Use of discriminant analysis to predict arson-prone structures

Summary The technique of discriminant analysis is widely used for discriminating arson from nonarson structures. Since in this particular case only two groups are involved viz., the arson and the match groups, the computations required for obtaining a discriminant function are relatively simple. Because of this, it is possible to delete a variable by examining the value of a _i d _i where a _i is the coefficient for the i ^th variable in the discriminant function and d _i is the difference between the means for the arson and the match groups for the i ^th variable (i=1, 2, …, p). Thus, if a _i d _i <0 then we delete the i ^th variable from consideration because inclusion of such a varable, increases the probability of misclassification. A prior knowledge of a _i d _i is particularly useful when we have large numbers of variables to be considered. This will help to reduce the number of discriminant functions one needs to consider in order to arrive at the discriminant function which minimizes the misclassification probability. Frequently, in developing a discriminant function one strives to increase the probability of correct classification. However, this probability reflects two components, viz., the probability of correct classification of known arson structures and the probability of correct classification of known nonarson structures. Even if the overall probability of correct classification is high, it does not necessarily imply, as the illustrations of Boston and New York City indicate, that the resulting discriminant function is also efficient in the sense that more arson cases are correctly classified than the nonarson cases. To this end, a procedure has been suggested to compute the cost of the wrong decision for a discriminant function which can be used to compare the cost of two similar types of discriminant functions. Using the relative cost efficiency criterion, it has been shown that the discriminant function for Newark is more efficient than the discriminant function for either Boston or New York City. Reference: Shiledar Baxi, H., “Use of Discriminant Analysis to Predict Arson-Prone Structures,” Fire Technology, Vol. 20, No. 4, November 1984, p. 17     

The strategies of fire prevention on residential fire in Taipei

Records from Taipei City Fire Department show that age and gender of the victims, housing type, the location of the fire, source of ignition, hour range and residential fire deaths are all related to how and why residential fires occurred in Taipei City. With aids of the prevention strategy on residential fire which includes safety precaution, arson prevention and reinforcement of rescue training and the employment of fire rescue decision-making system, we are able to build hierarchy of prevention strategy to reduce the probability of residential fires and injury and deaths.     

Stack effect of smoke for an old-style apartment in Taiwan

Many existing apartments in Taiwan allow parking of motorcycles on the 1st floor along the arcade. For the purposes of lighting and ventilation, there is an opening in upper of the gates. Taking motorcycle arson as a fire scenario, this study proved that smoke would move into the building quickly via the opening and flow upward through the staircases, posing a serious risk whenever motorcycle arson was committed. The simulation results from FDS demonstrated that the visibility decline is very fast inside staircase. When the opening was moved to the bottom of the gate, the decline became slow because the stack effect phenomenon was effectively diminished. Image-recording and laser smoke layer measurement equipment was used to measure smoke diffusion, referring to the Australian Standard, AS 4391-1999 “Smoke management systems-Hot smoke test”. The experiments were executed in a five-story building by recording visibility at a height of 1.8 m on each floor. The results indicated the same conclusions when the opening was moved to the bottom of the gate. The results also verified that the door in the attic staircase was open; the stack effect was very significant.     

吸附管/气相色谱/质谱法分析纵火案的纵火剂残留物

用吸附管(AT)/气相色谱(GC)/质谱(MS)法检测纵火残留物中轻质矿物油是通过吸附管动态吸附检材中可挥发的有机物,然后通过热脱附将挥发物送至GC及GC/MS中检测。它既适用于轻组分的碳氢化合物,如汽油,也适用于较高分子的碳氢化合物,如柴油和煤油。用沸石预处理样品克服了样品中水分对鉴定的干扰。用本方法能够得到比过去所使用的溶剂提取法或顶空法(HS)更高的吸附效率和灵敏度,解决以往由于残留物中热解产物干扰所造成的GC图形混乱复杂,难以准确分析鉴定的问题。用本方法分析纵火或火灾案件中常见的残留物——轻质矿物油,具有快速、灵敏、准确和简便等特点,可广泛用于公安、司法和保险等各个领域。     

用GC-MS方法分析识别汽油类火案引燃物

用30m长、内径0 25mm、DB-5MS普通商用柱,EI源,不分流进样,程序升温,NIST数据库及质量色谱等最通用规范的GC MS基本功能,建立了4种不同产地及不同品种汽油的GC MS图库。高效分离条件下,这些谱图的区别很明显,可直接从碳数分布,C6～12直链烃含量及直、支、环、烯、芳烃相对比例区分对比不同的汽油。立足于GC MS的通用性,强调高效分离及定量的准确性,保证数据可重复性,为全国范围内火案引燃物各厂家GC MS仪器间的对比破案,提供了共用数据平台。