Transformations in carbon and nitrogen-forms in peat subjected to progressive thermal stress as revealed by analytical pyrolysis

To study the characteristic N-forms of humic-type materials, samples of sapric peat from Galicia (northern Spain) were heated at 350 °C for 60, 90, 120, 150 and 180 s, and studied by Curie-point Py-GC/MS, solid-state CPMAS ¹³C-NMR and ¹⁵N-NMR spectroscopies. NMR analysis of the peat samples in the progressive heating stages showed the concentration of heterocyclic N-forms, the maximum structural transition amide-to-heterocyclic forms being observed in samples heated for 120 s (56% heterocyclic N and 34% aromatic C). Under more drastic conditions all N-forms were depleted. Correlation between spectroscopic and pyrolytic data betrayed specific pyrolytic markers for the different N-forms. The intensity of the ¹⁵N-NMR amide peak tended to be positively correlated to the yield of indoles, imidazoles and pyrazoles, and negatively correlated to those of benzonitriles and pyrazines. Analytical pyrolysis also showed a progressive enrichment in lipids and alkyl macromolecules with increasing heating intensity, and a decrease in lignin-derived, polysaccharide-derived and N-containing compounds. The relative abundance of non-methoxyphenolic aromatic compounds did not change. The N-compounds in peat samples unheated or heated for 60–90 s released methylpyrazole, dimethylpyrroline, methyldiphenylindole and pyrazole, whereas peat samples heated for 120 s mainly yielded methylpyrazine and methyldiphenylindole. Dimethylpyrroline and pyrazine prevailed in samples heated for 150 s, whereas samples heated for 180 s yielded mainly pyrrole. Pyrolysis data presented low possibilities for forecasting the extent of the O-alkyl domain, but reflected quantitatively the transformations in the lignin-like moiety. Both techniques coincide in pointing out the accumulation of a recalcitrant alkyl domain possibly derived from abiotic condensations or inherited lipid biomacromolecules.     

轨顶排烟口对地铁地下车站火灾排烟效果影响研究

为了研究取消轨顶风口对地铁地下车站火灾防排烟的影响，采用CFD方法，针对全封闭站台门系统和全高站台门系统2种典型地铁车站，模拟车站公共区火灾和车站列车火灾发生时，有无轨顶风口对车站内排烟效果的影响。研究结果表明:针对车站公共区火灾，无论是全封闭站台门还是全高站台门系统，取消轨顶排烟口对公共区烟气温度、可见度、CO浓度等影响较低；但针对车站列车火灾，取消轨顶排烟口对公共区烟气温度、可见度、CO浓度均具有较大影响，排烟效果下降较多。     

Effects of interactions between anthropogenic stressors and recurring perturbations on ecosystem resilience and collapse

Insights into declines in ecosystem resilience and their causes and effects can inform preemptive action to avoid ecosystem collapse and loss of biodiversity, ecosystem services, and human well-being. Empirical studies of ecosystem collapse are rare and hampered by ecosystem complexity, nonlinear and lagged responses, and interactions across scales. We investigated how an anthropogenic stressor could diminish ecosystem resilience to a recurring perturbation by altering a critical ecosystem driver. We studied groundwater-dependent, peat-accumulating, fire-prone wetlands known as upland swamps in southeastern Australia. We hypothesized that underground mining (stressor) reduces resilience of these wetlands to landscape fires (perturbation) by diminishing groundwater, a key ecosystem driver. We monitored soil moisture as an indicator of ecosystem resilience during and after underground mining. After landscape fire, we compared responses of multiple state variables representing ecosystem structure, composition, and function in swamps within the mining footprint with unmined reference swamps. Soil moisture declined without recovery in swamps with mine subsidence (i.e., undermined), but was maintained in reference swamps over 8 years (effect size 1.8). Relative to burned reference swamps, burned undermined swamps showed greater loss of peat via substrate combustion; reduced cover, height, and biomass of regenerating vegetation; reduced postfire plant species richness and abundance; altered plant species composition; increased mortality rates of woody plants; reduced postfire seedling recruitment; and extirpation of a hydrophilic animal. Undermined swamps therefore showed strong symptoms of postfire ecosystem collapse, whereas reference swamps regenerated vigorously. We found that an anthropogenic stressor diminished the resilience of an ecosystem to recurring perturbations, predisposing it to collapse. Avoidance of ecosystem collapse hinges on early diagnosis of mechanisms and preventative risk reduction. It may be possible to delay or ameliorate symptoms of collapse or to restore resilience, but the latter appears unlikely in our study system due to fundamental alteration of a critical ecosystem driver. Efectos de las interacciones entre los estresantes antropogénicos y las perturbaciones recurrentes sobre la resiliencia y el colapso de los ecosistemas     

倾斜巷道内火灾逆流层变化规律数值模拟

为确定矿井火灾时期逆流层长度变化规律,给逃生与救护工作提供参考,以下行通风倾斜巷道为研究对象,建立长80 m、宽4 m、高3.5m拱形巷道模型,通过数值模拟的方法,确定多组火灾工况下烟气逆流层的变化规律.结果表明:巷道入口端风速在0.5～3 m/s增大,烟流逆流层长度随之减小,减小幅度逐渐变缓;火源烟流放散速度在5～25 m/s增大,逆流层长度随之增大,且增加幅度逐渐变缓;人口端风速条件固定为1 m/s,巷道倾角在O°～45°增加,火源烟气放散速度小于18 m/s时,逆流层长度随巷道倾角增加而减小,火源烟气放散速度大于18 m/s时,逆流层长度随巷道倾角增加而增加.     

