Last data update: May 06, 2024. (Total: 46732 publications since 2009)
Records 1-17 (of 17 Records) |
Query Trace: Perera IE[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. |
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. |
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 |
Some relevant parameters for assessing fire hazards of combustible mine materials using laboratory scale experiments
Litton CD , Perera IE , Harteis SP , Teacoach KA , DeRosa MI , Thomas RA , Smith AC . Fuel (Lond) 2018 218 306-315 When combustible materials ignite and burn, the potential for fire growth and flame spread represents an obvious hazard, but during these processes of ignition and flaming, other life hazards present themselves and should be included to ensure an effective overall analysis of the relevant fire hazards. In particular, the gases and smoke produced both during the smoldering stages of fires leading to ignition and during the advanced flaming stages of a developing fire serve to contaminate the surrounding atmosphere, potentially producing elevated levels of toxicity and high levels of smoke obscuration that render the environment untenable. In underground mines, these hazards may be exacerbated by the existing forced ventilation that can carry the gases and smoke to locations far-removed from the fire location. Clearly, materials that require high temperatures (above 1400 K) and that exhibit low mass loss during thermal decomposition, or that require high heat fluxes or heat transfer rates to ignite represent less of a hazard than materials that decompose at low temperatures or ignite at low levels of heat flux. In order to define and quantify some possible parameters that can be used to assess these hazards, small-scale laboratory experiments were conducted in a number of configurations to measure: 1) the toxic gases and smoke produced both during non-flaming and flaming combustion; 2) mass loss rates as a function of temperature to determine ease of thermal decomposition; and 3) mass loss rates and times to ignition as a function of incident heat flux. This paper describes the experiments that were conducted, their results, and the development of a set of parameters that could possibly be used to assess the overall fire hazard of combustible materials using small scale laboratory experiments. |
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. |
Evaluation of sensors for mine fire detection using an atmospheric monitoring system
Litton CD , Perera IE . Min Eng 2015 67 (6) 68-75 This report presents the results of experiments to evaluate different types of mine fire sensors in an underground mine environment using a commercially available atmospheric monitoring system. To determine how well carbon monoxide (CO) and smoke sensors respond for purposes of fire detection, experiments were conducted using test fires of different mine combustibles and for both flaming and nonflaming combustion. The experiments were designed to assess the response of fire sensors to different contaminants and different contaminant levels produced from the test fires. The experiments were performed in the Safety Research Coal Mine at the U.S. National Institute for Occupational Safety and Health's Bruceton Research Facility in the presence of an average ventilating air velocity of 1.6 m/s (315 fpm). Five fire sensor stations were located downstream of the test fire at fixed locations, with each sensor station consisting of four sensors: a CO fire sensor and three different smoke sensors, of which two were evaluated by the Mine Safety and Health Administration (MSHA) for intrinsic safety and the third was used extensively in underground mines overseas but not evaluated by MSHA for intrinsic safety. All four sensors were mounted near the center of the entry and in the upper onethird of the entry height. A UL-listed combination ionization and photoelectric smoke sensor was mounted near the roof at the first sensor station and its responses were compared against the responses of the four CO and smoke fire sensors. Sensor response data, contaminant travel times, and the impact of fire on the existing ventilation flow are discussed as they apply to earlywarning fire detection. Of significance in the analysis is the need for performance standards for mine fire sensors in order to provide for consistent and timely early warning of developing fires. |
Quantification of Optical and Physical Properties of Combustion-Generated Carbonaceous Aerosols (<PM2.5) Using Analytical and Microscopic Techniques
