The Experimental Study of Fire Behavior in a Compartment - Research Paper Example

Student Name: Tutor: Title: The Experimental Study of Fire Behavior in a Compartment Date: ©2016 Table of Contents List of Figures 1 1.Aims and Objectives 2 2.Methodology 2 2.1Ignitability of Samples based on ISO 5657:1986 2 2.1.1Overview 2 2.1.2Test concept 3 2.1.3Test Procedure 3 2.2Heat Release Rate Determination by Cone Calorimetry ISO 5660 – 1: 2002 4 2.2.1Overview 4 2.2.2The Test Concept 4 2.2.3Apparatus used 6 2.2.4Description of Samples 6 2.2.5The Test Procedure 6 2.3Smoke Production Rate 7 3.Test Results and Discussion 8 3.1Heat Release Rate 8 3.2Mass loss rate 11 3.3Total Heat Release 12 3.4Smoke Production Rate 14 4.Conclusion 16 5.References 18 Figure 2.1: Procedural Set-up 6 Figure 3.2: Rate of heat release for PMMA samples at intensity of 25kW/m2 9 Figure 3.3: Ideal fire development stages. 10 Figure 3.4: Rate of heat release for PMMA samples at intensity of 55kW/m2 11 Figure 3.5: The rate of mass loss vs time 12 Figure 3.6: Total heat release for PMMA samples at 25kW/m2 13 Figure 3.7: Total heat release for PMMA samples at 55kW/m2 14 Figure 3.8: Smoke release rate at high heat fluxes of 55kW/m2 15 Figure 3.9: Rate of smoke release at increased heat flux (55kW/m2) 16 List of Figures Figure 2.1: Procedural Set-up 5 Figure 3.1: Rate of heat release for PMMA samples at intensity of 25kW/m2 8 Figure 3.2: Ideal fire development stages. 8 Figure 3.3: Rate of heat release for PMMA samples at intensity of 55kW/m2 9 Figure 3.4: The rate of mass loss vs time 10 Figure 3.5: Total heat release for PMMA samples at 25kW/m2 11 Figure 3.6: Total heat release for PMMA samples at 55kW/m2 12 Figure 3.7: Smoke release rate at high heat fluxes of 55kW/m2 13 Figure 3.8: Rate of smoke release at increased heat flux (55kW/m2) 14 1. Aims and Objectives The main aim for this dissertation is to study the combustion behavior of compartment fires using calorimeter tests. Specifically, the paper looks into establishing a simple model of fully developed compartment fires that can be a significant tool in the prediction of the fuel mass loss rate, the rate of heat release the mean temperature for enclosed fires that are either fully or partially developed; this as a function of the fuel material type, fuel properties and layout, wall features ventilation and radiative intensity. A summary of the specific objectives is as follows; 1. To determine the burning properties of the different colors of Polymethyl methacrylate (PMMA) samples, specifically black, greed, red and white. 2. To establish the effect of different levels of radiative intensity on the colors of PMMA under study. 3. To measure and establish how easily material samples ignite when exposed to heat fluxes at different levels in the presence of a predetermined source of the ignition. 4. To plot graphs of the mass loss rate versus time, smoke production rate versus time and heat release rates for the samples used in the calorimeter tests. 5. To study the correlations that may exist between the various parameters of compartment fires and assess the importance of each in understanding the behavior of compartment fires. 2. Methodology 2.1 Ignitability of Samples based on ISO 5657:1986 2.1.1 Overview The fire ignition process is not only an important facet of fire initiation, but also plays a crucial role in development of fire, as it is an essential factor in the propagation of fire to close-by zones of the compartment or structure. ISO 5657 recommends the Ignitability Test as the basic method for determining how easily the material samples ignite when exposed to varying heat fluxes in the presence of a predetermined source of ignition. It is paramount to study the ignitability parameters of a material especially those used in construction as this would aid the accurate consideration of design parameters and in understanding their burning behaviour in case they are involved in a fire. Compartment fires are characterized by the thermal radiation as a result of heat fluxes from the burning environment and burning fuel having a significant effect on the fire growth, the propagation of the flames and the production of combustion products. As such, a relationship between the gas temperatures at maximum burning rates and the corresponding irradiance intensity can be established. 2.1.2 Test concept This test is based on the principle that materials require different levels of heat intensity to ignite. A sample of polymer material (colors of PMMA polymer) is to be tested using based on fabricated test methods. 