Investigation of smoke gases and temperatures during car fire – large‐scale and small‐scale tests and numerical investigations

The hazards for passengers during vehicle fires result from the increasing temperature and the emitted smoke gases. A fire was set on a car to investigate the development of temperature and of gaseous fire products in the passenger compartment. The study was based on a full‐scale test with a reconstructed scene of a serious car fire. The aim of this work was to identify the conditions for self‐rescuing of passengers during a car fire. A dummy, equipped with several thermocouples, was placed on the driver's seat. Also, the smoke gases were continuously collected through a removable probe sensor corresponding to the nose of the dummy in the passenger compartment and analyzed using Fourier transform infrared spectroscopy. Additionally, several car components were investigated in the smoke density chamber (smoke emission and smoke gas composition). It was found that the toxic gases already reached hazardous levels by 5 min, while the temperatures at the dummy were at that time less than 80 °C. The toxicity of smoke gases was assessed using the fractional effective dose concept. The various experimentally parameters (temperature and smoke gas composition) were implemented into numerical simulations with fire dynamics simulator. Both the experimental data and the numerical simulations are presented and discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

CFD modeling approach of smoke toxicity and opacity for flaming and non‐flaming combustion processes

Current engineer's methods of fire safety design include various approaches to calculate the fire propagation and smoke spread in buildings by means of computational fluid dynamics (CFD). Because of the increased computational capacity, CFD is commonly used for prediction of time‐dependent safety parameters such as critical temperature, smoke layer height, rescue times, distributions of chemical products, and smoke toxicity and visibility. The analysis of smoke components with CFD is particularly complex, because the composition of the fire gases and also the smoke quantities depends on material properties and also on ambient and burning conditions. Oxygen concentrations and the temperature distribution in the compartment affect smoke production and smoke gas toxicity qualitatively and quantitatively. For safety designs, it can be necessary to take these influences into account. Current smoke models in CFD often use a constant smoke yield that does not vary with different fire conditions. If smoke gas toxicity is considered, a simple approach with the focus on carbon monoxide is often used. On the basis of a large set of experimental data, a numerical smoke model has been developed. The developed numerical smoke model includes optical properties, production, and toxic potential of smoke under different conditions. For the setup of the numerical model, experimental data were used for calculation of chemical components and evaluation of smoke toxicity under different combustion conditions. Therefore, averaged reaction equations were developed from experimental measurements and implemented in ANSYS CFX 14.0. Copyright © 2015 John Wiley & Sons, Ltd.     

Toxic gas and smoke measurement with the British Fire Propagation test. I: Test conditions

No standard method has been developed for measureing the evolution of specific toxic gases from building lings when involved in fire. The British Fire Propagation test (BS 476 Part 6) operated in an instrumented room has been proposed for this purpose previously but has not found general acceptance. It is considered further in this report, which investigates the movement and measurement of smoke and specific fire gases under different conditions of room stirring and the effect of the latter on fire propagation indexes. Stiring has been found to have no statistically significant effect on fire propagation indexes provided that the effects of this on calibration of the apparatus are taken into account. Stirring also had little effect upon smoke production per se. Under unstire conditions smoke and toxic gases stratify in the same layer early in the test, and measurement of their production at any single room location will be subject to the location, the way the room influences stratification and how the room is instrumentee, as well as by the prpduct performance. Under stirred room conditions smoke and toxic gases are evenly distributed and product performance can be assessed more simply from concurrent measurements of fire, smoke and toxic gas parameters. The latter procedure is proposed for obtaining relative data on building linings and for examination in further studies for correlation to room and corridor burns.     

Theory of fire and fire processes

There are two major fire processes, an understanding of which is essential for effective fire safety design: (1) the conditions under which a combustible material may become involved in flaming combustion, and (2) the rate at which such a material, once involved, will provide an output of heat, smoke, toxic gases, etc., which can endanger people and property. The first process may be regarded as covering both ignition and spread of fire on materials; its complement is the way in which fire may become extinguished. It is necessary for such processes to bring in a characteristic of the basic combustion reaction which, directly or indirectly, expresses the reactivity of the combustion process. Thus pilot ignition is usually associated with an approximate surface fuel temperature. More basically, it is associated with a critical flow rate of volatiles and a critical heat loss from the flame, the latter being influenced by ambient oxygen and temperatures conditions as well as heat lost and gained by the fuel itself. The most important factor governing the production of dangerous product is the rate at which volatiles first (fuel controlled fires) and later air (air controlled fires) are fed into the flames. The reactivity is of less importance, although it may be one of the factors which control combustion efficiency. In general, the more efficient is the combustion the more heat is produced, but the less smoke and toxic gases are produced. Some of the main advances in the above areas are reviewed in this paper.     

