紫金山登山道主要树种抗火性研究

比较分析了紫金山登山道两侧主要树种的抗火能力,对紫金山不同立地、区位的森林生物防火林带建设和树种选择进行探讨和分析。利用层次分析法,从树种燃烧特性、生物学和生态抗火特性三个方面对紫金山登山道路两侧32种主要树种的抗火性进行综合评价分析,并利用聚类分析对32种树种的抗火性进行分类。结果表明:石楠、油茶、冬青、栓皮栎、青冈、枸骨、麻栎等12种树种综合抗火性较强;朴树、枫香、黄檀、黄连木等7种树种综合抗火性一般;糙叶树、短叶中华石楠、苦树、山胡椒、紫薇、狭叶山胡椒等12种树种综合抗火性较弱;马尾松综合抗火性最弱。树种抗火性评价的11项评价指标中树叶特性、含水率、树皮特征、热值、树冠结构5项指标对树种抗火性影响较大,综合生物学特征对树种抗火性影响最大。冬青、青冈、女贞等常绿大乔木,石楠、油茶、枸骨、茶树等常绿灌木抗火性较强,可以作为防火树种。糙叶树、短叶中华石楠、苦树、山胡椒、紫薇、狭叶山胡椒、瓜木、构树、鸡爪槭、白檀、青桐、卫矛、马尾松等抗火性差,在森林防火中需要重点防护。     

Metallurgical analysis of the ‘cause’ arc beads pattern characteristics under different short-circuit currents

Electric arc beads commonly cause large fire and explosion accidents, especially during the powder process industries. During such fires, the original equipment is often severely burned, rendering electrical fire investigation impossible. Therefore, identifying the beads caused by electrical faults through metallurgical investigation is crucial. This study focused on the ‘cause’ of arc beads and determined their pattern characteristics through metallurgical analysis of copper wires with short-circuit currents of 100, 160, 200, and 240 A. According to microstructure characteristics and metallographic knowledge, bead pattern characteristics were divided into six types: hypereutectic (A), dendritic eutectic (B), chilled layer (C), cellular crystal (D), dendritic (E), and coarse columnar crystal (F). Oxide levels of each category were A (4.5%–7.6%) > C (2.0%–3.8%) > B (1.1%–2.4%) > D (1.0%–2.1%) > E (0.6%–1.9%) > F (0.1%–0.7%). When the short-circuit currents were the same, there were a greater number of small particle beads than large ones. As the current increased, the number of distributed beads with a particle size d < 1 mm decreased, with 1 mm ≤ d < 2 mm increased, and with d ≥ 2 mm were stable. Bead size and distribution had a negative linear correlation at 200 A. When the current increased, the proportion of beads with A and C structures gradually decreased, and those with D structures increased to more than 50%. Oxygen content and arc temperature determined the oxide form. These results are vital for electrical fire investigations and provide theoretical support for fire material evidence extraction and cause identification.     

基于安全等级的地铁车站火灾人员安全疏散方案及其工程应用

地铁火灾安全特别是大型复合地铁车站的火灾安全得到了广泛关注,合理有效的车站人员疏散方案设计是保障地铁车站火灾时人员安全的关键所在.针对地铁车站人员疏散特点,以人员安全疏散准则和现行地铁设计规范为基础,融合了火灾安全工程学的性能化人员疏散设计思路,分别将事故疏散时间和烟控可用安全疏散时间划分为三个等级,综合形成了四类人员疏散安全等级标准,并在此基础上提出了框架性的基于安全等级的地铁车站火灾人员安全疏散方案设计流程.该流程着重采用了自动扶梯反转及列车辅助疏散等措施提高人员的安全性,并结合某大型复合地铁车站的工程案例验证了该疏散方案的可行性.该文的研究工作可为地铁车站人员疏散设计和应急预案制定提供参考.     

钢筋混凝土矩形梁的当量耐火时间

为了正确评估钢筋混凝土矩形梁在实际火灾条件下的承载力,以一般室内火灾轰燃后的房间平均温度一时间曲线为火作用,以热传导和建筑结构耐火理论为基础,以梁在实际和标准火灾下的承载力相等为等效准则,用数值计算方法研究梁的当量耐火时间,并用最小二乘法导出其计算公式.火灾房间火灾荷载越大,开口因子越小,梁的当量耐火时间越长;反之越短.所给梁的当量耐火时间可用于建筑结构性能化耐火设计与评估:当火灾荷载密度较大,开口因子较小时加大梁的截面参数以获得安全性,反之,减小截面参数以获得经济性.     

钢筋混凝土矩形梁在实际火灾下正截面承载力数值计算

为了正确评估钢筋混凝土矩形梁在实际火灾条件下的承载力,以一般室内火灾轰燃后的房间平均温度-时间曲线为火作用,以建筑结构耐火理论为基础,采用数值计算方法研究钢筋混凝土矩形梁的正截面承载力.研究结果表明:梁的承载力随火灾房间温度升高而变小,在温度达到最大值后承载力达到最小值.火灾房间火灾荷载越大,开口因子越小,火作用越大,梁的最小承载力越小;反之相反.相同条件下梁支座截面的承载力要大于跨中截面.     