2.1.3 Test Procedure The following is the Ignitability Test procedure that was followed in the assessment of this parameter; i. Two samples for the various colors of PMMA were used each 25kW/m2 and 55kW/m2 respectively. ii. The PMMA crib sample dimensions were as 165 by 165mm square, Depth was also determined as 5mm iii. A sample being tested was then set up on a base board and wrapped with an aluminium foil with a circular opening of approximate diameter of 140mm that is cut out from the centre of the sample iv. The following radiative features of the flame source were then set Pilot flame was adjusted to approximately 15mm. The propane flowrate was set at 20 ml/min. Ventilation air flow rate was set at 180 ml/min v. A dummy PMMA crib board was then inserted into the burning chamber and used to further adjust the Insert dummy board vi. The temperature controller was then adjusted to produce 55kW/m2, then lower to 25kW/m2. vii. The real temperature on the auxiliary thermocouple with the calibrated test values at this irradiance was checked and recorded. viii. A screen plate was then placed over the dummy board before starting the pilot flame mechanism. Upon commencing it, the dummy board was removed and replaced with the sample to be studied. ix. The screen place was then removed and the timer started. The timer would only be stopped if sustained surface ignition occurs. x. The pilot flame was then stopped and screen board replaced. The sample under study was then removed, dummy board replaced then screen board removed. xi. It is important to note that whenever there was no sustained ignition within the recommended 15minutes, (BS 476; Part 13) then the test was stopped as in procedure (x) above. xii. The temporary ignition is then noted while the test is in progress. xiii. The procedures above were then repeated twice for the two samples and four times for the four sample colours. Whenever a prolonged ignition occurred in all of the four tests, the test was then repeated with a lower heat flux until no actual ignition occurred. xiv. The measure results from the above procedures were then noted and recorded accordingly for further analysis. 2.2 Heat Release Rate Determination by Cone Calorimetry ISO 5660 – 1: 2002 2.2.1 Overview In compartment fires the compartment environmental heat flux stemming from the surrounding burning fuel plays a vital role in the growth of fire, the spread of flames and the production of burning products such as ashes. The most vital parameter to be measured in such as case is the heat release rate (HRR) that quantifies the magnitude of the fire. Babrauskas (1992) noted that the heat release rate is the single vital variable that determines the fire hazard performance of potential fire fuel materials. The most commonly used device for measuring the rate of heat release of materials is the cone calorimeter and is now regarded as the most accurate and realistic method for obtaining data in relation to parameters such as the rate of heat release of flames. It is now internationally accredited both for bench-scale and large scale applications. The following procedural steps were followed in the measurements relating to this parameter. 2.2.2 The Test Concept The basis of the test method is that there exists a correlation between the heat released as a result of combustion and the level of oxygen consumed. This principle will be asses in this dissertation. Highly combustible materials that have the aforementioned relationship is represented by an arbitrary value of 13.1 MJ of heat is released per kilogram of oxygen consumed. The experiment would take place in prevailing ventilation measures that could be exposed to pure atmospheric conditions. This was while maintaining the range of thermal radiation to within 100kW/m2. The measurement of the concentrations of oxygen an exhaust fumes were then made according to ISO 5660-1 (2002). The measurement of oxygen concentration after allowing for consumptions were then made. The concentration was dependent on the oxygen concentration and the rate of flow in the product’s combustion stream. 2.2.3 Apparatus used The apparatus that were used consisted include but not limited to; a cone-shaped radiant electrical heater, specimen holders, ignition device, radiation screen, weighing balance for measuring specimen mass, exhaust system, oxygen analyzer, heat flux meter, calibration burner, gas sampling apparatus, a data collection and analysis system. The scheme below shows the setup positions during the testing process. Figure 2.1: Procedural Set-up 2.2.4 Description of Samples The samples tested included pigmented Polymethyl Methacrylate (PMMA) square samples measuring 165 by 165 mm and 5mm thick. The colours I worked with were black, red, green and white. 