Last data update: Jun 24, 2024. (Total: 47078 publications since 2009)
Records 1-12 (of 12 Records) |
Query Trace: Litton CD [original query] |
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Evaluation of detection and response times of fire sensors using an atmospheric monitoring system
Rowland JH 3rd , Litton CD , Thomas RA . Trans Soc Min Metall Explor Inc 2016 340 (1) 104-112 Atmospheric monitoring systems (AMS) are required when using air from conveyor belt entries to ventilate working sections in U.S. underground coal mines. AMS technology has the potential to increase fire safety mine-wide, but research is needed to determine the detection and response times for fires of a variety of combustible materials. To evaluate the potential of an AMS for fire detection in other areas of a coal mine, a series of full-scale fire experiments were conducted to determine detection and response times from fires of different combustible materials that are found in U.S. underground coal mines, including high- and low-volatility coals, conveyor belts, brattice materials, different types of wood, diesel fuel, and a foam sealant. These experiments were conducted in the Safety Research Coal Mine (SRCM) of the U.S. National Institute for Occupational Safety and Health (NIOSH) located in Pittsburgh, PA, using a commercially available AMS that is typical of current technology. The results showed that through proper selection of sensors and their locations, a mine-wide AMS can provide sufficient early fire warning times and improve the health and safety of miners. |
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. |
Determination of the fire hazards of mine materials using a radiant panel
Harteis SP , Litton CD , Thomas RA . Min Eng 2016 68 (1) 40-45 The objective of this study was to develop a laboratory-scale method to rank the ignition and fire hazards of commonly used underground mine materials and to eliminate the need for the expensive large-scale tests that are currently being used. A radiant-panel apparatus was used to determine the materials' relevant thermal characteristics: time to ignition, critical heat flux for ignition, heat of gasification, and mass-loss rate. Three thermal parameters, TRP, TP1 and TP4, were derived from the data, then developed and subsequently used to rank the combined ignition and fire hazards of the combustible materials from low hazard to high hazard. The results compared favorably with the thermal and ignition hazards of similar materials reported in the literature and support this approach as a simpler one for quantifying these combustible hazards. |
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. |
Guest editorial: fire safety in mines
Litton CD . Fire Technol 2015 51 (2) 225-6 Fires in underground mines pose unique problems typically not encountered in other industries. The underground tunnels and entries may be lined with coal or heavily laden with wood for support providing an almost endless supply of fuel while the forced ventilation airflow provides a constant supply of oxygen to fuel the fires that occur while, at the same time, transporting smoke and toxic gases to distances far-removed from the affected fire area. Other fuels exist such as conveyor belts or liquid diesel fuel that may also contribute to the overall fire hazard if consumed as part of a spreading fire. Fires in mines may often be of spontaneous origin when coal is oxidized resulting in self-heating and a smoldering fire that is difficult to prevent and to control. To address these types of fires, Pandey et al. [1] describe the development of chemical retardants that can inhibit, if not prevent, the oxidation and subsequent self-heating of coal. Regardless of the type of fire or combustibles involved, escape-ways and means of egress are often limited placing a high burden on early detection and warning systems in order to rapidly start the evacuation and control measures when fire prevention techniques have not been successful. Understanding the characteristics of the smoke and toxic gases produced can aid in the development of better detection and monitoring systems as well as provide a better understanding of the hazards of toxicity and obscuration that mine fires produce. To aid in this understanding, Perera and Litton [2] discuss the results of experiments to define and quantify the physical and optical properties of aerosols produced from both smoldering and flaming fires from a variety of combustible mine materials. |
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. |
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. |
Development and evaluation of fire barriers to reduce fire hazards on large mining equipment
DeRosa MI , Litton CD . Fire Technol 2013 49 (2) 253-268 The National Institute for Occupational Safety and Health has developed and evaluated various fire barriers for their effectiveness in preventing the spraying of pressurized hydraulic fluids onto simulated turbocharger hot surfaces, and in preventing the ignition of flammable vapors and mists onto barrier outer surfaces. This initial study, however, needs to be followed by a larger investigation that deals with barrier effectiveness in preventing or reducing hydraulic fluid fires within compartments of operating equipment, and barrier physical endurance under hostile environments within compartments. Some of the barriers were also evaluated for their effectiveness in suppressing simulated turbocharger fast-developing fires (initial fires, 32 kW). For the evaluation, modeled engine compartments with simulated turbocharger surfaces of 600A degrees C, initial fires of 32 kW, and a pressurized hydraulic fluid spray system, were used. Also, conceptualized designs of some of the fire barriers, set within the compartments of typical mining equipment, have been reported to provide further guidance toward barrier fabrication and installation. The fire barriers included a parachute silica cloth barrier lined with flexible stainless steel foil; a one-panel insulated stainless steel barrier with a water-spray system; a foldable multi-panel insulated stainless steel barrier; and, an open-close steel strip barrier. Results show that all four fire barriers were effective in preventing the spraying of pressurized hydraulic fluids onto simulated turbocharger hot surfaces. Most of the barriers were also effective in preventing the ignition of flammable vapors and mists onto barrier outer surfaces. Results also show that the parachute barrier and the one-panel barrier with a water-spray system were effective in suppressing simulated turbocharger initial fires of 32 kW. |
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). |
Rapid detection and suppression of mining equipment cab fires
De Rosa MI , Litton CD . Fire Technol 2010 46 (2) 425-435 The National Institute for Occupational Safety and Health (NIOSH/PRL) conducted a series of large-scale experiments to evaluate the effectiveness of optical flame detectors, photoelectric smoke detectors, and combined ionization and photoelectric smoke detectors for rapidly detecting mining equipment cab fires. The detector alarm times were then used to trigger the discharge of a fire inerting system inside the cab to suppress cab material fires. This paper discusses the types of fire detectors tested, the experiments that were conducted, and the results that were obtained. Conclusions are that rapid detection of equipment cab fires can be achieved to trigger the discharge of a fire inerting system inside the cab to protect the operator in the cab. |
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