Perera IE , Litton CD . Fire Technol 2015 51 (2) 247-269 A series of experiments were conducted to quantify and characterize the optical and physical properties of combustion-generated aerosols during both flaming and smoldering combustion of three materials common to underground minesPittsburgh Seam coal, Styrene Butadiene Rubber (a common mine conveyor belt material), and Douglas-fir woodusing a combination of analytical and gravimetric measurements. Laser photometers were utilized in the experiments for continuous measurement of aerosol mass concentrations and for comparison to measurements made using gravimetric filter samples. The aerosols of interest lie in the size range of tens to a few hundred nanometers, out of range of the standard photometer calibration. To correct for these uncertainties, the photometer mass concentrations were compared to gravimetric samples to determine if consistent correlations existed. The response of a calibrated and modified combination ionization/photoelectric smoke detector was also used. In addition, the responses of this sensor and a similar, prototype ionization/photoelectric sensor, along with discrete angular scattering, total scattering, and total extinction measurements, were used to define in real time the size, morphology, and radiative transfer properties of these differing aerosols that are generally in the form of fractal aggregates. SEM/TEM images were also obtained in order to compare qualitatively the real-time, continuous experimental measurements with the visual microscopic measurements. These data clearly show that significant differences exist between aerosols from flaming and from smoldering combustion and that these differences produce very different scattering and absorption signatures. The data also indicate that ionization/photoelectric sensors can be utilized to measure continuously and in real time aerosol properties over a broad spectrum of applications related to adverse environmental and health effects. |
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. |
Evaluation of smoke and gas sensor responses for fires of common mine combustibles
Perera IE , Litton CD . Trans Soc Min Metall Explor Inc 2014 336 (1) 381-390 Experiments were conducted to evaluate the response characteristics of commercially available gas, smoke, and flame sensors to fires of common combustible mine materials. The experiments were conducted in the large-scale Fire gallery located at the National Institute for Occupational Safety and Health (NIOSH) Lake Lynn Laboratory (LLL) in Fairchance, PA, using Ponderosa Pine, Red Oak, Douglas-fir, high and low volatile coals, PVC and SBR conveyor belt, No. 2 diesel fuel, and diesel exhaust. All the experiments (except those using No. 2 diesel fuel and the diesel exhaust tests) were conducted in a similar manner, with combustible materials heated rapidly by electrical strip heaters producing smoldering fires that quickly transitioned into flaming fires. The sensors included a diffusion-type carbon monoxide (CO) sensor, photoelectric- and ionization-type smoke sensors, a video smoke/flame detector, and an optical flame detector. Simultaneous measurements were obtained for average gas concentrations, smoke mass concentrations, and smoke optical densities in order to quantify the levels of combustion products at the alert and alarm times of the sensors. Because the required sensor alarm levels are 10 ppm and 0.044 m(-1) optical density for CO and smoke sensors, respectively, the different sensor alarms are compared to the time at which the CO and smoke reached these alarm levels (1). In addition, the potential impact of using smoke sensors that have met the performance standards from accredited testing laboratories is also evaluated using the response of an Underwriters' Laboratory (UL)-approved combination photoelectric/ionization smoke detector. The results are discussed relative to fire sensor needs that can have a positive impact on mine fire safety. |
An ultra-trace analysis technique for SF6 using gas chromatography with negative ion chemical ionization mass spectrometry
Jong EC , Macek PV , Perera IE , Luxbacher KD , McNair HM . J Chromatogr Sci 2014 53 (6) 854-9 Sulfur hexafluoride (SF6) is widely used as a tracer gas because of its detectability at low concentrations. This attribute of SF6 allows the quantification of both small-scale flows, such as leakage, and large-scale flows, such as atmospheric currents. SF6's high detection sensitivity also facilitates greater usage efficiency and lower operating cost for tracer deployments by reducing quantity requirements. The detectability of SF6 is produced by its high molecular electronegativity. This property provides a high potential for negative ion formation through electron capture thus naturally translating to selective detection using negative ion chemical ionization mass spectrometry (NCI-MS). This paper investigates the potential of using gas chromatography (GC) with NCI-MS for the detection of SF6. The experimental parameters for an ultra-trace SF6 detection method utilizing minimal customizations of the analytical instrument are detailed. A method for the detection of parts per trillion (ppt) level concentrations of SF6 for the purpose of underground ventilation tracer gas analysis was successfully developed in this study. The method utilized a Shimadzu gas chromatography with negative ion chemical ionization mass spectrometry system equipped with an Agilent J&W HP-porous layer open tubular column coated with an alumina oxide (Al2O3) S column. The method detection limit (MDL) analysis as defined by the Environmental Protection Agency of the tracer data showed the method MDL to be 5.2 ppt. |
Modeling the optical properties of combustion-generated fractal aggregates
