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.     

Do open flame ignition resistance treatments for cellulosic and cellulosic blend fabrics also reduce cigarette ignitions?

Mattresses/bedding and upholstered furniture are subject to ignition by cigarettes (smoulder) and open flames leading to injuries, fatalities and property damage. There are mandatory and voluntary cigarette ignition standards in the USA for mattresses (16 CFR 1632) and upholstered furniture (UFAC voluntary standards) as well as open flame ignition standards in California (TB 117) and the UK (BS 5852). Open flame ignition standards are being considered/developed for these products. Some suggest that fire retardant (FR) treatments to prevent/reduce open flame ignitions also reduce cigarette ignitions. Some reports suggest that the smoulder ignition propensity of some cellulosic fabrics can be affected adversely by open flame ignition resistance treatments. Ignitions caused by cigarettes and open flames result from different types of combustion that are retarded by different mechanisms. Flaming combustion is a gas phase reaction and occurs when heat causes degradation of the polymer releasing volatile products that undergo rapid oxidation in the air, whereas smouldering combustion is a direct oxidation of either the polymer or its char. The results of textile/fibre industry studies with FR treated upholstery fabrics and a critical review of the available published literature indicate that cigarette ignition propensity of cellulose fabrics is complicated and affected by many factors and that smoulder ignition resistance of these fabrics can be affected adversely by open flame ignition resistance treatments. Copyright © 2004 John Wiley & Sons, Ltd.     

The combustion toxicity controversy

As long as 20 years ago the need was considered to extend codes concerned with flammability and/or flame spread, to include combustion toxicity requirements. Due to the lack of suitable toxicity tests at that time, the added code requirements for combustion toxicity were not enforceable. Vinyl resin manufacturers have been cited as purveyors of hazardous materials which, when burned, generate a noxious toxic hazard due to the fumes they produce in a fire. Overlooked are such factors that commercial vinyl products have inherent low ignition and flame spread rates and only generate potentially toxic gases when quantities of other materials burning around them heat the vinyls to the decomposition point. In 1983 New York State commissioned a study by A. D. Little Inc. to assess the feasability of incorporating combustion toxicity requirements into building material and furnishing codes of New York State. This paper summarizes these findings, including evaluation and analysis of the data generated by the two tests selected as best meeting the seven critical criteria. Due to differnt combustion toxicity rankings provided by the two test methods, controversial and confusing interpretations reign. As a result, the author provides a four step set of recommendations.     

Flammability limits of some polymer pyrolysate–air mixtures

Several textile fabrics have been heated in a closed cell and the flammability limits of the gaseous products produced determined. In addition the energy released on combustion of these gaseous products has been measured in order to obtain an indication of the heat feedback capabilites of the fabric. Comparison of the data obtained was made in order to provide an indication of the flash fire potential of the materials and their contribution to a potential fire hazard situation.     

Experimental study on polystyrene with intumescent flame retardants from different scale experiments

In this study, the fire performance and toxicity of intumescent flame retardant (IFR) polystyrene composites were investigated experimentally. Ammonium polyphosphate, pentaerythritol, and melamine were selected as IFR. The flammability of the polystyrene (PS) composites was evaluated by microscale combustion calorimetry and cone calorimetry and in the ISO Room. The results suggested that the thermal stability and the peak heat release rate of PS composites decreased with the increasing content of IFR. In the cone calorimeter and ISO 9705 testing, the carbon monoxide yield of PS composites also decreased markedly with the addition of IFR. Scanning electron microscope images show that the char from cone calorimetry testing was more compact and smoother than that from the ISO 9705 testing. The comparison between bench‐ and full‐scale tests demonstrated that the flammability and the toxicity of PS composites are decreased markedly due to the incorporation of the flame retardant, but considerable differences exist. Copyright © 2014 John Wiley & Sons, Ltd.     

