建筑火灾烟气流动的分析及控制

日本神户大学研究院松下敬幸先生,从事建筑火灾烟气流动研究多年,成果颇丰,荣获2005年度日本火灾学会奖。现将他的研究成果简介于下。1创立火灾烟气流动计算的SMK体系烟气流动计算的目的之一,是研究火灾时人员疏散安全问题。影响烟气流动的因素有:人群疏散时开门、闭门;最终避难场所在地面上,所以逃生路线都是通向地面的;土建设计时,房间的配置和分隔常有很大变化,门窗等开口部分的布置方式也有较大区别。因此,烟气流动计算体系,应当是能够对应于建筑内人员疏散流动,且与许多房间及空间相关联的计算体系。这就要求经常获取及积累与门窗等…     

建筑火灾过程中烟气与热排放作用分析

分析了建筑火灾过程中烟气与热排放的目的，我国相关技术规范与欧共体及德国标准相比的不足之处，在此基础上系统地介绍了烟气与热排放的工程方法及烟气与热排放的计算方法，并通过工程实例分析了烟气与热排放的作用效果。     

封闭空间火灾中燃料烟尘对墙体所受热通量的影响

尽管在封闭空间内已经做过很多关于气体温度和燃烧率的研究,但目前仍然缺乏封闭空间内墙体上热通量及其分布方面的信息。该热通量数据是确定墙体材料特别是玻璃的热反应及性能的必要输入参数。试验用封闭空间墙体上的热通量是通过多块薄钢片(25.4mm×25.4mm×3mm)以及钢片周围隔热材料的温度推算出来的。另外,笔者还测量了热流计附近墙体的质量损失率和温度。试验用封闭空间是ISO标准墙脚火试验的1/3,有六个开口,燃料为甲醇、IMS(工业用甲基化酒精)以及甲苯,装在大小不同的三个方形油盘里,油盘放置在封闭空间的内外拐角处。在选择燃料方面,笔者的依据是燃料燃烧产生的烟尘应越来越浓。试验发现,与以前对地板的研究结果有所不同的是,墙体上的热通量不仅仅取决于烟气温度,还取决于热释放速率的强弱以及燃料所产生的烟尘的多少。另外,对甲醇、IMS以及甲苯所产生的热通量的比较发现,对流热可以与辐射热通量(热烟气流以及封闭墙体造成)以及来自烟羽流的辐射热通量分开。     

Modeling the movement of smoke and the effect of ventilation systems in mine shaft fires

Physical principles governing mine ventilation systems and state of the art ventilation modeling are initially outlined. Several computer programs for modeling the mine ventilation-mine fire interaction, which were developed during the last decade, are then described. An older program considers fires and ventilation systems as going through a sequence of steady state conditions. Airflow rates, pressure losses, temperatures, fume and methane concentrations can be determined. Newer programs allow transient state fume concentration calculations under the assumption of constant airflow rates as well as the determination of fume exposures of escaping miners. Recent work attempts the complete transient state simulation of fires and all ventilation properties.     

Control of smoke in building fires

In the August issue, the author discussed the movement of smoke in buildings. In this, a companion article, he examines an approach to controlling the movement of smoke to permit safe evacuation of a building and to lessen its hampering effect on fire fighting operations.     

A numerical study on smoke movement in longitudinal ventilation tunnel fires for different aspect ratio

In this study, numerical simulation was carried out to analyze the effect of the aspect ratio on smoke movement in tunnel fires using FDS 3.0. Temperature distribution under the ceiling showed a relatively good agreement with experimental results within 10 °C. It confirmed the possibility of application of FDS code to tunnel fires. Results from varying of the aspect ratio showed good agreement with experimental data. Temperature near the fire source decreased with the increase of the aspect ratio. But, the rate of the temperature decrease was reduced by the decrease of the heat loss in the spanwise direction. Clear height of the simulation by the analysis of the velocity distribution was about 3% higher than that of the experimental result. Numerical results predicted the back-layering distance and the critical velocity reasonably.     

