Effect of ignition position on vented hydrogen–air deflagration in a 1 m3 vessel

This study investigates the effect of the ignition position on vented hydrogen-air deflagration in a 1 m³ vessel and evaluates the performance of the commercial computational fluid dynamics (CFD) code FLACS in simulating the vented explosion of hydrogen-air mixtures. First, the differences in the measured pressure-time histories for various ignition locations are presented, and the mechanisms responsible for the generation of different pressure peaks are explained, along with the flame behavior. Secondly, the CFD software FLACS is assessed against the experimental data. The characteristic phenomena of vented explosion are observed for hydrogen-air mixtures ignited at different ignition positions, such as Helmholtz oscillation for front ignition, the interaction between external explosion and combustion inside the vessel for central ignition, and the wall effect for back-wall ignition. Flame-acoustic interaction are observed in all cases, particularly in those of front ignition and very lean hydrogen-air mixtures. The predicted flame behavior agree well with the experimental data in general while the simulated maximum overpressures are larger than the experimental values by a factor of 1.5–2, which is conservative then would lead to a safe design of explosion panels for instance. Not only the flame development during the deflagration was well-simulated for the different ignition locations, but also the correspondence between the pressure transients and flame behavior was also accurately calculated. The comparison of the predicted results with the experimental data shows the performance of FLACS to model vented mixtures of hydrogen with air ignited in a lab scale vessel. However, the experimental scale is often smaller than that used in practical scenarios, such as hydrogen refueling installations. Thus, future large-scale experiments are necessary to assess the performance of FLACS in practical use.     

Self-reported occupational blood exposure among paramedics in Poland: a pilot study

Introduction. Paramedics are at risk of occupational blood exposure, increased by the immediacy of provided treatment. However, the issue has not been acknowledged to date by any research in Europe. Methods. This research aimed at assessing occupational blood exposure among paramedics in Poland. Respondents represented 21 Polish medical institutions. Their participation was voluntary and anonymous. Paramedics were provided with a self-directed job-specific questionnaire adapted to Polish conditions from an original US version. Results. 118 paramedics participated in the study from institutions constituting the National Emergency Medical System in Poland; including ambulance crews, Helicopter Emergency Medical Services and emergency department employees. Occupational exposure was reported by 18.64% of respondents and the main route of exposure was needlestick events. Conclusions. There is a further need to improve education among paramedics concerning the threat of being infected with blood-borne pathogens through all existing routes. Our findings point to the problem as being hidden and considered a shameful issue.     

Large inter annual variation in air quality during the annual festival ‘Diwali' in an Indian megacity

A network of air quality and weather monitoring stations was established under the System of Air Quality Forecasting and Research(SAFAR) project in Delhi. We report observations of ozone(O_3), nitrogen oxides(NO_x), carbon monoxide(CO) and particulate matter(PM_2.5and PM_(10)) before, during and after the Diwali in two consecutive years, i.e., November 2010 and October 2011. The Diwali days are characterised by large firework displays throughout India. The observations show that the background concentrations of particulate matter are between 5 and 10 times the permissible limits in Europe and the United States. During the Diwali-2010, the highest observed PM_(10) and PM_2.5mass concentration is as high as2070 μg/m~3 and 1620 μg/m3, respectively(24 hr mean), which was about 20 and 27 times to National Ambient Air Quality Standards(NAAQS). For Diwali-2011, the increase in PM_(10) and PM_2.5mass concentrations was much less with their peaks of 600 and of 390 μg/m~3 respectively, as compared to the background concentrations. Contrary to previous reports,firework display was not found to strongly influence the NO_x, and O_3 mixing ratios, with the increase within the observed variability in the background. CO mixing ratios showed an increase. We show that the large difference in 2010 and 2011 pollutant concentrations is controlled by weather parameters.     

