Poly(vinyl chloride) and its fire properties

This work provides an up‐to‐date review of the fire properties of poly(vinyl chloride) (PVC) materials, both rigid (unplasticized) and flexible (plasticized). The fire properties addressed include ignitability, ease of extinction (oxygen index), flame spread (small scale and intermediate scale), heat release, smoke obscuration, smoke toxicity, hydrogen chloride emission and decay, and performance in real‐scale fires. This comprehensive review includes a wide selection of references and tables illustrating the properties of PVC materials in comparison with those of other polymeric materials, including, in many instances, wood materials. The work puts these fire properties in perspective, showing that the heat release rate (the key fire property) of rigid PVC (and that of properly flame‐retarded flexible PVC) are among the lower values found for combustible materials. This work also shows that the smoke toxicity and smoke obscuration resulting from burning PVC materials in real‐scale fires is in the same range as those of other materials.     

Reconstruction of an arson hospital fire

An arson fire in a Swedish psychiatric detention clinic led to the death of two patients and injuries to many more. Rescue personnel were quick to go into the building on fire but had difficulties finding their way due to a very heavy smoke. The reconstruction made, indicates that a too easily ignitable mattress provided heat and radiation enough to ignite a PVC flooring material that then became the main source for fire and smoke. Analysis of soot from the fire site and measurements during the reconstruction show that the fire smoke contained large amounts of irritants that might have had an impact on the tragic outcome. In fact, comparing the toxicity of smoke gases produced during the reconstruction, based on different ‘toxicity indicators’, suggests that irritants in the fire smoke were as dangerous as or even more dangerous than the common asphyxiate type of gases present, CO and HCN. Another suggestion from the reported work is that the importance of flooring material for enclosure fire development might be overlooked. The reconstruction clearly demonstrates that the tragic fire would not have happened if the requirements for the flooring material had been the same as for the walls and ceiling materials. Copyright © 2006 John Wiley & Sons, Ltd.     

An assessment of PVC smoke

The conventional test method for evaluating the potential of a material to produce smoke in a real fire is the NBS Smoke Density Chamber. However there are major problems with this approach. These include foremost the fact that its results do not correlate with those of real fires. Furthermore, materials that melt and drip are able to achieve a favorable, but misleading, evaluation because a significant fraction of the sample escapes the burning process. Another problem is that the test takes no account of the role the rate or extent of material burning plays in controlling the smoke density in a real fire situation. The physical problems are solved by material smoke production evaluation techniques based on measurements from the Cone Calorimeter rate of heat release apparatus, which has been developed by the National Bureau of Standards. A smoke parameter has been developed, calculated from cone calorimeter measurements, which reflects the smoke hazard of a real fire. The smoke evolution characteristics for a series of rigid thermoplastic materials have been measured using the cone calorimeter and the smoke parameter concept. The results demonstrate that due to its tendency to resist ignition and to burn very slowly, PVC would produce very little smoke in a real fire situation. Of the 15 materials tested, the expected real fire smoke performance characteristics of PVC were superior to those of all other materials except one.     

Analysis of work on smoke component yields from room‐scale fire tests

Smoke Component Yields from Room‐Scale Fire Tests (NIST Technical Note TN 1453) has recently been published. This was expected to be an important work in developing concentrations and yields of toxicants that could be used for evaluating the usefulness of small scale smoke toxicity apparatuses (or fire models) for use in the prediction of the toxicity of materials and products in real fires. However, the work has a number of uncertainties that limit its potential for use as a reference. There are three major problems with this work. First, the post‐flashover concentrations of CO are too low (as recognized by the authors who recommend that this part of the data not be used). Second, the post‐flashover concentrations of the main toxicants measured (HCN and HC1) were much higher than found in most studies. Third, the precision of the data was inadequate. The consequence of the first two issues is that the work seriously overestimates the toxicological importance of gases known to have only minor effects in post‐flashover fires, such as HCN and HCl. The very low concentrations of toxicants measured at pre‐flashover conditions might have a value not discussed by the authors: an indication that pre‐flashover fires of the type conducted here do not generate extremely toxic atmospheres. Accordingly, the report does not provide reliable characteristic room scale combustion gas data that can be used for validating small‐scale furnaces. Copyright © 2005 John Wiley & Sons, Ltd.     

