Prediction of Upward Flame Spread over Polymers

In this work, the existing understanding of flame spread dynamics is enhanced through an extensive study of the heat transfer from flames spreading vertically upwards across 5 cm wide, 20 cm tall samples of extruded Poly (Methyl Methacrylate) (PMMA). These experiments have provided highly spatially resolved measurements of flame to surface heat flux and material burning rate at the critical length scale of interest, with a level of accuracy and detail unmatched by previous empirical or computational studies. Using these measurements, a wall flame model was developed that describes a flame’s heat feedback profile (both in the continuous flame region and the thermal plume above) solely as a function of material burning rate. Additional experiments were conducted to measure flame heat flux and sample mass loss rate as flames spread vertically upwards over the surface of seven other commonly used polymers, two of which are glass reinforced composite materials. Using these measurements, our wall flame model has been generalized such that it can predict heat feedback from flames supported by a wide range of materials. For the seven materials tested here – which present a varied range of burning behaviors including dripping, polymer melt flow, sample burnout, and heavy soot formation – model-predicted flame heat flux has been shown to match experimental measurements (taken across the full length of the flame) with an average accuracy of 3.9 kW m-2 (approximately 10 – 15 % of peak measured flame heat flux). This flame model has since been coupled with a powerful solid phase pyrolysis solver, ThermaKin2D, which computes the transient rate of gaseous fuel production of constituents of a pyrolyzing solid in response to an external heat flux, based on fundamental physical and chemical properties. Together, this unified model captures the two fundamental controlling mechanisms of upward flame spread – gas phase flame heat transfer and solid phase material degradation. This has enabled simulations of flame spread dynamics with a reasonable computational cost and accuracy beyond that of current models. This unified model of material degradation provides the framework to quantitatively study material burning behavior in response to a wide range of common fire scenarios.

Effect of ambient pressure and radiation reabsorption of atmosphere on the flame spreading over thermally thin combustibles in microgravity

For the flame spread over thermally thin combustibles in an atmosphere, if the atmosphere cannot emit and absorb the thermal radiation (e.g. for atmosphere Of O-2-N-2), the conductive heat transfer from the flame to the fuel surface dominates the flame spread at lower ambient atmosphere. As the ambient pressure increases, the flame spread rate increases, and the radiant heat transfer from the flame to the fuel surface gradually becomes the dominant driving force for the flame spread. In contrast, if the atmosphere is able to emit and absorb the thermal radiation (e.g. for atmosphere Of O-2-CO2), at lower pressure, the heat transfer from flame to the fuel surface is enhanced by the radiation reabsorption of the atmosphere at the leading edge of the flame, and both conduction and thermal radiation play important roles in the mechanism of flame spread. With the increase in ambient pressure, the oxygen diffuses more quickly from ambient atmosphere into the flame, the chemical reaction in the flame is enhanced, and the flame spread rate increases. When the ambient pressure is greater than a critical value, the thermal radiation from the flame to the solid surface is hampered by the radiation reabsorption of ambient atmosphere with the further increase in ambient pressure. As a result, with the increase in ambient pressure, the flame spread rate decreases and the heat conduction gradually dominates the flame spread over the fuel surface.

Spread across liquids.

Mode of access: Internet.

Laboratory Test Methods For The Evaluation Of Flammability Of Polymers

Combustion is a complex phenomena involving a multiplicity of variables. Some important variables measured in flame tests follow [1]. In order to characterize ignition, such related parameters as ignition time, ease of ignition, flash ignition temperature, and self-ignition temperature are measured. For studying the propagation of the flame, parameters such as distance burned or charred, area of flame spread, time of flame spread, burning rate, charred or melted area, and fire endurance are measured. Smoke characteristics are studied by determining such parameters as specific optical density, maximum specific optical density, time of occurrence of the densities, maximum rate of density increase, visual obscuration time, and smoke obscuration index. In addition to the above variables, there are a number of specific properties of the combustible system which could be measured. These are soot formation, toxicity of combustion gases, heat of combustion, dripping phenomena during the burning of thermoplastics, afterglow, flame intensity, fuel contribution, visual characteristics, limiting oxygen concentration (OI), products of pyrolysis and combustion, and so forth. A multitude of flammability tests measuring one or more of these properties have been developed [2]. Admittedly, no one small scale test is adequate to mimic or assess the performance of a plastic in a real fire situation. The conditions are much too complicated [3, 4]. Some conceptual problems associated with flammability testing of polymers have been reviewed [5, 6].

不同重力下窄通道内薄材料表面的火焰传播

在常重力下模拟微重力燃烧对载人航天器的火灾安全具有重要意义。窄通道就是这样一种可以有效限制自然对流的模拟设施。但是，不同重力下火焰传播的相似性仍然是有待研究的问题。本文用实验和数值模拟的方法，比较了不同重力下有限空间内热薄材料表面的逆风传播火焰。不同重力下火焰形状和火焰传播速度的比较表明，1cm高的水平窄通道可以有效地限制自然对流，在常重力下用这种通道能够模拟微重力下相同几何尺寸的通道中的火焰传播。因此，在地面上首先利用水平窄通道，模拟相同环境中的微重力火焰传播，然后考虑通道尺寸变化对火焰传播的影响，有可能成为地面模拟其他尺寸的空间中的微重力燃烧的方法。

微重力下薄燃料表面火焰传播的地面窄通道模拟

对微重力下薄燃料表面逆风火焰传播的地面窄通道模拟,进行了量纲分析,并通过火焰传播图像记录进行了实验验证.结果表明,减小实验段特征尺寸可以实现微重力燃烧的地面模拟.在各种氧气浓度条件下,竖直和水平窄通道内的火焰传播速度随气流速度的变化趋势完全不同,而且,水平窄通道可以有效限制自然对流,而竖直窄通道较难.当通道高度增大时,竖直和水平窄通道中,火焰传播速度和吹熄极限速度都不同程度地增大,这是热损失减小、火焰面遇见的气流速度减小以及自然对流速度增大3个因素的综合结果.对于水平窄通道, 1 cm是一个可以定性模拟微重力下自然对流的尺寸.对于竖直窄通道,则需要高度更小的窄通道来限制自然对流.