Update on smoke toxicity of vinyl compounds

All organic materials burn and give off toxic products. These always include water, carbon dioxide, and the single gas causing the greatest hazard in fires—carbon monoxide (CO). The intrinsic toxicity of the smoke of all combustible materials, including PVC, is very similar in terms of lethality, with very few exceptions. Toxicity of vinyl compounds is due to two major gases: CO and hydrogen chloride (HCI). Since natural combustible materials are not chlorinated, speculation has arisen about the toxicity of HCl and of PVC smoke. Recent studies have shown that it takes similar doses of HCl and CO to kill rats. Furthermore, rats and baboons will tolerate the same levels of HCl. However, mice are much more sensitive than either rats or baboons towards HCl. Baboons are a very good model for humans; therefore, mice will be killed by exposure to much lower HCl levels than those required to kill humans. HCl concentrations in real fires are quite low: HCl decays rapidly by reacting with wall materials such as gypsum, cement, or ceiling tile. It does not, however, react rapidly with plastic or glass walls, which is where toxicity tests are carried out. Therefore PVC smoke is less hazardous in reality than it appears to be from toxicity test results. Since most products have similar intrinsic toxicities, as regards lethality, the real toxicity in a fire is a consequence of the rate of generation of gases. PVC is a difficult polymer to ignite and burns very slowly, so that it will give off less toxic products per unit time than many other common materials and cause lower fire hazard.     

Smoke gas analysis by Fourier transform infrared spectroscopy – summary of the SAFIR project results

The determination of toxic components from fire gases is difficult because the environment is hot, reactions are often temperature dependent, and a lot of soot may be produced. Due to the different properties of the gas components, a different time‐consuming procedure for each species has traditionally been used. The use of FTIR (Fourier transform infrared) spectrometers as a continuous monitoring technique overcomes many of the problems in smoke gas analyses. FTIR offers an opportunity to set up a calibration and prediction method for each gas showing a characteristic spectral band in the infrared region of the spectrum. The objective of the SAFIR project was to further develop the FTIR gas analysis of smoke gases to be an applicable and reliable method for the determination of toxic components in combustion gases related to fire test conditions. The optimum probe design, filter parameters and the most suitable sampling lines in terms of flow rate, diameter, construction material and operating temperature have been specified. In the large scale, special concern was given to the probe design and the effects of the probe location as well as practical considerations of the sampling line length. Quantitative calibration and prediction methods have been constructed for different components present in smoke gases. Recommendations on how to deal with interferents, non‐linearities and outliers have been provided and a verification method for the spectrometer for unexpected variations and for the different models have been described. FTIR measurement procedures in different fire test scenarios have been studied using the recommendations of this project for measurement techniques and analysis and an interlaboratory trial of the FTIR technique in smoke gas analysis was carried out to define the repeatability and reproducibility of the method in connection with a small scale fire test method, the cone calorimeter. Copyright © 2000 John Wiley & Sons Ltd.     

Quantification of threat from a rapidly growing fire in terms of relative material properties

Equations have been developed which give the time available for escape or rescue, i.e., the time interval between detection and blockage of the escape route by smoke, heat or toxic gases. Alternative assumptions are explored concerning exponential vs power law fire growth and an extended fire plume vs uniform filing of the building. The equations are developed in such a form that the threat variable by which the fire is detected is not necessarily the same threat variable which first blocks the escape route. A number of interesting results have been obtained, and numerical values of key parameters measured in various test fires at Factory Mutual Research are tabulated. It is shown that for many polymeric fuels smoke will block the escape route well before temperature or toxicity becomes excessive. In such cases, if the fire, assumed to be growing exponentially, is detected by its smoke, the detector being located in the escape route, then the escape time, surprisingly, is independent of the smokiness of the material as well as the size and shape of the building. It is determined only by the growth rate constant (doubling time) of the fire and the sensitivity of the detector.     

