Critical Analysis of Longwall Ventilation Systems and Removal of Methane

Bleeder systems are an important component for ventilation and the control of methane. The bleeder system of a coal mine contains a mixing zone for methane-laden air from the mined-out portions of the seam to mix with fresh air and the methane concentrations in the bleeders can often be elevated. Bleeders also provides a pathway for coalbed methane-laden ventilation air to quickly flow out of the mine through low resistance airways of a mine, such as supported gateroads, along the un-compacted outer perimeter of the gob, etc. Substantial quantities of coalbed methane are typically removed from underground workings. Although it is a relatively simple task to determine the methane quantities exiting the mine through direct measurements, a clear understanding of the exact manner and associated concentrations in which bleeder entries accumulate and transport methane-air mixtures is not known. The benefit of this improved understanding will decrease the likelihood of an explosion due to unknown accumulations of explosive gases in the bleeder entries, thereby improving worker safety.;In order to provide a better understanding of how a bleeder system works in moving methane through the mine, several field monitoring studies have been designed and completed using a tube bundle system and tracer gas releases. The tube bundle system was installed at a bleederless (progressively sealed) underground coal mine. The tube bundles monitoring points were located at different critical locations surrounding the longwall to specifically monitor gas concentrations and barometric pressures on a 30 minute interval for a period of two years. The tracer gas studies, on the other hand, were conducted at an underground coal operation with a traditional bleeder system. The objectives of these tracer tests were to determine transportation pathways and retention times of tracer gasses to better understand the exact gas movements in longwall gobs. The tracer gas was sampled from different headgate and tailgate entries through sample tubes of different lengths using vacutainers. The gas samples were analyzed using gas chromatography for determining concentration measurements for tracer and other gasses, including methane.;The tube bundle system results showed that falling barometric atmospheric pressure can cause the caved material to outgas higher concentrations of contaminants into the bleeder system. During prolonged atmospheric pressure drops, the gas concentrations leaving the caved material via the bleederless system were measured to increase by over two times the average values. These results strongly suggest that to effectively monitor and detect these outgassing events, the bleeder system requires collecting data more often than the once-a-week regulation stated in the 30 CFR Part §75.364.;The tracer gas testing showed locations of high methane in the bleeders, but the practice in multi panel longwall districts of use premixing of the airflow exiting the longwall panels with cleaner airflow to dilute the methane concentrations to below allowable levels before passing through bleeder evaluation points masked the high methane concentrations. Specifically, samples with methane concentration above 4% were collected from the middle entry of the tailgate, but these airflows were diluted to below 2% just before reaching the bleeder evaluation points, and the mine was unaware of the higher methane levels. This result indicates that premixing of explosive airflow as soon possible, as it exits from the tailgate entries in this case, is beneficial to reducing possible explosions, sampling locations need to be closer to the caved material to better monitor and record the actual conditions existing within the inaccessible bleeder locations.;The explosive mixtures of methane in the bleeder are not theoretical but exist and are measurable with direct and indirect methods within both bleeder and bleederless ventilation system. Obtaining measurements of these mixtures is the first step to be able to better engineer longwall ventilation safety.;The conclusions for this research are: 1) Long duration atmospheric pressure drops of a day or more in length are the controlling factor in increased emission from the caved material. 2) The practice of pre-mixing airflows leaving the middle entries between longwall panels with low methane airflow before reaching the bleeder evaluation points, can mask the existence of explosive mixtures of methane at other locations in the bleeders. 3) Without knowledge of the precise locations of high methane in the bleeder entries, the bleeder system cannot be optimized for minimizing explosive methane concentrations and improve miner safety. To solve the atmospheric pressure drop issue it is recommended that a continuous monitoring system should be installed on surface to record these mine-wide changes in total methane emissions. It is also recommended that bleeder evaluation points should be moved closer to the caved material or the sample tubes should be used to monitor critical locations before mixing occurs. Both of these recommendations will improve the understanding of the nature of gas transportation within the bleeder system and thereby lead to improved worker safety

Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980-2015 : a systematic analysis for the Global Burden of Disease Study 2015