2.2.5 The Test Procedure i. The cone calorimeter was switched on in readiness for the experiment based on the conditions of the radiant heat source, in this case propane. ii. The calibration of the test was performed. This entailed the determination of the initial status of the heater, oxygen analyser, and heat release. The mass measuring system to be applied and the operating calibrations were also determined. iii. The dimensions of the sample to be tested was then measured. The specimen was then wrapped in a single layer of aluminium foil with the shiny side towards the specimen, covering the unexposed surfaces. This was to prevent it from melting and falling off as that would have contributed to mass loss rate. iv. The sample was then placed in the sample holder, with packing whenever it was required. During the test the sample was held in the appropriate horizontal holder. The heat shield shatter was also placed under the heated cone. v. The sample was then placed on the balance underneath the heated cone. The balance was then tared to eliminate any initial weights. vi. The initial measurements of mass, thickness and sample description were then entered through the data acquisition system. vii. The spark igniter was then placed over the sample. To automatically start the test, the heat shutter was removed. viii. An allowance of 5 seconds passed to ensure the sample had fully ignited. Button 1 was then pressed to show the sample ignited. ix. All the observations were then recorded for further analysis. x. Button 2 was then pressed after all the sample had been consumed. The sample was then removed from the balance. xi. Procedures (iii) to (x) were then repeated for the test that followed. xii. The raw data saved in excel format as obtained from cone test was saved and used in the analysis and drawing of graphs in the next section. 2.3 Smoke Production Rate Whenever the smoke gases from the samples spread quickly, pressure within the compartment increases thus necessitation the ventilation processes. The study of the smoke release rate therefore ensures that accurate rates are arrived at without jeopardizing the entire experiment. In the case of this study, the production of carbon IV oxide, and carbon II oxide was assessed by measuring their concentrations at the vent plane. This was achieved by continuously extracting samples for analysis from the stream of gases that are expelled from the exhaust vent of the cone calorimeter. The location of the samples were then picked in random to ensure consistency. An attempt was made to determine gas concentrations that were representative of the various samples under study. For each sample thereof, soot levels were determined and recorded by the use of light extinction apparatus 3. Test Results and Discussion 3.1 Heat Release Rate The heat release rate is an important fire parameter describing the intensity of the fire, such that a high heat release rate describes a huge fire and vice versa. In accordance with ISO 5660 part 1 (2002), a cone calorimeter was used to study the combustion properties of samples as described herein. The graph of heat release rate (HRR) versus time for the PMMA polymer at a radiance intensity of 25kW/m2 is illustrated in fig. 3.1 below. The curves therein depict the original records as was the output from the cone calorimeter apparatus. It was from these records that parameters such as HRR and total heat release (THR) got derived through the burning of the burning polymer surface. As stated in the previous section, different surface colors of PMMA were tested. To obtain accurate and reliable results, it was paramount that the surface area of the sample tested remand constant throughout the whole experiment. The heat release rate for the black sample is the first to peak and rapidly increases just before 100 s while the red sample doesn’t increase until after 150 s. The black sample attains the highest peak release rate (PHRR) of just above 500 kW/m2 and occurs 300s. On the other hand, the red sample attains the lowest PHRR though earlier than the rest of the sample at 200 s. Subsequently, the HRR for all the four samples decreased rapidly until they became negligible after 700 s. it is important to note that the shape of the HRR curves for all the PMMA samples are similar. The results indicate a significant decrease of 20 percent on the value of PHRR for the various colors with the red sample having the least PHRR. Figure 3.2: Rate of heat release for PMMA samples at intensity of 25kW/m2 The samples were selected so as to be able to easily study the ignitability of the polymer sample with selected properties in relation to polymer decomposition. From fig. 3.1 above therefore, it is evident that the ignition time for the samples moves from the black