Detailed determination of smoke gas contents using a small‐scale controlled equivalence ratio tube furnace method

A series of tests including seven different materials and products have been conducted using a controlled equivalence ratio tube furnace test method. The main objective of the tests was to determine yields of fire‐generated products at defined combustion conditions. The tube furnace test method was set up and run in close agreement with that described in BS 7990:2003. At the time of experimental work the new tube furnace method was in the process of becoming an international standard. It was thus of interest to make an assessment of the capability of the method for determining production yields of important toxic fire products from different types of materials and products. The test series included solid wood, flexible polyurethane (PUR), fire‐retarded rigid PUR, a polyvinyl chloride (PVC) carpet, a high‐performance data cable with fluorine‐containing polymer matrix, a PVC‐based cable sheathing material and fire‐retarded polyethylene cable insulation material. Duplicate tests were generally conducted at both well‐ventilated and vitiated combustion conditions with these materials. The smoke gases produced from the combustion were quantified for inorganic gases by FTIR technique in all tests. A more detailed analysis of the smoke gases was conducted for some of the materials. This extended analysis contained a detailed assessment of organic compounds including, e.g. volatile organic compounds, isocyanates, aldehydes and polycyclic aromatic hydrocarbons. The analysis further included measurement of the size distribution of fire‐generated particles for some of the materials. The quantification of toxic inorganic gases produced by combustion at both well‐ventilated and vitiated conditions was successful regarding repeatability and stability. Typical yields for the two fire stages investigated were determined for a wide range of materials and products. The detailed analysis of organic compounds further corroborated that the new tube furnace method can replicate defined combustion conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Feasibility study to demonstrate the potential of smoke hoods in simulated aircraft fire atmospheres: Development of the fire model

The subject of this paper is the development of a fire model producing smoke similar to that which could be anticipated from a burning passenger aircraft in the period before flashover. The simulated aircraft fire smoke was used to test filter and oxygen-donating smoke hoods as part of the Accident Investigation Branch research programme initiated after the Boeing 737 fire at Manchester in 1985. A relatively simple approach was adopted in which materials used in passenger aircrafts cabins were burned in an enclosed room. The smoke hood exposure tests were then carried out in the same room. The fire model permitted the smoke hoods to be tested for 5-min periods with an atmosphere approximating to that required and for longer periods with atmospheres with reduced concentrations of the more polar gases. Analytical procedures enabled both challenge atmospheres and filter penetration to be assessed. The evaluation of smoke hoods by Rapra Technology and British Coal demonstrated that filter smoke hoods were capable of providing protection (providing there was sufficient oxygen to sustain life), that carbon dioxide did not cause debilitation and that the heat produced by the oxidation of carbon monoxide was dissipated. Oxygen-donating systems were also capable of providing protection for the duration of their oxygen supply but it was necessary to prevent the build-up of carbon dioxide. Other important factors, such as the effectiveness of smoke hood to head seals and the effect of hood donning on aircraft evacuation times, have not been examined in this paper.     

Towards regulating toxicity of materials in building

A method is presented for evaluating the toxic hazard resulting from the thermal decomposition of materials used in buildings or other closed structures. It was developed in conjunction with the current revision of Israel Standards pertaining to the behavior in fire of building materials. The method is based on the measurement and evaluation of those gases recognized as hazardous in fire situations. A ‘toxicity ratio’ of the materials is defined in terms of the sum of concentration ratios of all toxic gases monitored to the corresponding lethal threshold limit concentration levels. The ‘toxicity index’, a material property, relates the toxicity ration to the material quantity and the plenum volume. The toxicity index is found by experiment for specimens heated to their smoldering and flaming temperatures in a closed system. Fire hazard levels due to toxic gases emitted from different materials can then be compared using the toxicity ratio computed for the specified situation. The proposed method is compatible with Israel Standards IS 921, where allowable levels for buildings and compartments are defined.     