Estimation of the smoke produced in fires

Some of the major difficulties that confront the estimation of smoke that may be produced at fires are considered. They include the confusion over the units in which smoke is expressed, reliability of laboratory test methods for smoke production developed so far, and the factors which may cause a difference between laboratory tests on the one hand and fire tests in general, and fire ground conditions on the other. Information on some of the latter factors is reported in the experimental results on the smoke produced by samples of materials of different height, burning freely, both singly and as combinations of two materials comprising the sides of a small, square chimney. It was found that within the range of heights of chimney of 3.2 – 15 cm the smoke potential of materials, D_o (smoke produced per unit weight of volatiles), reduced as the height increased by a factor of 1.5 – 2. In general, also, the contribution of different materials was additive unless one of them did not burn well by itself, in which case less smoke was produced than expected.In addition, a number of approximate working formulae have been developed to estimate D_o of materials burned in fire tests, from measurements of smokiness, D_L, obtained in the test, together with other data, such as gas analyses or temperature, that may be available. D_o is expressed in units of ob m³/g, which is based on a new unit for smokiness, the obscura (ob), used to express D_L. On the whole, values of D_o obtained in this way did not differ radically from values obtained under flaming conditions using bench tests, but there is evidence that under ventilation-controlled conditions with vertical vents, substantially higher values of D_o may be obtained than under fuel-controlled conditions. From information on D_o thus obtained, combined with information on D_o available from bench tests, a tentative list of values of D_o is given, for different materials burning under different conditions, which may be used as a first step towards predicting smoke output and smokiness in fire situations.     

Controlling the spread of smoke in fires

In a building fire it is often the spread of smoke into crucial areas that presents the greatest obstacle to escape. The problem is therefore to control this process, especially in ‘compartmented’, multi-occupation buildings. The principles are discussed here and related to the smoke-control systems currently available throughout the world.     

Control of smoke flow in tunnel fires

This paper concerns the specification of the longitudinal ventilation necessary to prevent upstream movement of combustion products in a tunnel fire. Experiments carried out in a model tunnel have revealed significant limitations on the utility of existing empirical expressions for the critical velocity. Simple formulae with a wider range of applicability are presented. The method of scaling model results has been tested by comparison with large-scale test data. The effects of changes in the shape, size and location of the fire on the critical velocity have been investigated.     

Fire spread and smoke control in high-rise fires

Based on experience gained in the Henry Grady Hotel smoke and fire tests, the authors have formulated some recommendations for the improvement of future full-scale fire experimentation.     

室内火灾旋转火焰理论分析与实验研究

根据涡量传输和火灾动力学等理论,分析室内火灾旋转火焰的形成机理,导出室内火灾产生旋转火焰的控制因素表达式。旋转火焰的产生需要足够的密度梯度、压力梯度和斜压效应。利用小规模室内火灾实验,研究室内火灾旋转火焰的基本特征,比较旋转与非旋转火焰火灾的基本参数。与非旋转火焰的室内火灾比较,旋转火焰室内火灾热烟气层温度、升温速率、燃烧速率、地板所受辐射热通量等的均值与峰值均有显著提高,且峰值出现较早。结合理论分析与实验研究结果,得到了室内火灾发生旋转火焰的条件判据。     

建筑火灾烟气迁移特性研究及排烟设计

在火灾烟气迁移和机械加压补风的理论研究基础上,基于FDS火灾模拟软件的大涡模拟（LES）及Smagorinsky亚格子尺度模型对某大学宿舍楼进行实体建模。危害性气体CO在水平方向上的体积分数演变非常相近,火源处产生的危害性气体成分能够沿着水平方向传播到远距离处而自身体积分数的变化很小,CO的体积分数峰值随高度呈现明显的阶梯变化。数值模拟结果证明,火灾中大量的人员都死于远距离处的主要原因可能是吸入了大量迎面而来的（而不是身后面赶上的）烟气中危害性气体CO,由此对建筑防火结构设计中针对高层建筑火灾烟气迁移问题提出了改进意见。     

Smoke movement in fires and its control

The problems caused by the movement of smoke in building fires have received particular attention in Japan, where large scale field tests have supplemented laboratory studies, in collaborative projects by the Building Research Institute in Tokyo, Kyoto University, the Science University of Tokyo and the Tokyo Fire Department. The design implications are discussed in this paper by one of the leading experts on the subject at the Tokyo Building Research Institute.     

Estimation of smoke arrival time in tunnel fires

The estimation of smoke arrival time in tunnel fires is helpful to comprehensive fire risk assessment and effective fire evacuation, while few studies focused on this topic. A model to estimate the arrival time of fire smoke in tunnels is derived based on the smoke temperature distribution along the tunnel ceiling. The predictions from the model are compared to experimental data from one past study, which shows good agreements. The influencing factors of the smoke arrival time are studied based on the model. Results show that the Stanton number is the main influencing factor. The smoke arrival time increases with the increase of the Stanton number.     

