Showing papers in "Fire and Materials in 1982"

Development of the cone calorimeter—A bench-scale heat release rate apparatus based on oxygen consumption†

Abstract: A new bench-scale rate of heat release calorimeter utilizing the oxygen consumption principle has been developed for use in fire testing and research. Specimens may be of uniform or composite construction and may be tested in a horizontal, face-up orientation, or, for those which do not melt, in a vertical orientation. An external irradiance of zero to over 100 kW m−2 may be imposed by means of a temperature-controlled radiant heater. The rate of heat release is determined by measuring combustion product gas flow and oxygen depletion, while the mass loss is also recorded simultaneously. The instrument has been designed to be capable of higher accuracy than existing instruments and yet to be simple to operate and moderate in construction cost. The instrument is thermed a ‘cone calorimeter’ because of the geometric arrangement of the electric heater.

A mathematical model for estimating available safe egress time in fires

Abstract: A mathematical Model for estimating the time available for safe egress from a fire is formulated. The model simulates the conditions which develop during the course of an enclosure fire. Since life safety considerations are primary, the simulation model which is adopted focuses attention only on phenomena which develop between the times of fire ignition and onset of hazardous conditions. This allows significant simplifications in modeling which may not be otherwise justified. Using computed variables of a simulated fire scenario of interest, times of fire detection and onset of hazard which are deduced from realistic detection and hazard criteria would be estimated. The Available Safe Egress Time (ASET) would be defined as the length of the time interval which separates these two events. Quantitative specifications for a variety of detection and hazard criteria are identified. Results of exercising the model are presented, and ASET estimates are obtained for a wide variety of realistic fire scenarios. A comparison between experimental results of a multi-room fire test and prediction of the single-room model suggest that the model has potential utility in providing practical simulations of multi-room fire environments.

An analysis of smoldering fires in closed compartments and their hazard due to carbon monoxide

Abstract: A review was made of smoldering fire experiments conducted in closed rooms and buildings. The results were summarized by tabulating maximum levels of CO, the time integral of CO concentration (‘dose’), CO2, temperature rise and oxygen consumption. A hazard time based on the attainment of a CO dose equal to 4.5% CO-minutes and the time for transition to flaming were also tabulated. The likelihood of reaching a critical CO condition during smoldering seems to be comparable with the likelihood of having transition to flaming occur. A theoretical model, requiring inputs of CO production rate and energy release rate, was executed and compared with available data. The theoretical results for CO concentration as a function of time were in good agreement with the experimental data. The model offers a means of extrapolating test data to compartments of various size in order to assess the general hazard of CO due to smoldering.

Smoke Measurements: An Assessment of Correlations Between Laboratory and Full-Scale Experiments

Abstract: An extensive review is presented demonstrating the nature of comparison between full-scale fire smoke data and test method results for materials. These correlations are presented in terms of consistent parameters established through a development of the governing equations for smoke concentration and light attenuation. Visibility data limited to light transmission through smoke are also presented. The complex dependence of smoke production on many parameters acting in fire growth limits the success of simple correlation methods. Recommendations are made for further research to establish a sound basis for correlations, and the prediction of smoke obscuration due to fire.

Some stochastic properties of fire plumes

Abstract: Reaction to fire tests are the main criteria used by legislators of fire regulations to determine the suitability of different materials for use in building construction. These do not always give reliable results, particularly when applied to new man-made materials. Part of the explanation for this is the lack of detailed understanding of the heat and mass transfer processes occurring in fire. This is in part due to a lack of measurements of the fluctuating property field in the source plume. In this paper measurements of the probability density functions, spectra and mean square fluctuations of temperature together with the probability of combustion are reported for a stimulated fire plume. The results are consistent with the model of a fire comprising a series of narrow flame fronts oscillating at the flame flicker frequency (which for this system is 3 Hz). The effects of thermal inertia in thermocouples on the determination of mean and fluctuating gas temperature have been examined using the treatment of Ballantyne, Boon and Moss. The high-frequency limitations of thermocouple and electrostatic probes have been discussed in the context of trubulent filed measurements in fires.