高分子材料火灾烟气的危害及控制

介绍了高分子材料火灾烟气的产生及主要有害成分的组成。烟气对人员逃生、火灾救援产生的影响；烟气对生态环境造成的危害；根据高分子材料燃烧机理，提出了减少烟气毒性和环境危害的措施。     

Dangers relating to fires in carbon‐fibre based composite material

Inhalable carbon fibres have been suspected to pose similar threats to human health as asbestos fibres. It is well‐known that fibres having a diameter of less than 3 µm might be inhaled and transported deep into the human respiratory system. Some composite materials use carbon fibres as structural reinforcement. These fibres do not pose any risks as such as they are firmly connected to the laminate and surrounded by a polymer matrix. Also, these fibres typically have diameters >6 µm and thus, are not inhalable. However, if the material is exposed to a fire, the carbon material might be oxidized and fractionated and thereby, inhalable fibres might be generated into the fire smoke. The capability of carbon fibre‐based composite material to produce dangerous inhalable fibres from different combustion scenarios has been investigated. It was found that the risk of fires generating inhalable carbon fibres is related to the surface temperature, the oxygen level and the airflow field close to the material surface. The temperatures necessary for oxidation of the carbon fibre is so high that it is possible that only a flashover situation will pose any real danger. Other possible danger scenarios are highly intense fires (e.g. a liquid fuel fire), or situations where structural damage is part of the fire scenario. Copyright © 2005 John Wiley & Sons, Ltd.     

浅述几类化学危险品的基本特性、火灾预防措施及灭火方法

化学危险品是具有爆炸、易燃、毒害、感染、腐蚀、放射性等危险特性,在运输、储存、生产、经营、使用和处置中,容易造成人身伤亡、财产损毁或环境污染而需要特别防护的物品。文章介绍了易燃固体、自燃物品及遇水放出易燃气体的物质、易燃液体、危险气体、爆炸品、毒性物质和感染性物质、氧化性物质和有机过氧化物六类化学危险品的基本特性,说明了其火灾预防措施,并概述了它们在发生灾害事故时的处置措施或灭火方法。     

Combustion products of polymeric materials. 1—Test chamber CAB 4.5

A test chamber for performing complete investigation of the dangerous effects of thermal degradation products of polymeric materials has been designed. The tow-chamber system with separated combustion chamber and smoke chamber has a steep temperature gradient between both chambers and enables continuous analysis of combustion products of the tested polymeric material for carbon monoxide and carbon dioxide to be performed, to monitor the oxygen content in the chamber during testing and to perform tests of biological toxicity on mice as test animals. The function of the test chamber was verified on combustion of polyethylene, polypropylene, polystyrene and polyamide samples.     

Ignition,combustion, toxicity,and fire retardancy of polyurethane foams: A comprehensive review

This review provides insight into the ignition, combustion, smoke, toxicity, and fire‐retardant performance of flexible and rigid polyurethane foams. This review also covers various additive and reactive fire‐retardant approaches adopted to render polyurethane foams fire‐retardant. Literature sources are mostly technical publications, patents, and books published since 1961. It has been found by different workers that polyurethane foams are easily ignitable and highly flammable, support combustion, and burn quite rapidly. They are therefore required to be fire‐retardant for different applications. Polyurethane foams during combustion produce a large quantity of vision‐obscuring smoke. The toxicity of the combustion products is much higher than that of many other manmade polymers because of the high concentrations of hydrogen cyanide and carbon monoxide. Polyurethane foams have been rendered fire‐retardant by the incorporation of phosphorus‐containing compounds, halogen‐containing compounds, nitrogen‐containing additives, silicone‐containing products, and miscellaneous organic and inorganic additives. Some heat‐resistant groups such as carbodiimide‐, isocyanurate‐, and nitrogen‐containing heterocycles formed with polyurethane foams also render urethane foams fire‐retardant. Fire‐retardant additives reduce the flammability, smoke level, and toxicity of polyurethane foams with some degradation in other characteristics. It can be concluded that despite many significant attempts, no commercial solution to the fire retardancy of polyurethane foams without some loss of physical and mechanical properties is available. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Smoke and fire assessment with the fire propagation test

Assesing the total potential fire hazard of modern interior surfacing of buildings requires a method which includes determination of smoke toxicity concurrently with fire and smoke production parameters. The Fire Propagation Box Test (British Standards Institution BS 476, Part 6) is a promising contender. It has been examined in the flaming mode as a method for evaluating smoke production concurrently with fire propagation indices for a range of surfacings, rather than resorting to a separate procedure by using fans with the same apparatus, as described in the former British Standards Institution Draft for relation to rate of burning the concurrent procedure is shown to be the more valied method.     