窄通道内热厚材料表面火焰传播的实验研究

利用高度为14 mm的水平窄通道对微重力条件下聚甲基丙烯酸甲酯(PMMA)和聚乙烯(PE)塑料材料表面的火焰传播进行了地面实验模拟研究. 在环境气体氧气浓度为30％和50％、低速气流速度小于15 cm/s的实验条件下, 实验测量了窄通道内材料表面火焰传播速度随气流速度的变化, 它们与微重力下热厚材料火焰传播速度的理论预测结果符合得相当好. 分析认为, 窄通道能够有效地限制浮力对流, 提高燃料表面固相热辐射在火焰传播中的相对作用, 从而提供模拟微重力下热厚材料表面火焰传播特性的实验环境

热薄材料表面火焰传播的三维效应

利用能够限制自然对流的水平窄通道, 对薄材料表面逆风传播火焰的三维效应进行了实验研究, 参数包括气流速度、氧气浓度、燃料宽度等.结果表明, 在足够宽的通道内, 火焰传播随燃料宽度的变化, 表现出随氧气浓度和气流速度的不同而变化的三维特性.侧面热损失和氧气扩散对火焰传播的影响, 在各种氧气浓度和气流速度下, 都限于燃料宽度小于10倍扩散长度

Coupled fire/evacuation analysis of the Station Nightclub fire

In this paper, coupled fire and evacuation simulation tools are used to simulate the Station Nightclub fire. This study differs from the analysis conducted by NIST in three key areas; (1)an enhanced flame spread model and (2)a toxicity generation model are used, (3)the evacuation is coupled to the fire simulation. Predicted early burning locations in the full-scale fire simulation are in line with photographic evidence and the predicted onset of flashover is similar to that produced by NIST. However, it is suggested that both predictions of the flashover time are approximately 15 sec earlier than actually occurred. Three evacuation scenarios are then considered, two of which are coupled with the fire simulation. The coupled fire and evacuation simulation suggests that 180 fatalities result from a building population of 460. With a 15 sec delay in the fire timeline, the evacuation simulation produces 84 fatalities which are in good agreement with actual number of fatalities. An important observation resulting from this work is that traditional fire engineering ASET/RSET calculations which do not couple the fire and evacuation simulations have the potential to be considerably over optimistic in terms of the level of safety achieved by building designs.

FIRES : Fire Information Retrieval and Evaluation System : a program for fire danger rating analysis /

"August 1997."

The distribution and spread of citrus canker in Emerald, Australia

Citrus canker is a disease of citrus and closely related species, caused by the bacterium Xanthomonas citri subsp. citri. This disease, previously exotic to Australia, was detected on a single farm [infested premise-1, (IP1). IP is the terminology used in official biosecurity protocols to describe a locality at which an exotic plant pest has been confirmed or is presumed to exist. IP are numbered sequentially as they are detected] in Emerald, Queensland in July 2004. During the following 10 months the disease was subsequently detected on two other farms (IP2 and IP3) within the same area and studies indicated the disease first occurred on IP1 and spread to IP2 and IP3. The oldest, naturally infected plant tissue observed on any of these farms indicated the disease was present on IP1 for several months before detection and established on IP2 and IP3 during the second quarter (i.e. autumn) 2004. Transect studies on some IP1 blocks showed disease incidences ranged between 52 and 100% (trees infected). This contrasted to very low disease incidence, less than 4% of trees within a block, on IP2 and IP3. The mechanisms proposed for disease spread within blocks include weather-assisted dispersal of the bacterium (e.g. wind-driven rain) and movement of contaminated farm equipment, in particular by pivot irrigator towers via mechanical damage in combination with abundant water. Spread between blocks on IP2 was attributed to movement of contaminated farm equipment and/or people. Epidemiology results suggest: (i) successive surveillance rounds increase the likelihood of disease detection; (ii) surveillance sensitivity is affected by tree size; and (iii) individual destruction zones (for the purpose of eradication) could be determined using disease incidence and severity data rather than a predefined set area.

Gender inequality and the spread of HIV-AIDS in India

Purpose The purpose of the paper is to analyze the low status of women as being a major contributor for the observed gender inequality in the spread of HIV/AIDS in India. Design/methodology/approach The paper uses data from National Aids Control Organization (NACO), National Family Health Survey (NFHS 3), and the Directorate of Economics and Statistics. Findings This study highlights the problems facing women in deterring the spread of HIV/AIDS in India. The status and empowerment of women are important variables in combating the disease among both men and women in India. Literacy, education, exposure to the media, labor market participation, awareness of HIV/AIDS, and economic independence are important considerations in improving the status of women in India. Policymakers need to focus on gender inequality in order to combat the spread of HIV/AIDS in India. Originality/value While absolute figures indicate men are more likely to be infected with HIV/AIDS, the rate of decline is higher for men compared to women in India. We explore several plausible explanations for such observed inequality in the spread of HIV/AIDS across gender. In particular, a potentially important factor - the low status of women in society is attributable as an impediment to the spread of the disease. A case study of the relationship between gender empowerment and the spread of HIV/AIDS in the state with the highest concentration, Manipur, provides more insight to the difficulties faced by women in combating HIV/AIDS in India.