sample as the first through green and white and lastly red. The red sample depicted melting behavior between 200 s and 300 s. There was a sudden decrease in heat release rate due to the energy being used in the melting process. The heat release rate then increased once more and remained stable for a while before declining again. The samples whose surface did not change during the burning process is depicted by a straight line curve. Figure 3.3: Ideal fire development stages. A comparison of figure 3; the experimental result of the study above and figure 3.2 showing the fire development stages shows that the compartment fire under study is fully developed. It has the growth, flash over and decay portions of development. It is therefore expected that the results and behavioral features of the fire would match with those of a fully developed compartment fire. At an increased intensity of 55kW/m2, the rate of heat release increases much faster than when the radiative intensity is 25kW/m2 as evident from fig. 3.2. The green sample is the first to attain increased heat release rate but also the first to decline, implying that the green sample burns much faster at increase heat intensity. The white sample attains the highest peak heat release rate PHRR. This implies that the white sample is much more risky at high heat fluxes as it burns much faster. The black sample attained peak heat release rate much later compared to other samples at high heat fluxes. This phenomenon can be attributed to the black surface losing much of its heat into the compartment surrounding thus taking time to heat up. The diminishing rate was also much slower compare to other samples. Figure 3.4: Rate of heat release for PMMA samples at intensity of 55kW/m2 From the HRR curves above, it can be said that the rate of heat release can be used as a reliable criteria of ranking that burning behaviors of the various PMMA colors for samples having non-standard sizes. 3.2 Mass loss rate As a technique for the estimation of HRR, the mass loss rate has been advanced greatly due to its ease and minimal measurements requirements. Complete combustion however would lead to heat release rate being over-estimated. The calculated mass loss rates for the various colors of PMMA samples at radiative intensity of 55kW/m2 are plotted in fig. 3.3 below. It is evident that the peak mass loss rate for the black sample is roughly 75% that of the white sample. It is also important to note that the red sample nearly identical to the green sample takes the longest time to lose its mass. There is also evidence of delayed ignition time and heat release rate in the black sample, else the curves are nearly identical for all the samples. Because of a lower mass loss rate, the black sample tend to generate a smaller flame that would in turn reduce the energy feedback rate from the diminished flame to surface of the sample (citation). As a result of this phenomenon, the total heat flux for the black sample in during cone calorimetry was less than that of a white sample as evident in fig. 3.4 below. Figure 3.5: The rate of mass loss vs time It is however generally believed that PMMA samples undergo pyrolysis process that is predominantly a reverse polymerization process (Beyler, 2002). This explains why the white sample exhibits higher mass loss rates but minimal molecular weight loss evidenced by the low heat release rate. This further implies little or no melting of the sample in question. Additionally, for the PMMA polymer chains to decompose and change state, the reverse polymerization process generally requires little amount of heat influx compared to a random pyrolysis process as a result of the unzipping process. In conclusion therefore, the rate of mass loss for the white sample is much greater than other samples, a further evidence that in case of an actual fire, white PMMA polymers do contribute significantly to the build-up and spread of the fire compared to the other samples even at similar heat fluxes. 3.3 Total Heat Release In the measurement of the total heat release, some discrepancies were observed. For the red and black samples, there were no apparent changes when samples were subjected to a radiative intensity of 25kW/m2. This means that the intensity was not sufficient to cause any change in state for that sample. However at a higher intensity of 55kW/m2, the black sample released the highest amount of heat. This can be attributed to the fact that the color black is a good heat absorber and subsequently dissipates heat much faster. Figure 3.6: Total heat release for PMMA samples at 25kW/m2 The red sample had a longer curve of total heat release versus time. This can be attributed to a slow burning