Fire risk management system for safe operation of large atmospheric storage tanks

This paper has been prepared by its authors to show the benefits coming from the application of the fire risk assessment methodology prepared by the “LastFire^© Project” group of experts. Now a days this methodology seems to be very effective to face the fire risk connected with large atmospheric storage tanks. It has been developed during the period 1997–2005 the HSE & operations experts from experts 16 worldwide operating oil companies. The authors, by “ad hoc” created software package, show the benefit coming from the applications of the LastFire^© methodology and how, from this, using the methodology and the supporting tad, realize a coherent fire strategy in the form of a Fire Risk Management System. Same workflow could also be extended to the issues connected with other problems related with large atmospheric tanks storing hydrocarbons, such as environmental impact by soil pollution, to create a common frame walk of assessment not can be shared with authorities as well. The proposed methodology, moving from the original project, sets as an effective “Fire Hazard Management Approach” in line with the most recent trends (even enforced by the regulations) shared at international levels, that propose the integration of risk assessment with prevention and protection measures selection based on achieved risk reduction, costs, time needed, etc.     

Recovery of Danish coastal dune vegetation after a wildfire

The initial recovery of vegetation after a wildfire in a coastal dune area in NW Jutland, Denmark, was studied over a 5-yr period by means of permanent plots representing various dune communities along a topographical gradient. The impact of the fire varied with the position of the plots. Fens and south-facing dunes were little affected while dune heath plots were severely affected including loss of the O-horizon. Post-fire conditions included presence of remaining soil organic matter, a soil seed bank and surviving below-ground plant parts. The soil surface remained stable during the study period. The initial five years of recovery comprised of an initial three-year recruitment phase during which cover and number of species increased and the quantitative species composition changed markedly, followed by two years of a declining rate of change. 38 species of vascular plants were recorded, 35 are regular components in dune, dune heath and heath fen and were recruited from the seed bank, from locally dispersed seeds and/or by sprouting from surviving vegetative parts. The remaining three species were ‘aliens’, dispersed from sources outside the area. Crustose lichens had an important role in the initial recovery by stabilizing the surface and probably inhibiting seed germination, whereas mosses mostly had a subordinate role. The seral position of the plots, as well as the expected time needed for full recovery of pre-fire vegetation, vary with topography and initial soil conditions. Five years after the fire the fen and the south-facing dune probably need less than a decade for full recovery. The remaining plots are judged to be relatively early seral; their full recovery into mature dry or moist dune heath vegetation and O-horizon is expected to need several centuries.     

Emission and burnt smell characteristics from combustion experiments with defined materials

Typical burnt smell often results from fire accidents or in general from incomplete combustion. Recently, eleven compounds were identified, which are basically responsible for this odour. When analyzing residual materials from different fire accidents, the pattern that means the relative ratios of these compounds among each other varies strongly, although always causing a burnt smelling. Consequently, lab-scale combustion experiments were performed in order to investigate the influence of defined materials from domestic environment on the burnt-smell fingerprints. Furthermore, the occurrence of other polar and higher molecular combustion products was studied. It was found that under good combustion conditions, the burnt smell patterns resulting from the single materials were astonishingly consistent, mostly dominated by methylphenols or naphthalene. No correlation could be found between these ‘fingerprints’ and combustion product groups identified by GC/MS-screenings. LC/MS/MS-measurements especially pointed at the existence of higher molecular weight phenolic and acidic functionalized compounds in the combustion residues.     

Estimating contribution of wildland fires to ambient ozone levels in National Parks in the Sierra Nevada, California

Data from four continuous ozone and weather monitoring sites operated by the National Park Service in Sierra Nevada, California, are used to develop an ozone forecasting model and to estimate the contribution of wildland fires on ambient ozone levels. The analyses of weather and ozone data pointed to the transport of ozone precursors from the Central Valley as an important source of pollution in these National Parks. Comparisons of forecasted and observed values demonstrated that accurate forecasts of next-day hourly ozone levels may be achieved by using a time series model with historic averages, expected local weather and modeled PM values as explanatory variables. Results on fire smoke influence indicated occurrence of significant increases in average ozone levels with increasing fire activity. The overall effect on diurnal ozone values, however, was small when compared with the amount of variability attributed to sources other than fire.     

A comparison between superfine magnesium hydroxide powders and commercial dry powders on fire suppression effectiveness

The effectiveness of superfine magnesium hydroxide powders and commercial dry powder in fire suppression were compared in a laboratory-scale, immovable fire suppression apparatus. The investigation focused on their suppression effectiveness under various pressures. It likewise studied the relationship between the powders’ surface structures and their effectiveness on fire suppression. The microcosmic structure of the powders was observed by scanning electron microscope (SEM), while the Thermal Gravity Analysis (TGA) technique was used to analyze the thermal behavior of the superfine magnesium hydroxide powders. By analyzing the results, it could be concluded that the pressure, the particle size, and the microcosmic structure of the powders’ surface mainly decide the capability of the powders to extinguish the fire. Comparing this with commercial dry powders, superfine magnesium hydroxide powders extinguished the fire in less than 10 s.