The effect of temperature and ventilation condition on the toxic product yields from burning polymers

A major cause of death or permanent injury in fires is inhalation of toxic gases. Moreover, every fire is unique, and the range of products, highly dependant on fire conditions, produces a wide variety of toxic and irritant species responsible for the most fire fatalities. Therefore, to fully understand each contribution to the toxicity it is necessary to quantify the decomposition products of the material under the test. Fires can be divided into a number of stages from smouldering combustion to early well‐ventilated flaming through to fully developed under‐ventilated flaming. These stages can be replicated by certain bench‐scale physical fire models using different fuel‐to‐oxygen ratios, controlled by the primary air flow, and expressed in terms of the equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio). This work presents combustion product yields generated using a small‐scale fire model. The Purser Furnace apparatus (BS7990 and ISO TS 19700) enables different fire stages to be created. Identification and quantification of combustion gases and particularly their toxic components from different fire scenarios were undertaken by continuous Fourier transform infrared spectroscopy. The relationship between type of the fire particularly the temperature and ventilation conditions and the toxic product yields for four bulk polymers, low‐density polyethylene, polystyrene (PS), Nylon 6.6 and polyvinyl chloride (PVC) is reported. For all the polymers tested, except PVC, there is a dramatic increase in the yield of products of incomplete combustion (CO and hydrocarbons) with increase in equivalence ratio, as might be expected. For PVC there is a consistently high level of products of incomplete combustion arising both from flame inhibition by HCl and oxygen depletion. There is a low sensitivity to furnace temperature over the range 650–850°C, except that at 650°C PS shows an unexpectedly high yield of CO under well‐ventilated conditions and PVC shows a slightly higher hydrocarbon yield. This demonstrates the dependence of toxic product yields on the equivalence ratio, and the lack of dependence on furnace temperature, within this range. Copyright © 2007 John Wiley & Sons, Ltd.     

聚烯烃无卤阻燃剂概况与发展方向

高分子材料用途广泛,但高分子材料大多数易燃烧,有些高分子材料燃烧时会产生大量的有害气体和烟雾,由此产生的火灾隐患成为全球关注的问题。添加有效的阻燃剂,使高分子材料具有难燃性、自熄性和消烟性,是目前阻燃技术中较普遍的方法。阻燃剂可分为含卤阻燃剂、无卤阻燃剂。目前,含卤阻燃剂仍占主导地位,但其发烟量大,燃烧时放出卤化氢气体,造成二次公害,所以高分子材料阻燃已趋向于无卤化。无卤阻燃剂有阻燃效果好、低烟、无毒等优点,因此,越来越受到重视。综述了目前常用的聚乙烯、聚丙烯塑料无卤阻燃剂的种类,相关产品及阻燃剂的发展方向。     

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.     

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.     

The influence of pressure on combustible and toxic properties of materials

Combustible and toxic properties greatly influence the application of materials in shipbuilding. These materials, especially plastics, create a serious toxic hazard during fire. Under fire conditions they decompose thermally, giving off considerable amounts of smoke and volatile toxic substances which cause a serious hazard to people overcome by fire inside a compartment.^1–3Lethal poisoning by the thermal degradation products of plastics has attracted the attention of many investigators to toxic hazards during a fire.^1,4 Underwater systems create, in particular, a serious fire hazard. Fire in a decompression chamber spreads in a different way to land fires and usually causes the death of the crew and complete destruction of equipment in the chamber. Theoretically, complete fire protection in a chamber could be achieved by the total elemination of combustible materials and their replacement by incombustible ones. However, from a practical point of view this is impossible. The general principles of materials selection used in underwater systems are defined by Det Norske Veritas.⁵ Unfortunately, these do not describe the methods of testing materials nor the criteria of materials selection. There is also a lack of information in the literature on toxic hazards under elevated pressures. This problem has been studied in detail with oxygen-enriched atmospheres in aerospace programmes,⁶ but because those studies are classified there is only fragmentary information in the literature.     

