UN test O.1 errors in quantifying the behavior of solid oxidizers

The results of the UN test O.1 for oxidizing solids are shown to be incorrect when specimens contain certain inertant additives, illustrated for the case of oxidizers in the ammonium nitrate fertilizer family. Test results for three different AN-based products containing inertants show that two of the three (including calcium ammonium nitrate, CAN, a long-known safer alternative to AN) would be misranked with the O.1 test. An analogy between the heat release rate of substances containing fire retardant (FR) chemicals is established and several ways by which FR behavior can be achieved are demonstrated. It is shown that the O.1 test implicitly adopts only one model of inertant action, and that chemicals which rely on a differing mode of inertant action are liable to be incorrectly treated. It is further shown that the physical basis of the O.1 test—an intimate mixture of finely-comminuted fuel and oxidizer—misrepresents the most common type of accidents involving oxidizers, and that such test results do not correspond to scenarios of a less extreme nature. The new O.3 test improves the analysis method, but does not resolve the problem of excessive commingling of fuel into oxidizer. It is recommended that the intermediate-scale arrangement used by the Bureau of Explosives be adopted for further development and standardization, in preference to the O.1 or O.3 test arrangements.     

High efficiency of the NH4H2PO4/Mg(OH)2 composite for guaranteeing safety of wood production

Currently, China's timber industry is in high demand with the development of real estate. However, there is a certain fire hazard in the production process of wood manufacturing. Once a fire occurs, the fire is violent and the spread is rapid. Therefore, to improve the safety of its production process, ammonium dihydrogen phosphate and magnesium hydroxide were selected to prepare a new composite superfine dry powder, which was denoted as the NH₄H₂PO₄/Mg(OH)₂ composite. Furthermore, to figure out dry powders' extinction effect on Class A fire, the wood-crib fire suppression effect of the NH₄H₂PO₄/Mg(OH)₂ composite was test, and then compared with that of ultrafine dry powder (UDP) and commercial ABC dry powder (C-ABC) in a 1 m³ chamber. Three parameters of the fire extinguishing process, namely flame extinction time, powder consumption and temperature drop were adopted to measure the fire suppression performance. The results demonstrated that UDP and C-ABC both had a larger flame extinction time and powder consumption than the NH₄H₂PO₄/Mg(OH)₂ composite. Besides, a fire (wood cribs) can be extinguished by the NH₄H₂PO₄/Mg(OH)₂ composite with the fastest temperature drop and a much-improved toxic gas suppression ability. In short, the NH₄H₂PO₄/Mg(OH)₂ composite can better guarantee the safety of the wood processing production process. Moreover, the reasons for performance advantages of the NH₄H₂PO₄/Mg(OH)₂ composite were discussed.     

Evaluation of CFD simulations of transient pool fire burning rates

Fire is the most commonly occurring major accident hazard in the chemical and process industries, with industry accident statistics highlighting the liquid pool fire as the most frequent fire event. Modelling of such phenomena feeds heavily into industry risk assessment and consequence analyses. Traditional simple empirical equations cannot account for the full range of factors influencing pool fire behaviour or increasingly complex plant design. The use of Computational Fluid Dynamics (CFD) modelling enables a greater understanding of pool fire behaviour to be gained numerically and provides the capability to deal with complex scenarios.This paper presents an evaluation of the Fire Dynamics Simulator (FDS) for predictive modelling of liquid pool fire burning rates. Specifically, the work examines the ability of the model to predict temporal variations in the burning rate of open atmosphere pool fires. Fires ranging from 0.4 to 4 m in diameter, involving ethanol and a range of liquid hydrocarbons as fuels, are considered and comparisons of predicted fuel mass loss rates are compared to experimental measurements.The results show that the liquid pyrolysis sub-model in FDS gives consistent model performance for fully predictive modelling of liquid pool fire burning rates, particularly during quasi-steady burning. However, the model falls short of predicting the subtleties associated with each phase of the transient burning process, failing to reliably predict fuel mass loss rates during fire growth and extinction. The results suggest a range of model modifications which could lead to improved prediction of the transient fire growth and extinction phases of burning for liquid pool fires, specifically, investigation of: ignition modelling techniques for high boiling temperature liquid fuels; a combustion regime combining both infinite and finite-rate chemistry; a solution method which accounts for two- or three-dimensional heat conduction effects in the liquid-phase; alternative surrogate fuel compositions for multi-component hydrocarbon fuels; and modification of the solution procedure used at the liquid-gas interface during fire extinction.     

The effects of phosphorus-free inhibitors on the ignition of lycopodium dust

The minimum ignition temperature of dust suspension (MIT) and the hot surface ignition temperature of the dust layer (LIT) are essential safety parameters for the process industry. However, the knowledge of the ignition behavior when solid mixtures of flammable fuels and phosphorous-free inhibitors are considered is still scarce and further experimental and theoretical analyses are requested. In this work, the ignition temperature of phosphorous-free inhibitors (coal fly ash and calcium carbonate) mixed with lycopodium dust have been studied in terms of LIT analysis (hot plate thickness: 5 mm, 12.5 mm and 15 mm), and by the Godbert-Greenwald test for the MIT. Both coal fly ash and calcium carbonate have been tested at different concentrations and particle sizes.Results show that the effects of the inhibitor can be counter-productive when layer ignition temperature is considered even if the minimum ignition temperature of the dust suspension shows a positive effect from the safety point of view. This behavior has been analyzed in the terms of thermal conductivity and diffusivity of the mixture, by using Maxwell's equation for two-phase solid mixtures. Standard empirical correlations for the ignition temperature of solid mixtures have been also tested, showing their weakness in reproducing mixture behavior.     

Small-scale fire performance assessment of intumescent coatings on metal tubes containing ammonium nitrate. A stepping-stone towards their application as a fire safety measure on road transportation tanks?