Combining product engineering and inherent safety to improve the powder impregnation process

The functionalization of nonwoven textiles can be realized by dry powder impregnation. In order to develop and improve this process, two complementary approaches have been combined: product engineering and inherent safety. It consists in integrating ab-initio consumers' requirements, production constraints as well as safety and environmental considerations. This case study is focused on the proposal, the characterization and the selection of powders mixtures of flame retardants and copolyesters, which will be used to create fire-proofed textiles. The influences of the chemical natures of the flame retardant (e.g. calcium carbonate, aluminium trihydroxide, ammonium polyphosphates), their respective concentrations, particle diameters and the addition of silica to flame retardant/polymer mixtures on their minimum ignition energy has been investigated. It has been determined that ammonium polyphosphates are far more efficient than other flame-retardants and that a minimum of 20%wt. concentration is needed to generate a powder mixture that will be almost insensitive to ignition by an electrostatic source. Modifying the particle size distribution and introducing glidants play also a significant role on flame retardant/polymer interactions, on powder dispersibility and has a strong impact on the minimum ignition energy. Finally, the formulations which have been selected fulfill the requirements for fire resistance, flowability, prevention of dust explosion; they are non-toxic, environmentally friendly and their cost is reduced.     

受火后方钢管约束钢筋再生混凝土轴压短柱力学分析

利用ABAQUS软件建立了火灾后方钢管约束钢筋再生混凝土轴压短柱非线性有限元模型,在确定混凝土和钢材的本构基础上,对其火灾后轴压性能进行了数值计算,并与已有相关试验数据进行了对比验证。分析了升温时间、基体混凝土强度、再生粗集料取代率、截面尺寸、含钢率等参数对火灾后轴压性能的影响规律。结果表明:随着升温时间的增加,试件截面角部对中心区域的约束效果逐渐减弱,截面应力逐渐降低且分布趋向均匀;基体混凝土强度和截面直径是影响试件剩余承载力和初始损伤的主要因素,集料取代率和含钢率影响较小,所有试件的损伤发展过程较为相似;各试件的耗能能力随升温时间的增加呈现先提高后降低的趋势;提出了此类试件火灾后相关评价指标的简化计算公式,可为工程实际应用提供参考。     

城市地震火灾风险评估指标体系研究

从多方面系统、全面地研究了城市地震火灾原因及其消防工作。在借鉴民事火灾风险评估指标体系的基础上,结合地震情况下的潜在起火源、城市地震火灾发生的主要原因、城市消防系统在地震火灾的预防及扑救方面所起的作用以及城市环境对地震火灾的影响等因素,建立了城市地震火灾风险评价指标体系。运用专家调查法确定出各指标的相对重要性,采用层次分析法计算出各指标的权重。该项研究为进行城市地震火灾风险评估奠定了理论基础。     

简易喷淋在“三合一”场所消防整治中应用的思考

家庭作坊式或出租屋式的“三合一”场所投资少回报快,成为一些小型私营企业创业初期的首选,但“三合一”场所消防安全条件差火灾频发,尤其是导致人员伤亡的火灾长期高发不下。例举了近年来我国一些“三合一”场所的火灾案例,分析了我国各地采取的“三合一”场所消防安全整治的方法及效果。针对该类场所消防安全整治中难监管、易回潮的特点,提出了在“三合一”场所中推广应用简易自动喷淋系统,革新技防手段的措施,强调了应用简易自动喷淋系统在使用范围、自动报警、喷头选择方面应注意的事项。     

N biogeochemistry and cycling in two well-drained savannas: a comparison between the Orinoco Basin (Llanos,Venezuela) and Ivory Coast (western Africa)

When a savanna burns, a decline in the input of organic matter and nutrients to the soil occurs. However, the existence of recurrent fires is a natural condition and N depletion by fire is not incompatible with the existence of savannas per se. Consequently, savanna vegetations have evolved under fires, implying a near to steady-state N budget. In some Australian and African ecosystems, N fixation appears to be insufficient to replace losses inducing soil-N depletion, whereas in neotropical Llanos and western African savannas, the N-fixation and precipitation seem to be enough to maintain production despite fires. This review presents information about well-drained savannas, namely Trachypogon savannas in Orinoco Llanos and Andropogonae savannas in Ivory Coast. The sites present similarities in climate and fire regime differing in soil parent material. A report on N budgets is presented. The budget was positive, since losses seem to be balanced by inputs in rainfall and biological fixation. Uncertainties in flux measures indicate that more work on those aspects are required. Results indicate that the estimated amounts of dinitrogen fixation and deposition seem to be enough to maintain plant production. Data support the hypothesis that the vegetation in the natural savanna has evolved under fire constraint.     

Concentrations of polycyclic aromatic hydrocarbons in soils of a mangrove forest affected by forest fire

Surface soils affected by forest fires from Igbanko mangrove forest in Nigeria were analyzed for 16 EPA priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography–mass spectrometry (GC–MS). The total PAHs concentrations in the soils ranged from 63 to 188?µg?kg^?1 dry weight (average: 108?µg?kg^?1). The three predominant PAHs in the soils were naphthalene (Na), fluoranthene (Flu), and benzo(b)fluoranthene (BbF). Compared to the control sample (19?µg?kg^?1), elevated PAHs concentrations were observed in the soils, an indication of some level of PAHs contamination. PAHs source diagnostic ratios of Flu/(Flu?+?Pyr) and Ant/(Ant?+?Phe) indicated that the PAHs have a pyrogenic origin which may have resulted from combustion of grass, wood, or coal. An assessment based on Canadian soil quality guidelines indicated that the studied locations do not pose any serious adverse risk on human health.