Action of phosphorus compounds on fire-retardancy of cellulosic materials: A review

Abstract: Owing to their low cost phosphorus fire-retardants find vast application in making fire-retardant cellulosic compostions. They have been used both as a physical additive as well as part of the polymer structure. Acid forming phosphorus compounds are generally effective in cotton and other cellulosic. Acidic retardants produce char via a dehydration process and this brings about the final fire-retardancy in phosphate-containing composition. High efficiency of phosphorus fire retardants in polyurethane foam has also been suggested to be the result of stable char formation. The char affects the flammability in the three following ways: reduction of flammable fuel, insulation by the char and coating by the non-volatile thermally stable phosphorous acids which screen the hot carbon from the oxygen. Nitrogen-phosphorus synergism in cellulose in controversial and evidence indicates that it is non existent in polymers.

The Role of Nitrogen in Nitrogen Phosphorus Synergism

Abstract: Thermal analysis and limiting oxygen index flammability tests were used for elucidation of details in phosphorous-nitrogen synergism in cotton modified with methylol phosphonopropionamide and subsequently hydrolyzed by acid. The results indicate that not all the phosphorus incorporated into the material is effective for flame retardancy purposes in the condensed phase. The comparison of modified and acid hydrolyzed cotton has shown the important influence of nitrogen in the structure of the flame retardant. A simplified theory of nitrogen-phosphorus synergism, considering this influence, is proposed.

Normalized heat load: A key parameter in fire safety design

Abstract: It is demonstrated that he normalized heat load is a suitable parameter for ranking various enclosure fires on a ‘potential for destruction’ scale. This parameter is convertible to the familiar fire resistance.

Modeling of NBS Mattress Tests with the Harvard Mark-V Fire Simulation

Abstract: NBS burned eleven mattresses made up with bedding in two different rooms, typical of a residential bedroom and a nursing home patient room, respectively. Seven of the mattresses flamed and burned vigorously, the other four were of a construction or so heavily flame-inhibited that they only smoldered. The burning behavior of the seven that flamed was modeled with the Harvard Mark V fire simulation. The experimental burn behavior for tests conducted in one room was well reproduced using only total weight of combustible, surface area and heat of combustion. Smoke production values were found to have little effect on the predicted behavior except for the smoke production itself. Fires in a second room, whose ventilation was intentionally restricted by the configuration of the adjoining space, could not be as well reproduced by the present, single-room fire model. During this study several changes were made to the simulation. The most significant change was the inclusion of mixing of the hot exiting fire gases with the cold incoming air. As a part of this, the inter-layer radiation exchange was reformulated to include the effect of smoke contamination of the lower layer. The reformulation of the radiation model has a marked effect on the predicted upper layer gas temperatures, generally improving the quality of the simulation.

How well are we measuring smoke

Abstract: Estimates of the errors in light extinction measurements of smoke resulting from forward scattered light entering the detector and from the spectral width of the light source are presented. It is shown for specific examples that each of these effects can lead to an error of about 25% in typical applications. A potential method for calibrating extinction instruments is described.

Determination of Hydrogen Cyanide in Thermal-Degradation Products of Polymeric Materials

Abstract: Thermal degradation products of nitrogen-containing polymeric materials were analysed for hydrogen cyanide. A spectrophotometric method was used for the determination of cyanides using the formation of a characteristic absorption peak of cyanonickel(II) ion in the ultraviolet spectral region. Pyrolysis and thermooxidation products were studied and conclusions on the reproducibility of the degradation process were drawn. The effect of temperature on the quantity of hydrogen cyanide formed was studied as well.

Synergistic action of Sb2O3 with bromine‐containing flame retardant in polyolefins: 3—The relationship between certain combustion variables

Abstract: The combustion of polypropylene flame-retarded by the synergistic action between Sb2O3 and bromine-containing flame retardants has been studied. From the relationship between a number of the variables, a parameter quantatively reflecting the flame retardant effect has been found. With the addition of flame retardant, the rate of weight loss, the CO and CO2 emission rates and heat release all decrease while smoke density increases. These effects were considered to depend on the concentration of HBr gas in the pyrolysates released into the gas phase (i.e., dWHBr/dW, HBr flux ensity), and the following equations were obtained: η*(dW/dt)max, which approximately corresponds to the oxidation velocity of pyrolized hydrocarbon, is inversely proportional to the HBr flux density. As the conversion of CO to CO2 was almost independent of the amount of flame retardants added, the flame retardant effect of bromine-containing flame retardants was considered to be a retardant effect of the initial oxidation reaction at the gas liquid interface. Moreover, η* is almost proportional to the combustion efficiency η, which was obtained from the heat release measured in the flaming region. The heat release is therefore considered to be governed by the HBr flux density.

