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.     

Isocyanates,aminoisocyanates and amines from fires—a screening of common materials found in buildings

Isocyanates, aminoisocyanates and amines were quantified from the combustion of 24 different materials or products typically found in buildings. Small‐scale combustion experiments were conducted in the cone calorimeter, where generally well‐ventilated combustion conditions are attained. Measurements were further made in two different full‐scale experiments. Isocyanates and amino‐compounds were sampled using an impinger‐filter sampling system with a reagent solution of di‐n‐butylamine in toluene. Filter and impinger solution were analysed separately using LC‐MS technique. Further the particulate distribution in the smoke gases was determined by impactor technique, and selected gaseous compounds quantified by FTIR. It was found in the small‐scale that isocyanates were produced from the majority of the materials tested. The highest concentration was found for glass wool insulation, and further high concentrations were found for PUR products, particleboard, nitrile rubber and melamine. Lower concentrations were found for wood and cable‐products. Amino‐isocyanates and amines were generally found from PUR products only. The distribution of isocyanates between the particulate‐ and fluid phases varied for the different materials and a tendency to enrichment of particles was seen for some of the materials. Further, when comparing the potential health hazard between isocyanates and other major fire gases (based on NIOSH IDLH‐values) it was found that isocyanates in several cases represented the greatest hazard. Copyright © 2003 John Wiley & Sons, Ltd.     

Cable tray fire tests with halogenated electric cables in a confined and mechanically ventilated facility

Cable fires are one of the main fire hazards present in nuclear power plants (NPPs). Therefore, as part of the Organisation for Economic Co‐operation and Development (OECD) PRISME‐2 project, cable tray fire tests were performed both in open atmosphere conditions and in a confined and mechanically ventilated facility, called DIVA. These tests aim at showing the effects of a confined and ventilated environment on fire characteristics and consequences. This study deals with five fire tests, which used halogenated (poly [vinyl chloride] or PVC) cable types. Two tests were carried out in open atmosphere and three tests in the DIVA facility. The latter used a ventilation renewal rate (VRR) of either 4 or 15 h^?1. The confined and ventilated conditions reduced the mass loss rate and heat release rate than did those obtained in open atmosphere. Furthermore, the three confined tests produced unburnt gases, which ignited in the fire room. Two explosions were highlighted for the tests that used a VRR of 4 h^?1. These explosions indeed led to fast flame propagations over the entire upper part of the fire room and steep overpressures of almost 150 hPa. The low‐qualified PVC cables and the ventilation set‐up used in this study strongly contributed to the occurrence of these explosions.     

Numerical investigation of tube furnace toxicity measurement method (ISO 19700)

ISO TS 19700 describes a test method for the generation of fire effluent and the identification and measurement of its constituent combustion products. The method has been previously accepted as a British Standard (BS 7990:2003) and as an IEC Standard (IEC 60695‐7‐50), which involves the decomposition of materials or products under various decomposing conditions occurring in different types and stages of real fires. It uses a moving test specimen and a tube furnace at different temperatures and air flow rates as the fire model. Simulations of flow and combustion conditions inside the tube (Purser) furnace were carried out and validated with the measurements. The objective of the present study is to demonstrate the validity of using computational fluid dynamics (CFD)‐based fire field modelling techniques to predict the fire environment inside the tube furnace. These numerical investigations are also used to verify critical experimental operating parameters that affect the performance of the tube furnace and understand the modus operandi of the tube furnace toxicity method. Copyright © 2011 John Wiley & Sons, Ltd.     

A generalized relationship between the normalized yields of carbon monoxide and hydrogen cyanide

Experimental studies have demonstrated that there are close correlations between the normalized yields of carbon monoxide (CO) and hydrogen cyanide (HCN) from the combustion of materials containing nitrogen. In this paper, a generalized relationship using the stoichiometric oxygen to fuel mass ratio (SOFMR) is derived to represent these correlations. Using this generalized relationship, the predicted yields of HCN for nylon in tube furnace experiments and HCN concentrations in full‐scale cable fire tests are in good agreement with the corresponding measured data. The derived relationship is used to analyse the contributions of CO from different materials in a complex fire reconstruction. The generalized relationship is then used to predict HCN concentrations in two full‐scale nylon fires and the predicted concentrations are compared with both experimental data and predictions from a flamelet model. Finally, a method to incorporate the generalized relationship within CFD fire simulations to determine HCN (or CO) concentrations based on measurements of CO (or HCN) yields is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