Fire conditions for smoke toxicity measurement

This paper identifies those fire conditions most often present when smoke toxicity is the cause of death. It begins with a review of the evidence that smoke-inhalation deaths are in the majority in fire fatalities in the United States. Next, there is an analysis of the evidence from the national fire experience showing the connection between post-flashover fires and smoke-inhalation deaths. Third is a presentation of real-scale fire test results demonstrating that post-flashover conditions are necessary to produce enough smoke to cause smoke-inhalation deaths in the cases where they actually occur. The fourth component is a sampling of results from computer simulations of fires, affirming and broadening the results from the fire tests. It is concluded that smoke-inhalation deaths occur predominantly after fires have progressed beyond flashover. This conclusion then provides a focus for smoke toxicity measurement in particular and fire hazard mitigation in general.     

常用建筑材料的烟气毒性浅析

建筑火灾中产生的有毒烟气是造成人员伤亡的主要原因,随着我国经济的发展,建筑的数量越来越多,更有大量的可燃以及阻燃建筑材料被应用,这就大大增加了发生烟气毒性伤害的几率。开展对火灾烟气毒性的研究具有重要的意义。本文介绍了几大类建筑材料产烟毒性的测定和比较,阐述了烟气毒性定量评价方法,并介绍了其在建筑性能化评估中的应用。     

Assessing smoke toxicity of burning combustibles by four expressions for fractional effective dose

Toxicity of smoke generated in a fire is difficult to measure accurately. That is because gas sensors for measuring rapidly varying concentrations of toxic gases are not yet developed. Simple expressions are searched for quick measurement in assessing smoke toxicity practically. Four equations on calculating fractional effective dose (FED) related to toxic effluents were reported in the literature, each based on different assumptions. FED value was proposed to be calculated based on peak carbon monoxide concentration and peak carbon dioxide concentration, and transient carbon monoxide, carbon dioxide, and oxygen concentrations. The four values were compared in this article using literature data on toxic gases from different materials measured by (i) cone calorimeter; (ii) full-scale burning tests; and (iii) tunnel full-scale tests. Measured carbon monoxide, carbon dioxide, and oxygen concentrations by standard equipment of oxygen consumption calorimeters were used to calculate the four FED values. It is found that the values of FED based on peak carbon monoxide and carbon dioxide concentrations (denoted as FED₂) are similar to the average values of FED calculated from the updated equation in the literature using the oxygen consumption calorimeters. Putting the values of FED₂ in fire safety design guides is then recommended.     

Comparison of the smoke toxicity of four vinyl wire and cable compounds using different test methods

Four vinyl wire and cable materials were tested using five smoke toxic potency test methods: the NBS cup furnace test (in its flaming and non-flaming modes), the NIST radiant test, the NIBS IT₅₀ test (also using the radiant apparatus) and the UPITT test. One of the materials is a standard poly(vinyl chloride) (PVC) flexible wire and cable material, used commercially for wire insulation. The three other materials tested represent a new family of vinyl thermoplastic elastomer alloys, which are advanced materials with good fire performance, particularly in terms of heat release and smoke obscuration. It was found that the smokes from all four materials are similar in terms of their toxic potencies, and that they are all within the ‘common’ range of toxic potency found. In particular, the toxic potencies of the smoke from the new vinyl thermoplastic elastomer alloys are not significantly different from those of other traditional vinyl wire and cable compounds. The results of the tests were also interpreted in terms of the toxicities and concentrations of the individual gases emitted. The fractional effective dose of the toxicants analysed was sufficient to account for the toxicity of the smoke for the NBS cup furnace and the NISt radiant test. It was not able to account for the toxicity found in the UPITT test. The adequacy of the test protocols themselves was also investigated. It was found that the UPITT and the NIBS IT₅₀ method are inadequate for measurement of smoke toxicity. It was also found that the NIST radiant test protocol is the one most likely to lead to the smallest amount of future testing.