Fire debris analysis by Raman spectroscopy and chemometrics

A paper reporting the use of Raman spectroscopy in fire debris analysis is presented. Five polymer based samples, namely carpet (polypropylene), nylon stockings (nylon), foam packaging (polystyrene), CD cases (polystyrene) and DVD cases (polypropylene) were burnt with each one of the following ignitable liquids: petrol, diesel, kerosene and ethanol. Raman shifts were obtained and, in some cases, peaks were identified to correspond to pyrolysis products in the form of alkanes, aromatic or polyaromatic compounds. All pyrolysis peaks were used to produce a Principal Component Analysis (PCA) of the burned samples with the different ignitable liquids. The change in the Raman spectra made it possible to identify some of the pyrolysis products produced in the combustion and also to identify the different plastic materials in fire debris, even when different fuels have been used and the chemical and structural identity of the plastic has been altered in the fire.     

The burning rate’s effect on the flame length of weak fire whirls

This paper discusses why the visibly-determined flame length of a weak fire whirl increases as compared with the corresponding pool fire without spin. Here, a fire whirl is called weak when the pure aerodynamic effect of flow circulation has a negligible influence on the flame length. Split cylinders were used to apply a flow circulation to a 3-cm-diameter methane burner flame and a 3-cm-diameter ethanol pool fire. After applying the flow circulation, the flame length of the ethanol pool fire increased about three times, while little change was observed in the flame length of the methane burner flame. The difference is explained by the fact that the burning rate of the methane burner flame was fixed constant, whereas that of the ethanol pool fire increased due to the increased heat input to the fuel surface caused by a change in flame shape pushed toward the fuel surface. The experimental observations thus demonstrate that the burning-rate effect can significantly increase the flame length even under a weak circulation condition. Computational fluid dynamics (CFD) simulations were conducted to understand the detailed flow structure of a fire whirl. An analytical model was then developed based on the experimental observations and CFD calculations; the predicted relationship between the flame height and the burning rate agreed with experimental data.     

基于GF-4PMI数据的亮温差校正火点检测方法研究

高分四号PMI可为防灾减灾提供稳定数据,其搭载的中红外传感器可以很好地应用于快速火灾监测中。但由于缺少传统火灾监测的热红外波段,高分四号提供的光谱信息大多作为灾中监测的辅助数据,且现有的火点识别研究所构建的火点自适应阈值检测算法受单一波段的影响,错检率和漏检率均偏高。为进一步探究高分四号数据在林火监测中的应用方法,提高火点识别精度,本研究分析高分四号数据的特点,结合单通道红外光谱的火点监测方法,应用上下文思想提出一种基于双时相影像的亮温差校正火点检测的方法来进一步提高检测精度。该方法使用灾前和灾中两期影像,具体分为时间尺度上基于空间插值的亮温补偿获取,空间尺度上的上下文自适应阈值分割以及火点判识三个部分。首先将两期影像做差值处理,并将潜在火点周围动态邻域内其他无污染像元的亮温差作为采样点进行空间插值,随后将插值结果带入灾前影像中得到灾中未发生火灾时的背景亮温,最后利用判别条件进行火点判别和虚警剔除,得到最终火点检测结果。其中在灾中背景亮温的预测研究对比了反距离加权插值(inverse distance weigh)、简单克里金插值(simple kriging)和普通克里金插值(ordinary kriging)三种插值方法,从拟合结果来看普通克里金插值既体现了像素区域的波动性又有一定的平滑效果避免峰值过高,是较为理想的拟合结果。实验以目视解译的火点数据为参照验证了山西沁源县和内蒙古呼伦贝尔新巴尔虎左旗地区的两起火灾,对比最新提出的单时相火点检测算法,研究结果表明引进的亮温差校正数据可以更好地拟合背景亮温,减少错分误差至3%,并保持综合评价指标F_β分数在0.9以上。该方法有效结合了高分四号空间和时间的信息,未来可用于高分四号PMI数据自动化火点检测与快速提取。     

Modeling of pedestrian evacuation under fire emergency based on an extended heterogeneous lattice gas model

An extended heterogeneous lattice gas (E-HLG) model is developed by introducing an altitude factor into the heterogeneous lattice gas (HLG) model. The altitude factor is used to describe the position height of lattice sites. Evacuation features from a terrace classroom are investigated through simulations using both the model and experiments. To study evacuation processes under fire emergency, an agent-based fire and pedestrian interaction (FPI) model is proposed. It is supposed that the possible moving directions of a pedestrian depend on the environmental temperature field, which is simulated by the software FDS. The walking speed reduction due to the visibility worsening in the FPI model is described by a multi-grid method. It is found that simulation results based on the extended HLG model are in good agreement with the experiments. The altitude factor plays a guidance role to the evacuation, and the fire notably delays the evacuation due to both the harmfulness of the high temperature field and the change of evacuation routes which results in frequent local jamming and clogging.     