An experimental study of flammability limits of LPG/air mixtures

The liquefied petroleum gas (LPG) is generally considered to be eco-friendly viable fuel not only in domestic sector but also for transport sector. The inhibition of LPG-air premixed flames is a very important practical problem that has received relatively little attention. This paper is concerned with experimental determination of the flammability limits of LPG-air mixture. The standard procedure suggested by US Bureau of mines has been adopted for the present studies for determining the flammability limit of LPG-air mixture. The lower flammability limit (LFL) is found to be 1.81% and upper flammability limit (UFL) is 8.86% of LPG for upward propagation of flame. Whereas, for downward propagation of flame, the LFL and UFL are 1.87 and 7.69% of LPG, respectively. The nitrogen dilution effects on the flammability limits have been explored, which is presented on a flammability limit plot. It is believed that these data will be very useful for developing fire extinguishers and other combustion devices.     

Protective clothing: Evaluation of zirpro wool and other fabrics

Protective clothing against head and flames should be evaluated not only for flame retardance but also for protection against various heat exposure from convection (flames), conduction (molten metal splashes) and radiation sources, depending on the end use, to ensure a realistic assessment of the potential protection offered and required. Evaluations of various flame-retardant fabrics to different heat exposures showed that the fibre and the flame retardant finish should preferably form a well developed char on exposure to heat, without softening and melting. The flame retardant should act in the solid phase and the fibre should be of low thermal conductivity. For protection against convective heat (flames), a woven Zirpro wool fabric of high density over a bulky knitted Zirpro wool underwear fabric offered a significantly better protection than a single layer of a woven or knitted fabric or a double layer of a woven fabric of the same total weight. The optional multi-layer fabric approach could also decrease overall garment weight and improve wearers' comfort without adverse effect on the protection offered. Of the FR fabrics evaluated, Zirpro wool fabric assemblies showed the longest time to reach pain (first degree burn) and blister (second degree burn) thresholds, as well as the longest pain alarm time–the time available to the wearer to withdraw from the flame heat source before serious injuries occur. Zirpro wool fabric assemblies had one of the lowest residual heat transfers after al limited flame exposure to the pain threshold while some other fibres, e.g. aramid and novoloid, transferred significant residual heat, possibly causing second degree burns. For protection against conduction, such as from molten aluminium splashes, the fabric should have a smooth surface, high density and thickness, besides the other previously mentioned, basic requirements. Zirpro wool fabrics offered a significantly better protection in this case than aramid, FR cotton, glass fibre, asbestos, and other FR fibres. Aluminized fabrics are essential for adequate protection against radiant heat and the aluminization technique affects heat transfer significantly. A low density base fabric made from a fibre of low thermal conductivity, such as Zirpro wool, reduces heat transfer in this case.     

Fire behaviour of upholstered furniture—an experimental study

A series of experiments for studies of flammability characteristics of upholstered furniture is presented. The series comprises 53 experiments on a reduced scale and 11 full-scale experiments in an extensively instrumented room. Results are presented from measurements of rate of heat release and smoke production. The experiments indicate that ignitability can be considerably decreased by careful choice of the upholstery materials.     

Design of Hierarchically Tailored Hybrids Based on Nickle Nanocrystal-Decorated Manganese Dioxides for Enhanced Fire Safety of Epoxy Resin

A novel and hierarchical hybrid composite (MnO₂@CHS@SA@Ni) was synthesized utilizing manganese dioxide (MnO₂) nanosheets as the core structure, self-assembly chitosan (CHS), sodium alginate (SA) and nickel species (Ni) as surface layers, and it was further incorporated into an epoxy matrix for achieving fire hazard suppression via surface self-assembly technology. Herein, the resultant hybrid epoxy composite possessed an exceptional nano-barrier and synergistic charring effect to aid the formation of a compact layered structure that enhanced its fire-resistive effectiveness. As a result, the addition of only 2 wt% MnO₂@CHS@SA@Ni hybrids led to a dramatic reduction in the peak heat release rate and total heat release values (by ca. 33% and 27.8%) of the epoxy matrix. Notably, the peak smoke production rate and total smoke production values of EP/MnO₂@CHS@SA@Ni 2% were decreased by ca. 16.9 and 38.4% compared to the corresponding data of pristine EP. This was accompanied by the suppression of toxic CO, NO release and the diffusion of thermal pyrolysis gases during combustion through TG-IR results. Overall, a significant fire-testing outcome of the proposed hierarchical structure was proven to be effective for epoxy composites in terms of flammability, smoke and toxicity reductions, optimizing their prospects in other polymeric materials in the respective fields.     