The Delphi method—a complement to research

Abstract: In making fire safety decisions the designer often finds that some input variables concerning his problems are chance variables. As detailed statistical data are rarely available the designer must rely largely on his expert judgment. With the application of the Delphi method such decisions can be optimized and formalized. The essence of the Delphi method is described and its use illustrated through an example related to the assessment of fire resistance requirements.

Development of an Improved Radiant Heat Source for Fire Testing

Abstract: The development, construction, and testing of a gas-fired radiant heat source for use as part of a fire test method is described. The unit has been shown capable of operation over extended periods at surface temperatures yielding radiance corresponding to that of a black body at 935 °C. This permits a 60% increase of specimen irradiance over that possible with a burner previously used, without modifying the specimen–burner configuration factor. One such application of this burner allows operation with specimen irradiance levels at 5 W cm−2 or for short periods at levels approaching 7 W cm−2 at higher temperatures. This performance is achieved while maintaining effective spatial separation between specimen and heat source. This assists in avoiding imposition of vitiated air near the surface of a burning specimen. Some performance data are provided on its behavior when supplied with natural gas. The unit can burn propane but only with a significant reduction of thermal output.

Textile Flammability Testing: Appropriate Levels for Moisture Content of Specimens

Abstract: This study was performed to establish the appropriate moisture level for textile flammability test specimens. Three investigations were carried out: into the effect of the level of humidity in dwellings; into the moisture content of garments worn at various distances from the body; and into the effect of relatively short exposures to heat on the moisture content of fabrics (simulating the case of a person standing in front of an open fire or space heater). The moisture content of ambient air in dwellings was found to be primarily governed by the moisture content of the air outside and can be quite low, ten to twenty percent, especially in winter (unless, of course, humidifying equipment is used). The moisture content of garment parts which are at some distance from the body (e.g., the loosely fitting parts of skirts) is governed by the relative humidity of the room. Closely fitting parts are more likely to be exposed to ignition sources than closely fitting parts. Fabric specimens exposed at a short distance from an electric space heater had moisture contents similar to specimens which has been oven-dried and cooled in a desiccator. The results of these studies indicate that oven-drying is a reasonable conditioning requirement for testing the flammability of apparel and home furnishing fabrics.

The thermal behaviour of lignins modified by chlorophosphazenes

Abstract: The thermal behaviour in air of lignins modified by chlorophosphazenes as well as that of the raw materials of lignins has been investigated using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). The thermogravimetry and derivative thermogravimetry studies of lignins modified by chlorophosphazenes have shown their thermal resistance to be relatively higher than that of the intital raw materials of lignins in concrete kraft lignin and sodium ligninosulfonate. The differential thermal studies have demonstrated that the thermal degradation of products investigated takes place via exothermic processes. The lignins modified by chlorophosphazenes have been shown to be thermal and flame-resistant materials.

The thermo‐oxidative decomposition, ignition and burning of flame‐retarded polystyrenes

Abstract: The theromo-oxidative decomposition, flash ignition and burning of high-impact polystyrene containing the flame-retardant system decabromodiphenyl oxide + antimony trioxide was investigated using the Setchkin apparatus combined with mass spectrometry. The time dependences of the release rate of the main products into the gas phase during decomposition and burning showed that the flame-retardants markedly influence these processes. It was found that the retardants used exhibit an acceleration of the polymer degradation and that the efficiency of inhibition in the gas phase depends on the atomic ratio antimony: bromine.

An Investigation of the Variation of Oxygen Index of Materials with Changes in Pressure

Abstract: An apparatus has been designed and a procedure adopted for studing the oxygen index of materials over a range of pressures. It has been found that the oxygen index falls with increase in pressure so that materials become more flammable, the effect being more marked with the less flammable materials. An empirical method has been devised for predicting the oxygen index at varying pressures.