Litton CD , Perera IE . Fuel (Lond) 2014 130 215-220 Combustion-generated carbonaceous aerosols are generally in the form of fractal aggregates (FA's) with shapes that vary from long chain-like structures to much more compact, almost spherical structures, depending upon the mode or stoichiometry of the combustion process. Typically, as combustion moves from fuel-lean to fuel-rich, aggregate morphologies change from the former to the latter. Accompanying this change in morphology is a change in the chemistry of the aggregates as the percent of carbon in the aggregates also decreases. These combined changes produce radically different scattering and absorption signatures that define their radiative transfer properties. To improve our ability to predict how these optical properties change, experiments were conducted to measure both the physical and optical properties of these aggregates for both flaming and non-flaming modes of combustion. Using the aggregate property data from these experiments, numerical calculations were then performed using both the discrete dipole approximation (DDA) and the Rayleigh-Debye-Gans (RDG) approximation to generate their characteristic scattering and absorption signatures. This paper presents the experimental results, the comparison of the modeling results with the experimental results and discusses those parameters most important to obtain agreement between the modeling and the experiments. |
Evaluation of criteria for the detection of fires in underground conveyor belt haulageways
Litton CD , Perera IE . Fire Saf J 2012 51 110-119 Large-scale experiments were conducted in an above-ground gallery to simulate typical fires that develop along conveyor belt transport systems within underground coal mines. In the experiments, electrical strip heaters, imbedded ~5 cm below the top surface of a large mass of coal rubble, were used to ignite the coal, producing an open flame. The flaming coal mass subsequently ignited 1.83-m-wide conveyor belts located approximately 0.30 m above the coal surface. Gas samples were drawn through an averaging probe located approximately 20 m downstream of the coal for continuous measurement of CO, CO2, and O2 as the fire progressed through the stages of smoldering coal, flaming coal, and flaming conveyor belt. Also located approximately 20 m from the fire origin and approximately 0.5 m below the roof of the gallery were two commercially available smoke detectors, a light obscuration meter, and a sampling probe for measurement of total mass concentration of smoke particles. Located upstream of the fire origin and also along the wall of the gallery at approximately 14 m and 5 m upstream were two video cameras capable of both smoke and flame detection. During the experiments, alarm times of the smoke detectors and video cameras were measured while the smoke obscuration and total smoke mass were continually measured. Twelve large-scale experiments were conducted using three different types of fire-resistant conveyor belts and four air velocities for each belt. The air velocities spanned the range from 1.0 m/s to 6.9 m/s. The results of these experiments are compared to previous large-scale results obtained using a smaller fire gallery and much narrower (1.07-m) conveyor belts to determine if the fire detection criteria previously developed remained valid for the wider conveyor belts. Although some differences between these and the previous experiments did occur, the results, in general, compare very favorably. Differences are duly noted and their impact on fire detection discussed. |
Impact of air velocity on the detection of fires in conveyor belt haulageways
Perera IE , Litton CD . Fire Technol 2011 48 (2) 405–418 A series of large-scale experiments were conducted in an above-ground fire gallery using three different types of fire-resistant conveyor belts and four air velocities for each belt. The goal of the experiments was to understand and quantify the effects of air velocity on the detection of fires in underground conveyor belt haulageways and to determine the rates of generation of toxic gases and smoke as a fire progresses through the stages of smoldering coal, flaming coal, and finally a flaming conveyor belt. In the experiments, electrical strip heaters, imbedded approximately 5cm below the top surface of a large mass of coal rubble, were used to ignite the coal, producing an open flame. The flaming coal mass subsequently ignited 1.83-m-wide conveyor belts located approximately 0.30m above the coal surface. Gas samples were drawn through an averaging probe for continuous measurement of CO, CO2, and O2 as the fire progressed. Approximately 20m from the fire origin and 0.5m below the roof of the gallery, two commercially available smoke detectors, a light obscuration meter, and a sampling probe for measurement of total mass concentration of smoke particles were placed. Two video cameras were located upstream of the fire origin and along the gallery at about 14m and 5m in order to detect both smoke and flames from the fire. This paper discusses the impact of ventilation airflow on alarm times of the smoke detectors and video cameras, CO levels, smoke optical densities and smoke obscuration, total smoke mass concentrations, and fire heat release rates, examining how these various parameters depend upon air velocity and air quantity, the product of air velocity, and entry cross-section. 2011 Springer Science+Business Media, LLC (Outside the USA). |
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