Detailed study of distribution patterns of polycyclic aromatic hydrocarbons and isocyanates under different fire conditions

This study has examined the distribution patterns between gas phase and particle phase of some chemical compounds produced in fires. It has also addressed the question of the distribution of individual particle‐associated species between the different size‐ranges of particles. The chemical compounds studied and discussed in this paper are polycyclic aromatic hydrocarbons (PAHs), and isocyanates. The steady‐state tube furnace, ISO/TS 19700, was chosen as the physical fire model in order to study the production of particles from different types of fire exposure, that is, oxidative pyrolysis, well‐ventilated flaming fires and under‐ventilated flaming post‐flashover fires. Two materials were chosen for investigation, a polyvinyl chloride ( PVC) carpet and a wood board. The particle production from the two materials investigated varied concerning both the amounts produced and the particle size distributions. The analysis of PAHs showed that volatile PAHs were generally dominant. However, when the toxicity of the individual species was taken into account, the relative importance between volatile and particle‐associated PAHs shifted the dominance to particle‐bound PAH for both materials. The substantial degradation in the tests of the low polyurethane content of the PVC carpet, and the (4,4′‐methylenediphenyl diisocyanate)‐based binder in the wood board resulted in no or very small amount of quantifiable diisocyanates. Copyright © 2013 John Wiley & Sons, Ltd.     

Cable tray fire tests in a confined and mechanically ventilated facility

Cable fires are one of the main fire hazards in nuclear power plants. As part of the cable fire spreading (CFS) campaign of the OECD PRISME‐2 programme, 3 real‐scale cable tray fire tests were performed in open atmosphere (1 CFS support test, named CFSS‐2) and in a confined and mechanically ventilated facility (2 CFS tests, named CFS‐3 and CFS‐4). This study aims at investigating the effects of confined and ventilated conditions on cable tray fires that used a halogen‐free flame retardant cable‐type. The CFS‐3 and CFS‐4 tests involved 2 ventilation renewal rates of 4 and 15 h^?1, respectively. The confined conditions lead to decrease the fire growth rate and the peaks of mass loss rate and heat release rate, compared with open atmosphere. The reductions are larger for the lower ventilation renewal rate. Furthermore, it is shown that the CFS‐4 test may be classified as a well‐ventilated fire and the CFS‐3 test as an under‐ventilated fire. For this last one, its fire characteristics and its consequences in the fire room highlight an oscillatory behaviour, with the same low frequency, for about 30 minutes. These oscillations arise from successive combustions of unburnt gases.     

Horizontal cable tray fire in a well‐confined and mechanically ventilated enclosure using a two‐zone model

Electrical cable trays are used in large quantities in nuclear power plants (NPPs) and are one of the main potential sources of fire. A malfunction of electrical equipment due to thermal stress for instance may lead to the loss of important safety functions of the NPPs. The investigation of such fires in a confined and mechanically ventilated enclosure has been scarce up to now and limited to nuclear industry. In the scope of the OECD PRISME‐2 project, the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) conducted more than a dozen fire tests involving horizontal electrical cable trays burning either in open atmosphere or inside mechanically ventilated compartments to investigate this topic. A semi‐empirical model of horizontal cable tray fires in a well‐confined and mechanically ventilated enclosure was developed. This model is partly based on the approach used in FLASH‐CAT and on experimental findings from IRSN cables fire tests. It was implemented in the two‐zone model SYLVIA. The major features of the compartment fire experiments could then be reproduced with acceptable error, except for combustion of unburned gases. The development of such a semi‐empirical model is a common practice in fire safety engineering concerned with complex solid fuels.     