Thermal runaway reaction for highly exothermic material in safe storage temperature

Highly exothermic materials have caused many serious accidents involving storage and transportation, due to being thermally reactive. The safe storage and management of these materials is still a critical problem in many countries. Our aim was to study the thermal hazard of thermal reactive materials, such as a propellant, by employing differential scanning calorimetry (DSC) non-isothermal tests and isothermal tests, and then comparing the kinetic parameters by isothermal and non-isothermal of kinetics. The chosen approach was to obtain reliable thermal decomposition by a safe and effective method, which acquired the kinetic and safety parameters of storage conditions that could be applied as highly exothermic materials' reduction of loss prevention and energy potential for safer design during storage transport and processing operations.     

Gas explosion analysis of safety gap effect on the innovating FLNG vessel with a cylindrical platform

After investigating gas dispersion on a cylindrical Floating Liquefied Natural Gas (FLNG) platform (Li et al, 2016), this second article focuses on assessment of gas explosion by using Computational Fluid Dynamics (CFD). Gas explosion simulations are carried out to evaluate the explosion overpressure mitigating effect of safety gap. The Data-dump technique, which is an effective tool in resetting turbulence length scale in gas explosion overpressure calculation, is applied to ensure simulation accuracy for the congestion scenario with safety gap. Two sets of different safety gaps are designed to investigate the safety gap on the cylindrical FLNG platform, the overall results indicate that the safety gap is effective in reducing overpressure in two adjacent congestions. However, for the explosion scenario where the flame is propagating through several safety gaps to the far field congestion, the safety gap mitigates overpressure only in certain explosion protecting targets. Two series of artificial configurations are modeled to further investigate the explosion scenarios with more than two safety gaps in one direction. It is concluded that the optimal safety gap design in overpressure mitigation for the cylindrical FLNG platform is to balance the safety gap distance ratio in the congested regions.     

我国循环经济发展路径的思考

通过对EKC理论研究,对我国环境经济指标变化情况进行分析,判断目前发展阶段,对我国发展循环经济模式应采取的措施及有效路径进行了展望。     

城乡基本公共服务均等化评估指标研究——以城乡环境服务领域为例

在界定环境基本公共服务范围的基础上,从安全的饮用水、清洁的大气和城乡污水垃圾治理基础设施3个领域构建了城乡环境基本公共服务均等化评估指标体系,并选取长春、贵阳、广州3个地区进行实证评估.结果表明,该指标体系下,环境基本公共服务领域,城乡均等化水平由高到低依次是广州、长春和贵阳.所构建的指标体系可以对城乡环境基本公共服务均等化水平进行识别和定量评估,评估结果可识别区域内城乡环境基本公共服务均等化过程中存在的问题和关键节点。     

基于环境承载力的适度人口规模研究——以北海市为例

以北海市为例,以环境承载力的几个主要分量作为人口规模的限制因子,分别计算各限制因子约束下的适度人口规模,根据木桶原理,取最小值作为环境承载力约束下的城市适度人口规模。结果表明,能源和大气环境、水资源和土地资源承载力均不会限制人口规模;在不排海情景下,水环境容量明显不足,在排海情景下,COD和NH_3~-N的环境容量对应的适度人口分别为133.05万人和153.72万人,仍无法满足北海市水环境功能要求。北海市的适度人口规模取决于水环境容量,具体在130~150万之间。     

农用地土壤环境分类管理研究

通过分析国内外农用地土壤环境分类管理经验,结合我国土壤环境质量状况,以土壤环境风险管控为主线,将农用地土壤分为优先保护类、安全利用类和严格管控类3个类别,并提出相应的分类管理措施,保障农产品质量安全和人体健康。     

关于土壤环境污染及控制指导值制订问题的探讨

《土壤污染防治行动计划》是国家系统开展土壤污染预防、保护、管控和治理的重大战略部署。文章从污染物来源和土壤污染判断依据两方面探讨了"土壤污染"的概念;提出了我国的"土壤环境污染控制指导值"包括3套指导值,分别为"土壤环境风险筛选值"、"土壤环境修复指导值"和"土壤环境修复启动值",并分析了3套指导值的目标定位、制订策略和执行策略。