Corrosivity of smoke towards metals

Many people believe that smoke is corrosive only if it contains acid gases. This leads to associating corrosive potential of smoke from materials directly with the amount of acid gases emitted from them during combustion. In extreme cases, chemical composition (i.e. halogen content) is used as a substitute measure of corrosiveness and, therefore, of material suitability for certain applications. The reality is, however, that everything is usually heavily corroded in a fire, whatever the combustible materials involved. In the present project sets of 5 flat carbon steel coupons and 2 copper mirrors were exposed to smoke from several materials for 1 h, in a chamber at room temperature and at 100°C, and kept for 28 days at 75% relative humidity. Various surface treatments were also studied. The combustibles tested were: a PVC wire compound (PVC WR), a low acid PVC wire compound (PVC LH), a halogen free polyethylene wire compound (PE), wool, wood (Douglas fir, DFIR), polystyrene (PS), neoprene (NPR), nylon (NYL), and a blank (no sample). In order to determine corrosivity the resistance of the copper mirrors and the loss of metal from them was measured. All copper mirrors lost their electrical properties: an almost infinite resistance was measured post-exposure. The amount of copper lost was very similar for all smokes, but, in the 100°C experiments, the smoke corrosivity ranking was: All steel coupons were corroded too, at least to some extent. The amount of iron lost depended on treatment as well as on the smoke used. In particular, the highest degree of corrosion was found with coupons exposed at very high temperature, where, again, the most corrosive smoke came from nylon. Common wisdom suggests that acid gases result in corrosion of metal. The present work substantiates this fact. However, the acid gas concentration in the atmosphere does not normally correlate with the level of metal corrosion. The results of this work indicate that metal corrosion depends on factors in addition to acid gases: type of metal, temperature, humidity, length of exposure, surface treatment, and geometry. Furthermore all smokes tested are corrosive.     

The effects of brominated flame retardants on the elements of fire hazard: a re‐examination of earlier results

Addition of halogen‐containing flame retardants to reduce ignitability and flame spread is presumed to increase both the quantity of smoke produced and the toxicity of the fire effluent. In the case of brominated flame retardants (BFRs), this does not appear to be the case. This work is a re‐examination of the results of an earlier series of experiments carried out at the U.S. National Bureau of Standard (now NIST), in which product pairs were studied, one product in each pair was treated with a BFR and one was not. Comparative hazard analysis, using information not available to the original investigators, shows that, for the products under study, all three aspects of hazard — heat, smoke obscuration and fire effluent toxicity — are either reduced or unaffected by the action of the brominated agents. In particular, hydrogen bromide, a component of the fire effluent when brominated agents are present, was shown to be unimportant in the toxic hazard of full‐scale fires involving BFR‐treated products. Copyright © 1999 John Wiley & Sons, Ltd.     

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.     

Toxic gas tests in perspective

A study of the 1979 UK fire statistics and the Annual Report of the Office of Population Censuses and Surveys shows that only 1 death per 1000 is attributable to toxic gases from combustion. However, of the ‘deaths by violence’ it rises to 30 (3%). As 37% of all fires in occupied buildings were confined to the first item ignited and 53% to the area of origin it is postulated that such fires (and the consequent deaths) largely concerned substances which will burn on their own. From experience these are largely materials with limiting oxygen indices below 22 or 22–28 for restricted burning only. Those with limiting oxygen indices >28 cannot on their own sustain combustion. These considerations suggest the mode in which toxic gas tests should be conducted, i.e., horizontally or vertically and vertically only for the first two groups, respectively, and in the presence of a fire sustainer for the limiting oxygen index >28 group. Wood in the form of a wooden crib is suggested as suitable. To this end some experiments are described with PVC placed on top of a No. 5 crib (PSA). These latter show that, making the best assumption possible from the existing data, the wood contributes about 63% to the toxicity and the PVC 37%. On the large scale, other work has shown that wooden cribs alone will give lethal concentrations of carbon monoxide for significant periods. Thus difficult-to-burn substances need to evolve gases of exceptional toxicity for their contribution to be worth considering.     