Oxidation and Stabilization of Hydrocarbon Polymers - Relationships, New Aspects and Unsolved Problems

Abstract: Oxidation processes involved in processing, atmospheric ageing and the pre-burning stages of hydrocarbon polymers are outlined. Open problems based on up-to-date knowledge of the mechanisms of oxidation and stabilization processes are considered. Stabilizers used to assist processing and long-term stability are transformed during their service-time. Some of the products thus formed, as well as the products of polymer oxidation, should be considered as inherent impurities of polymers and play an active role in the degradation. Because of safety consideration, some of the products have to be protected also against catastrophic oxidation, i.e. burning. Significant changes in the mechanisms of degradation take place in the pre-burning step in the phases of high temperature oxidation and oxidative pyrolysis. Fuller understanding of the mutual relationships in the mixtures of antioxidants and/or light stabilizers with flame-retardants in lacking.

Fire test behaviour of various crystal types of melamine phosphate in intumescent formulations

Abstract: Melamine orthophosphate crystals vary in shape and formula according to their method of production. The types vary widely in their behaviour when incorporated into an epoxy resin intumescent coating for trials in a small scale fire test. Heat treatment of melamine phosphate crystals at 210 °C, a process designed to reduce their solubility, profoundly affects the performance of any crystal type in a fire test. In such cases crystal shape alone appears to determine performance, whereas the shape, formula, and state of agglomeration affect performance in coatings produced with untreated melamine phosphate. Small plates of side 20 μm heat treated at 210 °C, are the preferred type for optimum performance and weathering characteristics.

Inorganic elements in the tracheas of fire fatalities

Abstract: Concentrations of elements were determined in tracheal specimeans of fatal fire casualties and of non-fire fatalities. Elevated concentrations of antimony, bromine, zinc, chromium, cobalt, iron, lead, cadmium and gold found in the group exposed to the fire environment were associated with deposition of soot. The presence of raised concentrations of antimony in fatalities was found to occur in association with increased content of carboxyhaemoglobin in blood and was greatest in fires involving major destruction of property. A relationship between the increased concentration of this element and the use of antimony containing fire-retardants in construction materials could not be demonstrated.

High temperature oxygen index studies of halogenated polyester thermosets containing antimony and molybdenum oxides

Abstract: A study has been made of the effect of antimony and molybdenum oxides on the temperature-critical oxygen index relationship of halogenated polyester thermosets. The polyesters were prepared from maleic anhydride, phthalic anhydride and propylene glycol, using either tetrachlorophthalic anhydride, tetrabromophthalic anhydride or chlorendic anhydride as the halogen source. Marked differences were observed in the effect of the two oxides. The critical oxygen index values of the halogenated polyesters containing maoybdenum (VI)oxide decreased with increase in timperature, which is in accordance with what is normally found for organic polymers, with and without additives. In contrast to this, the critical oxygen index values of the formulations containing antimony(II)oxide increased with increased with increase in temperature to reach a maximum value at around 100–150 °C. These results indicate that antimony(II)oxide is a better flame retardant than molybdenum(VI)oxide, since not only is it superior at the primary ignition stage but it shows enhanced activity at the higher temperatures which would be experienced by polymeric material in the early stages of a fire. It is concluded that higher temperature critical oxygen index studies provide a better guide to the flame retardant activity of additives than do ambient critical oxygen index determinations alone.

Fire safety of soft furnishings—an overview

Abstract: The fire risk posed by soft furnishings such as bedding materials and upholstered furniture and the strategies being developed to reduce the number of fire-related casualities are reviewed from a Canadian point of view. Statistics from Canada, the United States and the United Kingdom indicate that a substantial reduction in the number of fire deaths would be possible if the ability of assemblies of materials to resist ignition by smokers' materials, such as cigarettes and matches, could be improved. The post-ignition performance of furnishings that results in generation of heat, smoke and toxic gases is also important from a safety point of view. A need exists for both full-scale and small-scale fire tests, and for mathematical modelling for present and future control strategies.

A fire test device suitable for small‐scale testing of fire retardant coatings

Abstract: A fire test device suitable for small-scale, comparative testing as a first step in investigating the performance of fire retardant materials is described. The procedure developed is not intended to predict the performance of a given material in a real fire, since the local conditions can be extremely variable. However, the parameters in the device can be varied over a wide range to screen the performance of various materials in given situation. Typical results for an intumescent mastic consisting of epoxy resin, hardener and melamine phosphate are quoted, together with appropriate calibration curves. A method of estimating the thermal resistance of the developing char is also discussed.

Toxic gas tests in perspective

Abstract: 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.