Ammonium nitrate is used in vast amounts globally, first and foremost as a component of fertilizers and explosive formulations. This usage necessitates its transportation which, as for most hazardous materials, involves certain risks. For oxidizing materials such as ammonium nitrate, the ultimate consequence of road transportation incidents is usually considered to be fire followed by explosion. Even though the probability in general is low, substantial reduction in its risk is a great gain for public safety. Thus, identifying novel and improving current safety measures for risk reduction, is an important aspect in the field of hazardous materials. Herein, a series of experiments are reported, which demonstrate the fire protection performance of two state-of-the-art intumescent passive fire protection materials on small-scale metal test tubes containing ammonium nitrate. Albeit being initial experiments on laboratory-scale, these results provide a promising starting point for further investigations on the potential of these materials for the fire protection of ammonium nitrate when carried in metal tanks. At its best, a prominent protection of ammonium nitrate from heat exposure was observed, as the temperature was kept well below its boiling point for more than 2.5 h. Successively, it resulted in a complete recovery of the sample material. This was in large contrast to the observed results for the unprotected test tubes, which led to complete decomposition of the sample after 11 min.     

Posttreatment Tree Mortality After Forest Ecological Restoration,Arizona, United States

Pine–oak forests are of high ecological importance worldwide, but many are threatened by uncharacteristically severe wildfire. Forest restoration treatments, including the reintroduction of a surface fire regime, are intended to decrease fire hazard and emulate historic ecosystem structure and function. Restoration has recently received much management attention and short-term study, but little is known about longer-term ecosystem responses. We remeasured a replicated experimental restoration site in the southwestern United States 5 years after treatments. Basal area, tree density, and canopy cover decreased in the treated units at a faster rate than in controls. Delayed mortality, not evident right after treatment, decreased density modestly (13% in treated units and 10% in controls) but disproportionately affected large trees (“large” ponderosa pines were those with diameter at breast height [dbh] ≥37.5 cm; other species dbh ≥20 cm). In treated units, 10.9 large trees ha^–1 died, whereas 6.2 trees ha^–1 died in control units. Compared with reference conditions, the experimental blocks remained higher in pine density and, in three of the four blocks, in basal area. Pine trees grew significantly faster in treated units than in controls, enough to reach the reference level of basal area in 6 years. Although mortality of large trees is a concern, the treated units have vigorous growth and low density, indicating that they will be relatively resistant to future drought and fire events. Similar treatments may be beneficial in many areas of the United States and in related pine-oak ecosystems elsewhere.     

不同来流下火旋风的实验研究

已有的实验研究和数值模拟表明:火旋风存在一种中空燃烧的状态.本文通过燃烧风洞,对不同来流影响下的火旋风进行分析研究.通过一个置于大型燃烧风洞中的边角开有切向进风口的六边形小尺寸火旋风发生模型,应用热电偶测温和皮托管测速以及电子数据采集系统,对该模型内的温度分布数据和速度分布数据进行采集.通过燃烧风洞改变来流速度的大小,分析不同来流速度下火旋风内部的温度分布、速度分布和持续时间,研究来流速度对火旋风内部燃烧结构的影响、火旋风旋转速度的影响以及持续时间的影响.研究表明:来流改变了火旋风内部的燃烧结构,促进了中空燃烧状态的形成.中空燃烧状态有一个中心的低温区域.在中心低温区域温度最低时,火旋风持续时间最长.来流增强了火旋风的整体转动,并且加剧了火旋风的螺旋状上升.     

我国亚热带若干树种的抗火性研究

森林火灾危害森林的一大主要自然灾害,实践证明采用防火林带可以有效地控制森林火灾的发生。本文对南方的木荷、火力楠、杨梅等１１种常绿阔叶树种和杉木、马尾松两种针叶树种的叶、小枝和皮的燃烧性能及其组成成分进行了测定,结果表明,⑴各树种均以叶的抗火性能最差,阔叶树种比针叶树种的抗火性能强;⑵含水量、苯－乙醇抽取物、木质素含量和灰尘分含量是影响叶的抗火能力的主要指标。     

温升速率对某防火保护简支钢梁耐火时间的影响

在钢结构抗火研究中通常基于标准温升曲线分析钢构件的火灾响应特性,采用更接近实际火灾场景的BFD自然温升曲线,运用有限元分析软件ANSYS研究了不同火灾温升速率对某防火保护简支钢梁耐火时间的影响,并与经验公式法进行比较。结果表明:有限元分析结果与经验公式法的计算结果基本一致;不同温升速率会导致钢梁温度场变化的差异性,进而影响钢梁的耐火时间;在快速温升时,荷载大小对钢梁耐火时间的影响较大;当荷载较大时,钢梁耐火温度降低,快速温升下钢梁耐火时间较短。     

基于随机森林算法的福建省林火发生主要气象因子分析

应用"随机森林"算法,以福建省22个国家级气象站每日气象数据和2000年~2003年间林火火点卫星解译数据为基础,对影响福建省林火发生的主要气象因子进行分析,并对2004年的林火数据进行独立检验。研究结果显示,"日最高地表气温"、"日最低地表气温"、"日照时数"、"日最高气温"和"日最小相对湿度"等5个气象因子是影响林火发生的主要驱动因子,且这5个气象因子对林火发生的影响大小为:"日照时数""日最高气温""日最低地表气温""日最小相对湿度""日最高地表气温";随机森林算法的拟合结果显示:随机森林算法对福建省林火发生的预测精度为82.3%,表明随机森林算法对我国福建省林火发生的预测具有较高的预测能力,可用于基于气象因子的我国福建省林火发生的预测预报。本研究可为福建省林火的预测和决策工作提供一定的参考依据。