Estimating smoke production during building fires

In the absence of specific analytical methods for measuring the hazards of fire gases, there is a trend toward the use of smoke production as a partial measure of this hazard. It is indicated that prediction of smoke concentrations and thus photometric properties during actual fires requires many important and rather critical assumptions. Note: This paper is a contribution of the National Bureau of Standards and is not subject to copyright.     

Measurement of the smoke layer interface in fires

In the normal case, as we all know, when there is a fire, smoke will arise along with the fire. The height of the smoke layer interface is an important parameter to assess a fire hazard. A smoke generator was used in a hot smoke test. The test verified the feasibility of two methods of measuring the smoke layer interface: ocular estimate and thermocouple measurement. The findings show that the ocular estimate is less accurate because subjective factors of the observer lead to changes of the data while the thermocouple measurement is more accurate. It has a delay in measurement, so revision of the delay should be taken into account and the two methods can be complementary.     

Energy distribution analysis in full-scale open floor plan enclosure fires

Within a fast evolving built environment, understanding fire behaviour and the thermal exposure upon structural elements and systems is key for the continued provision of fire safe designs and solutions. Concepts of fire behaviour derived from research in enclosure fires has traditionally had a significant impact in general building design. At present, open floor plan enclosures are increasingly common – building design has drastically drifted away from traditional compartmentalisation. Nevertheless, the understanding of fire behaviour in open floor plan enclosures has not developed concurrently. The compartment fire framework, first conceived for under-ventilated fires in cubic compartments, has remained as standard practice. Although energy conservation within the enclosure was the basis for the current compartment fire framework that defines under-ventilated enclosure fires, little effort has been carried towards understanding the distribution of energy in design frameworks conceived for open floor plan enclosure fires. The work presented herein describes an analysis of the energy distribution established within an experimental full-scale open floor plan enclosure subjected to different fire modes and ventilation conditions. The results aim to enable the designer to estimate the fraction of the total energy released during a fire noteworthy to structural performance.     

室内火灾过程的傅里叶分析及其应用

根据小规模室内火灾试验的结果,利用傅里叶分析的方法,研究室内火灾过程;初步探讨有关研究结果在实际消防工作中的应用。结果表明:室内火灾过程的傅里叶分析为室内火灾过程的研究开辟了新的途径,其研究结果可用于预测室内火灾热烟气层温度变化的历程和轰燃发生的可能性。     

Statistical characterization of the time to reach peak heat release rate for nuclear power plant electrical enclosure fires

Since publication of NUREG/CR-6850 (EPRI 1011989), EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities in 2005, phenomenological modeling of fire growth to peak heat release rate (HRR) for electrical enclosure fires in nuclear power plant probabilistic risk assessment (PRA) has typically assumed an average 12-min rise time [1]. One previous analysis using the data from NUREG/CR-6850 from which this estimate derived indicated this could be represented by a gamma distribution with alpha (shape) and beta (scale) parameters of 8.66 and 1.31, respectively [2]. Completion of the test program by the US Nuclear Regulatory Commission (USNRC) for electrical enclosure heat release rates, documented in NUREG/CR-7197, Heat Release Rates of Electrical Enclosure Fires (HELEN-FIRE) in 2016, has provided substantially more data from which to characterize this growth time to peak HRR [3]. From these, the author develops probabilistic distributions that enhance the original NUREG/CR-6850 results for both qualified and unqualified cables.² The mean times to peak HRR are 13.3 and 10.1 min, respectively, with a mean of 12.4 min when all data are combined, confirming that the original NUREG/CR-6850 estimate of 12 min was quite reasonable.Via statistical-probabilistic analysis, the author shows that the time to peak HRR for qualified and unqualified cables can again be well represented by gamma distributions with alpha and beta parameters of 1.88 and 7.07, and 3.86 and 2.62, respectively. Working with the gamma distribution for All cables given the two cable types, the author performs simulations demonstrating that non-suppression probabilities, on average, are 30% and 10% higher than the use of a 12-min point estimate when the fire is assumed to be detected at its start and halfway between its start and the time it reaches its peak, respectively. This suggests that adopting a probabilistic approach enables more realistic modeling of this particular fire phenomenon (growth time).