Characterization of the combustion products in large‐scale fire tests: comparison of three experimental configurations

The storage of large amounts of polymers and other bulk chemicals is a potential hazard in the case of fire. There is at present a lack of knowledge about the implications of such fires. In particular the role of the ventilation conditions on fire chemistry has warranted investigation. A set of indoor, large‐scale combustion experiments, conducted on five different materials is described in this article. The main test series was conducted using the ISO 9705 room, where both well‐ventilated and under‐ventilated conditions were attained by restricting the opening of the room. The degree of ventilation was determined using a phi meter. Furthermore, in addition to measuring the traditional fire‐related parameters, extensive chemical characterization of the combustion products was made. Two additional series of experiments were also performed. In one series of tests the size of the enclosure was increased and the fuel was placed in a storage configuration to simulate a real storage situation. In the other test series, three of the materials were tested as large‐scale open pool fires. The results from the three configurations are compared regarding yields of combustion products as a function of the degree of ventilation. For a number of toxic combustion products a clear dependence of the production on the equivalence ratio was found. Further, placing the fuel in a storage configuration did not significantly change the outcome of the combustion. Thus, the ISO 9705 room is of a size and scale that can be taken as a model for representing real‐scale fires. Additionally it has been demonstrated that an advantage of the ISO 9705 room is the ability to alter the ventilation conditions. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

Particles from fires—a screening of common materials found in buildings

Small combustion generated particles are known to have a negative impact on human health and on the environment. In spite of the huge amount of particles generated locally in a fire accident, few investigations have been made on the particles from such fires. In this article, 24 different materials or products, typically found in buildings have been exposed to burning conditions in order to examine their particle generating capacity. In addition, a carbon fibre based composite material was tested in order to investigate if asbestos‐resembling particles could be generated in a fire situation. The majority of the experiments were performed in the small‐scale cone calorimeter, and some further data were collected in intermediate scale (SBI) and full scale (room‐corner) tests. Additional testing of the composite material was made in a small‐scale tubular reactor. The amount of particles and particle size distributions were measured by the use of a low‐pressure impactor and particle aerodynamic diameter sizes from 30 nm to 10 μm were measured. The results from the project show that the yield of particles generated varied significantly between materials but that the shape of mass and number size distributions were very similar for all the materials tested. The maximum amount of particles was obtained from materials that did not burn well (e.g. flame retarded materials). Well‐burning materials, e.g. wood materials, tend to oxidize all available substances and thereby minimize the amount of particles in the smoke gas. It was found that asbestos‐resembling particles could be produced from under‐ventilated combustion of the composite material tested. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

Evaluation of polymer combustion and fire retardance by using thermography

The temperature distribution in the condensed and gas phase during combustion of polymer materials in fire tests was measured by means of thermography. It is shown that these data are very useful for mechanistic rationalization of the diagnostically poor, fail-pass rating of most of these tests. Preliminary data were obtained for polymer materials, fire retarded or not, burning in the widely used Glow Wire and UL 94 tests. It is shown that the relative fire hazard and test rating may depend strongly on the combustion parameter on which the rating is based. Furthermore, detailed data on temperature distribution are helpful in eliminating intrinsic ambiguity of the UL 94 classification in the case of fire-retarded materials burning with dripping.     

Fire calorimetry relying on the use of the fire propagation apparatus. Part II: burning characteristics of selected chemical substances under fuel rich conditions

The paper focuses on the detailed characterization of ventilation controlled fires of industrial products that are likely to govern accidental fire scenarios in fire resistant enclosures. Results regarding under‐ventilated fires of substances that are not polymers are presented to illustrate the capability of the fire propagation apparatus (FPA) to qualify such types of fires. Based on results from heptane fire tests in both well‐ and under‐ventilated fire conditions, a set of recommendations was previously provided in order to check the validity of the experimental results. The application of these recommendations is illustrated for the selected liquid substances containing hetero‐atoms. It emerges that the fire propagation apparatus assesses quite easily the performance of well‐controlled fires in both well‐ and under‐ventilated conditions. Another major outcome of our work is that the potential of the FPA has the capability to address fire issues outside the conventional use of the equipment, in particular to qualify the burning behaviour of chemicals on the full spectrum of ventilation conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Toxicity of the pyrolysis and combustion products of poly(vinyl chlorides): A literature assessment

Poly(vinyl chlorides) (PVC) constitute a major class of synthetic plastics, Many surveys of the voluminous literature have been performed. This report reviews the literature published in English from 1969 through 1984 and endeavors to be more interpretive than comprehensive. PVC compounds, in general, are among the more fire resistant common organic polymers, natural or synthetic. The major products of thermal decomposition include hydrogen chloride, benzene and unsaturated hydrocarbons. In the presence of oxygen, carbon monoxide, carbon dioxide and water are included among the common combustion products. The main toxic products from PVC fires are hydrogen chloride (a sensory and pulmonary irritant) and carbon monoxide (an asphyxiant). The LC₅₀ value calculated for a series of natural and synthetic materials thermally decomposed according to the NBS toxicity test method ranged from 0.045 to 57 mg l^?1 in the flaming mode and from 0.045 to > 40 mg l^?1 in the non-flaming mode. The LC₅₀ results for a PVC resin decomposed under the same conditions were 17 mg l^?1 in the flaming mode and 20 mg l^?1 in the non-flaming mode. These results indicate that PVC decomposition products are not extremely toxic when compared with those from other common building materials. When the combustion toxicity (based on their HCI content) of PVC materials in compared with pure HCI experiments, it appears that much of the post-exposure toxicity can be explained by the HCI that is generated.     