Characterization of the fire environments in central offices of the telecommunications industry

Eight free burning and two sprinklered fire tests were performed with electrical cable trays and live digital switch racks in a large enclosure to simulate telecommunications central office (TCO) fires started by electrical overheating. Very‐slow‐growing (non‐flaming), slower‐growing (partially flaming) and low‐intensity‐faster‐growing (flaming) fires releasing gray‐white, gray, and black smoke, respectively, were observed in the tests. Under quiescent conditions present in the unvented enclosure fire tests for cables, very‐slow‐growing fires were detected in about 1452 s, whereas the slower‐growing fires were detected in about 222 s by commercial fire detectors. Under ventilation conditions typical of TCOs, detection times were very similar for the five types of commercial TCOs fire detectors used in the tests. The average detection times for slower‐growing fires (cable fires) and low‐intensity‐faster‐growing fires (digital switch rack fires) were 242±17% and 249±11%s respectively. The TCO procedures to reduce smoke damage from fires (on fire detection, inlet ventilation flow is turned off and exhaust flow is turned on) were found to be beneficial. The extent of smoke damage decreased significantly with an increase in the exhaust flow rate. The chloride ion mass deposition suggested that equipment recovery would be possible in the smoke environment if the cable vapor concentration could be reduced below about 3 g/m³. The metal corrosion rate was found proportional to the 0.6th power of the smoke concentration, similar to that found for the corrosion of metal surfaces exposed to aqueous solutions of HCl and HNO₃ and for acid rain with no protective layer at the surface. Sprinkler water was found to wash down the smoke deposits on the surfaces with little indication of corrosion enhancement. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

Fire effluent component yields from room‐scale fire tests

Estimation of the time available for escape (ASET) in the event of a fire is a principal component in fire hazard or risk assessment. Valid data on the yields of toxic smoke components from bench‐scale apparatus is essential to accurate ASET calculations. This paper presents a methodology for obtaining pre‐flashover and post‐flashover toxicant yields from room‐scale fire tests. The data are to be used for comparison with bench‐scale data for the same combustibles: a sofa, bookcases, and electric power cable. Each was burned in a room with a long adjacent corridor. The yields of CO₂, CO, HCl, HCN, and soot were determined. Other toxicants (NO₂, formaldehyde, and acrolein), whose concentrations were below the detection limits, were of limited importance relative to the detected toxicants. The uncertainty values were comparable to those estimated for calculations used to determine ASET and were sufficiently small to determine whether a bench‐scale apparatus is producing results that are similar to the real‐scale results here. The use of Fourier transform infrared spectroscopy was useful for obtaining toxicant concentration data; however, its operation and interpretation are not routine. The losses of CO, HCN, and HCl along the corridor were dependent on the combustible. Copyright © 2009 John Wiley & Sons, Ltd.     

Decomposition products of PVC for studies of fires

Approximately seventy-five organic materials have been detected by gas chromatography in the thermal decomposition products of PVC and are shown by mass spectrometry and retention studies to consist mainly of aromatic and aliphatic hydrocarbons. Weight-loss experiments and time-resolved chromatography indicate that these products are formed mainly during dehydrochlorination. The products are modified by the presence of oxygen but no oxygenated organic species have been detected. Experiments to specifically monitor the production of phosgene from the decomposition of both a rigid PVC sheet and a PVC polymer in air are recorded. Phosgene has not been detected and direct seeding techniques have been used to investigate the detection limits of this material. PVC is known to release the toxic gases, carbon monoxide and hydrogen chloride, when involved in fires. It is shown that the minor products, including phosgene, make little or no contribution to the overall toxicity of the decomposition products.     

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。     

The fire performance of PVC

The role of PVC in fires is currently a controversial topic because of the many negative comments made about PVC on the occurrence of any major fire disaster. Critics also use many small-scale smoke and toxic gas tests to define the role of PVC in these fires. The purposes of this paper are (1) to summarize the current technical knowledge of real fire behavior, (2) use this understanding to interpret available data for PVC in large- and small-scale fire tests, and (3) help bring a sense of technical realism to the issues involved.