Flammability characteristics of fiber reinforced organic matrix composites

The effect of resin, fiber, and fire retardant additives on flammability characteristics of organic matrix composites was evaluated. Information is presented on the flame spread index, determined by the radiant panel test, the amount of smoke generated, and products of combustion, using the National Bureau of Standards Smoke Density Apparatus, and the amount of oxygen required to support combustion using the Oxygen Index method. These methods were effective in screening the flammability characteristics of organic matrix composites. Of the materials evaluated the polyimide composites were the most resistant to flame spread, exhibited the lowest evolution of smoke and toxic products and had the highest oxygen index. No differences in flame spread and oxygen index were observed for the polyester epoxy glass-cloth laminates. Addition of antimony trioxide and hydrated alumina to the polyester and epoxy resin systems significantly decreased the flame spread index and increased the oxygen index, but showed a marked increase in smoke evolution. Smoke properties depended on resin content whereas the type of reinforcement did not appear to affect flame spread index or smoke properties. The use of protective barriers in selected shipboard areas can reduce flame spread and lengthen the lime for generation of smoke.     

Structure of lean premixed hydrogen-air flames in an annular microcombustor

Self-sustainable combustion and narrow stability limits are the most critical issues in microcombustors (length scale 1 mm) as increased heat losses can lead to thermal quenching of the flame. Hydrogen is a potential fuel for microcombustion due to its high specific energy and wide flammability limits. This work focuses on the lean premixed hydrogen-air flames stabilized in a newly developed annular microcombustor. Detailed axisymmetric numerical calculations involving multistep kinetics, multicomponent mass-heat transport, conjugate heat transfer, and thermal radiation in gas and solid media are performed. It has been shown that flame stabilization occurs by preheating even though wall temperatures are higher than the autoignition temperature. Results unravel the importance of H radical reactions in the kinetics of microflames in low- and high-temperature regions of the microcombustor.     

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     

Effects of oily contamination and decontamination on the flame resistance of thermal protective textiles

This paper reports an experimental study wherein flame resistance and limiting oxygen index of protective fabrics were determined before and after contamination with oil and after decontamination. Experimental variables were presence of contamination, laundry treatment, number of contamination/decontamination cycles, and fabric type. Although laundering with pre‐wash products alone was the most effective in removing oil, some product residues may have contributed to the increased flammability of some fabrics. Thus, use of that product was truly effective only if combined with detergent. For two fabrics higher flammability was noted after five contamination/decontamination cycles than after one. Of the three fabrics studied, aramid specimens retained the least oil, and although they had the highest flammability both before and after contamination, it increased the least with contamination. The FR cotton/nylon fabric retained the most oil after decontamination, but had better flame resistance than aramid. Much of the oil remained in the interior of cotton fibres making it difficult to remove but also less accessible for vaporization and combustion. For the aramid/FR viscose, energy from combustion of residual oil activated the FR additive, thereby reducing apparent fabric flammability, but this FR transference effect occurred only up to an optimum quantity of oil. Copyright © 2010 John Wiley & Sons, Ltd.     

A molecular basis for polymer flammability

Empirical molar group contributions to the thermal combustion properties measured by microscale combustion calorimetry were determined by multiple linear regression of data for engineering polymers of known chemical composition. Char yield, heat of combustion and heat release capacity of polymers calculated from their chemical structure using optimized additive molar group contributions were in reasonable agreement with measured values for these properties. The relationship between the thermal combustion properties and the results of standardized flame and fire tests (i.e., flammability) was examined statistically for an expanded data set.     