Background Improving survival and extending the longevity of life for all populations requires timely, robust evidence on local mortality levels and trends. The Global Burden of Disease 2015 Study (GBD 2015) provides a comprehensive assessment of all-cause and cause-specific mortality for 249 causes in 195 countries and territories from 1980 to 2015. These results informed an in-depth investigation of observed and expected mortality patterns based on sociodemographic measures. Methods We estimated all-cause mortality by age, sex, geography, and year using an improved analytical approach originally developed for GBD 2013 and GBD 2010. Improvements included refinements to the estimation of child and adult mortality and corresponding uncertainty, parameter selection for under-5 mortality synthesis by spatiotemporal Gaussian process regression, and sibling history data processing. We also expanded the database of vital registration, survey, and census data to 14 294 geography-year datapoints. For GBD 2015, eight causes, including Ebola virus disease, were added to the previous GBD cause list for mortality. We used six modelling approaches to assess cause-specific mortality, with the Cause of Death Ensemble Model (CODEm) generating estimates for most causes. We used a series of novel analyses to systematically quantify the drivers of trends in mortality across geographies. First, we assessed observed and expected levels and trends of cause-specific mortality as they relate to the Socio-demographic Index (SDI), a summary indicator derived from measures of income per capita, educational attainment, and fertility. Second, we examined factors affecting total mortality patterns through a series of counterfactual scenarios, testing the magnitude by which population growth, population age structures, and epidemiological changes contributed to shifts in mortality. Finally, we attributed changes in life expectancy to changes in cause of death. We documented each step of the GBD 2015 estimation processes, as well as data sources, in accordance with Guidelines for Accurate and Transparent Health Estimates Reporting (GATHER). Findings Globally, life expectancy from birth increased from 61.7 years (95% uncertainty interval 61.4-61.9) in 1980 to 71.8 years (71.5-72.2) in 2015. Several countries in sub-Saharan Africa had very large gains in life expectancy from 2005 to 2015, rebounding from an era of exceedingly high loss of life due to HIV/AIDS. At the same time, many geographies saw life expectancy stagnate or decline, particularly for men and in countries with rising mortality from war or interpersonal violence. From 2005 to 2015, male life expectancy in Syria dropped by 11.3 years (3.7-17.4), to 62.6 years (56.5-70.2). Total deaths increased by 4.1% (2.6-5.6) from 2005 to 2015, rising to 55.8 million (54.9 million to 56.6 million) in 2015, but age-standardised death rates fell by 17.0% (15.8-18.1) during this time, underscoring changes in population growth and shifts in global age structures. The result was similar for non-communicable diseases (NCDs), with total deaths from these causes increasing by 14.1% (12.6-16.0) to 39.8 million (39.2 million to 40.5 million) in 2015, whereas age-standardised rates decreased by 13.1% (11.9-14.3). Globally, this mortality pattern emerged for several NCDs, including several types of cancer, ischaemic heart disease, cirrhosis, and Alzheimer's disease and other dementias. By contrast, both total deaths and age-standardised death rates due to communicable, maternal, neonatal, and nutritional conditions significantly declined from 2005 to 2015, gains largely attributable to decreases in mortality rates due to HIV/AIDS (42.1%, 39.1-44.6), malaria (43.1%, 34.7-51.8), neonatal preterm birth complications (29.8%, 24.8-34.9), and maternal disorders (29.1%, 19.3-37.1). Progress was slower for several causes, such as lower respiratory infections and nutritional deficiencies, whereas deaths increased for others, including dengue and drug use disorders. Age-standardised death rates due to injuries significantly declined from 2005 to 2015, yet interpersonal violence and war claimed increasingly more lives in some regions, particularly in the Middle East. In 2015, rotaviral enteritis (rotavirus) was the leading cause of under-5 deaths due to diarrhoea (146 000 deaths, 118 000-183 000) and pneumococcal pneumonia was the leading cause of under-5 deaths due to lower respiratory infections (393 000 deaths, 228 000-532 000), although pathogen-specific mortality varied by region. Globally, the effects of population growth, ageing, and changes in age-standardised death rates substantially differed by cause. Our analyses on the expected associations between cause-specific mortality and SDI show the regular shifts in cause of death composition and population age structure with rising SDI. Country patterns of premature mortality (measured as years of life lost [YLLs]) and how they differ from the level expected on the basis of SDI alone revealed distinct but highly heterogeneous patterns by region and country or territory. Ischaemic heart disease, stroke, and diabetes were among the leading causes of YLLs in most regions, but in many cases, intraregional results sharply diverged for ratios of observed and expected YLLs based on SDI. Communicable, maternal, neonatal, and nutritional diseases caused the most YLLs throughout sub-Saharan Africa, with observed YLLs far exceeding expected YLLs for countries in which malaria or HIV/AIDS remained the leading causes of early death. Interpretation At the global scale, age-specific mortality has steadily improved over the past 35 years; this pattern of general progress continued in the past decade. Progress has been faster in most countries than expected on the basis of development measured by the SDI. Against this background of progress, some countries have seen falls in life expectancy, and age-standardised death rates for some causes are increasing. Despite progress in reducing age-standardised death rates, population growth and ageing mean that the number of deaths from most non-communicable causes are increasing in most countries, putting increased demands on health systems. Copyright (C) The Author(s). Published by Elsevier Ltd.Peer reviewe

Methane emissions and airflow patterns along longwall faces and through bleeder ventilation systems

The Gros-Horloge, built next to the town belfry; Rouen is the former center of the Rotomagi; invaded by Normans in the 9th century; occupied by England 1418-1449. It is the site of trial and execution of Joan of Arc in 1431; taken by Huguenots 1562; held by Germany 1870; site of famous 13th-century Gothic cathedral damaged in World War II. Source: Thesaurus of Geographic Names (Notes) [website]; http://www.getty.edu/research/conducting_research/vocabularies/tgn/ (accessed 7/16/2008