Limitations of using combustion toxicity testing for product selection

During the last two decades there has been considerable concern about the combustion toxicity of synthetic materials such as PVC, and about their impact on overall fire hazard. Studies using many different methodologies have shown that the combustion toxicity of PVC is not unusual, but is comparable to many natural and synthetic materials. Because of various limitations, these tests have not been considered useful for code setting or regulatory activities. Furthermore, it has been emphasized that combustion toxicity is only one of many factors which must be evaluated in determining the fire hazard of a material. Still, the fact remains that PVC has performed favorably under many different conditions.     

The corrosiveness of fluoride-containing fire gases on selected steels

Combustion gases were produced from several cable-insulation materials in separate experiments conducted in a model fire chamber. These gases were then allowed to interact with stressed metal specimens, consisting for the most part of various stainless and hardened steels as well as of carbon steel and stainless steel sheet. Thereafter the samples as exposed were stored in a humid atmosphere. As expected, PVC combustion gases caused the cracking of spring steel and also extensive pitting corrosion of stainless steel. These results confirmed that test conditions conformed to real-life fires as observed in practice. The combustion gases deriving from fluorinated polymers were much less corrosive on stainless steel and provoked only slight pitting in isolated cases. The rate of corrosion damage on carbon steel was lower by more than an order of magnitude than in the case of PVC. However, stress corrosion of sensitized 18/8 stainless steel and spring steel was found to occur. Tests on the thermal degradation of the dluorinated polymer ‘Teflon’ FEP and ‘Tefzel’ confirmed their high stability. If one compares the behaviour of these fluoroplastics with that of PVC it can generally be concluded that, although the use of fluorinated insulation materials on cables might not altogether eliminate corrosion problems in the event of fire, it does constitute a realistic contribution to fire protection and to the reeducation of fire-related damage.     

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.     

Fire spread from an open‐doors electrical cabinet to neighboring targets in a confined and mechanically ventilated facility

Electrical cabinet fire is one of the main fire hazards in nuclear power plants. As part of the OECD PRISME‐2 programme, four fire tests were carried out to investigate the fire spread from an open‐doors electrical cabinet to overhead cable trays and adjacent cabinets in a confined and mechanically ventilated facility. These tests, named CFS‐5 to CFS‐7 and CORE‐6, used same both cabinet (fire source) and three overhead cable trays. The trays were filled with a halogenated flame‐retardant cable‐type for CFS‐5 and one halogen‐free for the three other tests. Moreover, fire dampers were used for CFS‐7 test while CORE‐6 test implemented two additional cabinets adjacent to the fire source. Measurements such as flame and gas temperature, gas concentration, mass loss rate, and heat release rate were performed for investigating the fire spread. Cabinet fire spread to the cable trays for CFS‐5 and CFS‐6 tests. Three fast and short cable tray fires were shown for CFS‐5, while a slow and long cable tray fire was highlighted for CFS‐6. In contrast, the fire dampers shutdown for CFS‐7 test prevented ignition of the overhead cables. Furthermore, for CORE‐6 test, cabinet fire spread to the adjacent cabinets, but the upper cables were not ignited.     

Fire and flame retardants for PVC

The flammability performance of PVC plays a significant role in its selection for many applications. Its relatively high chlorine content (56.8%) makes it more resistant to ignition and burning than most organic polymers. In the case of flexible PVC, the plasticizers that contribute flexibility in most instances detract from its resistance to fire. To meet specifications such as oxygen index, heat release, smoke evolution, or extent of burning in cable tests, flame‐retardant (FR) and smoke‐suppressant (SS) additives are often incorporated. Synergistic combinations of FR and SS additives help PVC formulations meet many stringent FR specifications cost effectively.