Effect of inhibitors on flammability range of flames produced from LPG/air mixtures

Burning velocities of Liquefied Petroleum Gas/air flames of different fuel/air compositions have been measured by the flat-flame method originally developed by Egerton and Powling, and the effects of inhibitors such as chlorinated hydrocarbons (chloroform, methylene dichloride, carbon tetrachloride) on the burning velocities have been investigated. The flammability limits at different fuel/air compositions have also been measured. The difference between upper and lower limits of flammability was narrowed by the addition of inhibitors in the order carbon tetrachloride chloroform methylene dichloride, i.e. the inhibiting effect increased with increase in the number of chlorine atoms. The relative effectiveness of different inhibitors has been expressed as an inhibition efficiency, and it has been found that an interesting correlation exists between the inhibition efficiency (also the narrowing of limits, and the maximum burning velocity) and the number of (dissociable) chlorine atoms present in the molecule of inhibiting compound. Other factors were the degree of dissociation of the inhibiting molecule in the flame, and the concentration of the inhibitor in the fuel/air mixture; the effect of small concentrations was that of specific chemical inhibition whereas at higher concentrations dilution effects were dominant. At the upper limit the flame has maximum tendency to flash back in an ordinary burner and the combustion wave may develop into a detonation wave inducing an explosion hazard. Hence upper explosion limit may be considered an index of explosion risk. The inhibitors lower this largely by reducing the concentration of free radicals in the flame boundary, increasing the difficulty of ignition, and thus increasing safety. A large difference has been found between the experimental and calculated value of the upper limit for the pure gas, probably owing to the chemical effects of ethylene via production of acetaldehyde which catalyses the combustion.     

Heat release rate in evaluation of conveyor belts in full-scale fire tests

The theoretical bases for calculation of heat release rate during burning of conveyor belts in the fire-testing gallery has been presented. Taking as an example the results of measurements of oxygen, carbon dioxide and monoxide content in the products of combustion of conveyor belts during the testing of their flammability in the full-scale fire gallery, the possibility has been demonstrated for using the calculations of heat release rate in an assessment of conveyor belt flammability. The total quantity of heat released during the belt fire in the experimental gallery can provide the basis to develop a new method of testing as well as the criteria for assessment of fire resistance of the conveyor belts using oxygen consumption calorimetry. © 1997 John Wiley & Sons, Ltd.     

Gas combustion in a narrow channel at high pressure

This paper presents experimental results on the effect of pressure on the flame propagation velocity in a tube with diameter close to the critical diameter. An important feature of the investigated combustion regime is heat transfer along the tube wall from the combustion products to the fresh mixture. Methane-air and hydrogen-air mixtures were used. The experiments show that with increasing pressure, the burning velocity of methane-air flames decreases whereas the burning velocity of hydrogen-air flames is almost unchanged. This behavior is explained by the pressure dependence of the laminar burning velocity.     

Using heat of combustion data to estimate or assess some threshold flammability properties of materials

This paper gives a brief summary of recent studies using heat of combustion data to estimate or assess some threshold flammability properties of materials. Heat of combustion data can be used to estimate the lower flammability limit, upper flammability limit and minimum oxygen concentration for flame propagation of organic and organosilicon compounds. The data can also be used to assess the threshold oxygen pressure for the combustion of metal alloys in high‐pressure oxygen environments. Copyright © 2003 John Wiley & Sons, Ltd.     

Upper flammability limits of some organosilicon compounds

This paper reports the upper flammability limits of 26 organosilicon compounds commonly used in the silicone industry and investigates the correlation between the upper flammability limit and the net heat of combustion. An empirical equation has been developed to predict the upper flammability limit of organosilicon compounds using the net heat of combustion. Copyright © 2004 John Wiley & Sons, Ltd.     

Reducing the flammability of ultra-high-molecular-weight polyethylene by triphenyl phosphate additives

The thermal degradation and combustion of ultra-high-molecular-weight polyethylene (UHMWPE) doped with triphenyl phosphate (TPP) at atmospheric pressure was studied by molecular beam mass spectrometry, dynamic mass spectrometric thermal analysis, microthermocouples, thermogravimetry, gas chromatography/mass spectrometry. The kinetics of thermal degradation of pure UHMWPE and that mixed with TPP at high (≈150 K/s) and low (0.17 K/s) heating rates was investigated. The effective values of the rate constant and activation energy of the thermal degradation reaction were determined. Burning velocity and temperature profiles in UHMWPE and UHMWPE + TPP flames were measured. The composition of the combustion products in a flame zone adjacent to the burning surface of the sample was determined. TPP vapor in the flame was detected. The addition of TPP to UHMWPE was found to reduce the flammability of the polymer. It is shown that TPP acts as a fire retardant in both the condensed and gas phases.