基于多源卫星多光谱遥感数据的过火面积估算研究

露天生物质燃烧是重要的大气污染物排放源,导致空气质量恶化并引起气候变化。卫星遥感数据能够提供大尺度、多时相的监测信息,然而燃烧火点监测和火烧迹地监测两种方式都存在着局限性。以美国东南部地区为研究区域,通过结合卫星遥感获取的高分辨率燃烧面积数据及多时相的燃烧火点数据,建立时空匹配模型估算露天生物质燃烧过火面积。通过分析植被燃烧前后的光谱变化特征,基于高分辨率的Landsat-5 TM4波段(0.84 μm)与7波段(2.22 μm)数据, 利用差分归一化燃烧比(dNBR: the differential normalized burn ratio)提取燃烧面积数据;而燃烧火点数据则通过分析燃烧植被的热红外光谱特征利用MODIS 4与11 μm波段数据提取。结果显示,该地区燃烧面积与燃烧火点数量之间相关系数达0.63,并且二者之间的比例关系随植被类型而发生变化,林地、草地、灌木、耕地和沼泽五种植被类型对应的像元燃烧面积分别为0.69,1.27,0.86,0.72和0.94 km2。通过与美国火灾中心(national interagency fire center, NIFC)地面调查数据比对,模型估算的美国东南部过火面积数据较为精确,而同期的MODIS燃烧面积产品(MCD45)及燃烧源清单产品(global fire emissions database, GFED)遗漏了该区域大量的小面积燃烧事件。因此,本研究建立的过火面积估算模型能够提供更为精确的排放源参数信息,有利于区域空气质量模式准确地模拟露天生物质燃烧排放状况。     

The effects of intralayer metal composition of layered double hydroxides on glass transition, dispersion, thermal and fire properties of their PMMA nanocomposites

A series of aluminum-containing layered double hydroxides (LDHs), containing Mg, Ca, Co, Ni, Cu and Zn as the divalent metals, have been prepared by the co-precipitation method and used to prepare nanocomposites of PMMA by in situ bulk polymerization. The additives were characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy (XRD) and thermogravimetric analysis while the polymer composites were characterized by XRD, transmission electron microscopy, differential scanning calorimetry and cone calorimetry. Polymerization of methyl methacrylate in the presence of these undecenoate LDHs results in composites with enhanced thermal stability. The glass transition temperatures of the composites and the pristine polymers are found to be around 110 °C; this suggests that the presence of these additives has little effect on the polymer. It is found that the additive composition and the dispersion state of LDHs agglomerates in the polymer matrix influence the fire properties of composites as measured by cone calorimetry.     

Structure-property relationships of new polystyrene nanocomposites prepared from initiator-containing layered double hydroxides of zinc aluminum and magnesium aluminum

Polystyrene/layered double hydroxides (PS/LDHs) nanocomposites were prepared by free radical polymerization of styrene monomer in the presence of LDHs intercalated with 4,4′-azobis(4-cyanopentanoate) anions (LDH-ACPA). XRD and ATR-IR are used to confirm that the materials produced are layered and the presence of the azo-initiator anions in these LDHs. These LDHs were used successfully to polymerize styrene and both XRD and TEM images of the composites support the formation of a mixed exfoliated-intercalated nanocomposite for ZnAl-ACPA but a microcomposite for MgAl-ACPA. The magnesium-containing LDHs decreased the glass transition temperature (T_g) of the composites while ZnAl-ACPA did not affect T_g significantly. The T_g depression is related to enhanced polymer dynamics due to the extra free volume at the LDH additive-polymer interface. A reduction in the onset of thermal decomposition temperature was observed in PS/LDH compared to neat PS, likely due to the early decomposition of the LDH. The fire performance, as evaluated by the cone calorimeter, reveal that PS-ZnAl-ACPA shows enhanced fire properties compared to PS-MgAl-ACPA.     

The fire retardant behaviour of huntite and hydromagnesite - A review

Naturally occurring mixtures of hydromagnesite and huntite have found important industrial use. Their endothermic decomposition over a temperature range similar to that of commonly used polymers and their release of water and carbon dioxide, has led to such mixtures being successfully used as fire retardants. They have replaced aluminium hydroxide and magnesium hydroxide in many applications. The current understanding of the thermal decomposition mechanism of both minerals and their combination in natural mixtures has been reviewed and related to their fire retardant action. Both minerals contribute to the reduction in flammability of polymers although the extent of these interactions has not been fully investigated. However, the fire retardant mechanism of these minerals appears more complicated than either aluminium hydroxide or magnesium hydroxide.     

Magnetic material in head, thorax, and abdomen of Solenopsis substituta ants: a ferromagnetic resonance study

Ferromagnetic resonance temperature dependence is used to study the magnetic material in smashed head, thorax, and abdomen of Solenopsis substituta ants. These three body parts present the five lines previously observed in other social insects. The magnetic material content is slightly higher in heads with antennae than in abdomen with petiole. Isolated nanoparticle diameters were estimated as 12.5 +/- 0.1 and 11.0 +/- 0.2 nm in abdomen with petiole and head with antennae, respectively. The presence of linear chains of these particles or large ellipsoidal particles are suggested. A bulk-like magnetite particle was observed in the thorax. The Curie-Weiss, the structural-electronic and ordering transition temperatures were obtained in good agreement with those proposed for magnetite nanoparticles.     

Synthesis and combined properties of novel fluorinated cationic surfactants derived from hexafluoropropylene dimer

Three novel fluorinated surfactants with branched short fluorinated tails as hydrophobic groups, ammonium oxide as polar groups are prepared. Surface tension measurement shows that these fluorinated surfactants are ideal compounds to design new formulations in fire-fighting field.