind 2015 37 33-38 The Mine Safety and Health Administration (MSHA) specification for rock dust used in underground coal mines, as defined by 30 CFR 75.2, requires 70% of the material to pass through a 200 mesh sieve (<75 μm). However, in a collection of rock dusts, 47% were found to not meet the criteria. Upon further investigation, it was determined that some of the samples did meet the specification, but were inadequate to render pulverized Pittsburgh coal inert in the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) 20-L chamber. This paper will examine the particle size distributions, specific surface areas (SSA), and the explosion suppression effectiveness of these rock dusts. It will also discuss related findings from other studies, including full-scale results from work performed at the Lake Lynn Experimental Mine. Further, a minimum SSA for effective rock dust will be suggested. |
Participation of large particles in coal dust explosions
Man CK , Harris ML . J Loss Prev Process Ind 2014 27 49-54 Float coal dust is produced during the coal mining process in underground mines. If it is entrained, the float coal dust presents a dangerous explosion hazard to miners when it reaches the minimum explosible concentration and is ignited. However, coal dust can be inerted if properly mixed with generous amounts of pulverized rock dust such as limestone to result in a homogeneous dust mixture with a total incombustible content (TIC) ≥80%. In the United States, it is mandatory for the rock dust to be 100% passing through a 20 mesh (841 micrometers) sieve and 70% or more passing through a 200 mesh (75 micrometers) sieve. Laboratory experiments have been conducted using the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) 20-L and the Fike Corporation 1-m3 explosion chambers. Coal and rock dust samples were prepared by sieving and were used to investigate the effect of particle size on explosibility and inerting effectiveness. The results from both chambers show that large coal particles >60 mesh (>250 micrometers) do not explode/ignite at dust concentrations up to 600 g/m3, and limestone rock dust particles >200 mesh (>75 micrometers) require a significantly higher TIC of 90% to inert Pittsburgh pulverized coal (PPC). This data illustrates the significance of particle size for preventing coal dust explosions and the importance of measuring particle size as well as TIC (which includes moisture as well as incombustibles) to determine the true explosibility of a dust sample. |
H1N1 2009 influenza virus infection during pregnancy in the USA
Jamieson DJ , Honein MA , Rasmussen SA , Williams JL , Swerdlow DL , Biggerstaff MS , Lindstrom S , Louie JK , Christ CM , Bohm SR , Fonseca VP , Ritger KA , Kuhles DJ , Eggers P , Bruce H , Davidson HA , Lutterloh E , Harris ML , Burke C , Cocoros N , Finelli L , Macfarlane KF , Shu B , Olsen SJ , Novel Influenza A Pregnancy Working Group . Lancet 2009 374 (9688) 451-8 BACKGROUND: Pandemic H1N1 2009 influenza virus has been identified as the cause of a widespread outbreak of febrile respiratory infection in the USA and worldwide. We summarised cases of infection with pandemic H1N1 virus in pregnant women identified in the USA during the first month of the present outbreak, and deaths associated with this virus during the first 2 months of the outbreak. METHODS: After initial reports of infection in pregnant women, the US Centers for Disease Control and Prevention (CDC) began systematically collecting additional information about cases and deaths in pregnant women in the USA with pandemic H1N1 virus infection as part of enhanced surveillance. A confirmed case was defined as an acute respiratory illness with laboratory-confirmed pandemic H1N1 virus infection by real-time reverse-transcriptase PCR or viral culture; a probable case was defined as a person with an acute febrile respiratory illness who was positive for influenza A, but negative for H1 and H3. We used population estimates derived from the 2007 census data to calculate rates of admission to hospital and illness. FINDINGS: From April 15 to May 18, 2009, 34 confirmed or probable cases of pandemic H1N1 in pregnant women were reported to CDC from 13 states. 11 (32%) women were admitted to hospital. The estimated rate of admission for pandemic H1N1 influenza virus infection in pregnant women during the first month of the outbreak was higher than it was in the general population (0.32 per 100 000 pregnant women, 95% CI 0.13-0.52 vs 0.076 per 100 000 population at risk, 95% CI 0.07-0.09). Between April 15 and June 16, 2009, six deaths in pregnant women were reported to the CDC; all were in women who had developed pneumonia and subsequent acute respiratory distress syndrome requiring mechanical ventilation. INTERPRETATION: Pregnant women might be at increased risk for complications from pandemic H1N1 virus infection. These data lend support to the present recommendation to promptly treat pregnant women with H1N1 influenza virus infection with anti-influenza drugs. FUNDING: US CDC. |
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