rate of the sample compared to other colours. The samples studied have varying thermal stability but unlike polythene that follows a stability pattern, its stability is random. Of the two samples that manage to ignite and release heat, the green sample ignites first but depletes much faster compared to the white sample. Figure 3.7: Total heat release for PMMA samples at 55kW/m2 Figure 3.5 above exemplifies the release of volatile materials during the cone calorimeter heating process. The correlation between time of ignition and total heat release rate is however poor implying that there is no relationship between time of ignition and the total heat release. For the black sample however, the total heat release vs time curve is smooth all the way implying enhanced combustion even at a constant heat flux 3.4 Smoke Production Rate The rate of propagation of smoke as well as its location plays an important role in fire hazard interventions. This experiment aimed at studying the smoke production rate and the results for the various samples are as illustrated in the graph below. The black sample exhibits a high smoke production rate compared to other samples peaking at 2.7l/s just before the 300 s mark. This can be attributed to incomplete combustion as a result of th high heat absorption rate of black materials. The heat is absorbed rapidly hence there is no allowance for complete combustion of the fuel material. The chemical components of the black PMMA sample could also be responsible for the high smoke production rate. The red sample has a deep in smoke production between the 200 s and 300 s mark. As indicated earlier this was attributed to the sample being subject to the melting process at this point. Subsequently, the rate of smoke production for the samples decrease greatly after peaking at 300 s until they were negligible beyond 700 s. Figure 3.8: Smoke release rate at high heat fluxes of 55kW/m2 However, at a higher heat flux of 55kW/m2, the results are significantly different and shown by fig. 3.8 below; Figure 3.9: Rate of smoke release at increased heat flux (55kW/m2) It is evident that in fact the inverse is true as the red sample depicts the highest smoke release rate. The black PMMA sample however portrays a slower decline in the rate compared with the rest of the samples. At high heat fluxes, the rate increases rapidly for the green, red and white samples peaking immediately after the 100 s mark. It implies a higher rate of oxygen consumption therefore predominant incomplete combustion thus the high smoke production rate. The black sample however utilizes its heat absorption property to harness sufficient heat for regulated combustion and moderate oxygen consumption thus the slower rate of smoke production. 4. Conclusion There is an apparent correlation between total heat released and the amount of oxygen consumed during the combustion process of compartment fires. It therefore means that the importance of the properties of the initial surface (obtained through test calibration) cannot be overlooked since it has a significant bearing on the results of the heat release rate. It was concluded therefore that the flame holding surface accounts for only 80% percent of its original value. The heat release rate (HRR) of a sample especially samples with arbitrary dimensions cannot be used as a reliable parameter in trying to predict the burning behavior of the samples. It is only in standardized samples that forecasts can be made regarding the possible results of a burning process involving similar material in an actual fire. Rather, the rate of oxygen consumption would offer a more accurate approximation. Black PMMA polymer material have a higher heat release rate compared to similar materials of different colour. As explained earlier, the heat conductivity of the material depends on its chemical composition and physical properties such as color, and black is a good heat absorber and dissipater. Fully developed compartment fires are easily achieved using black PMMA materials when subjected to low heat fluxes and the same applies for white polymer materials when subjected to high heat fluxes. There is a correlation between the rate of smoke production and the intensity of burning. However, there is no correlation between the smoke production rate and the thermal stability of the polymers. This can be further assessed by means of non-isothermal thermo-gravimetry. This however does not apply to all the polymers as some show signs of correlation. 5. References Babrauskas, V. and Peacock, R.D., 1992. Heat release rate: the single most important variable in fire hazard. Fire safety journal, 18(3), pp.255-272 Babrauskas, V., 1984. Development of the cone calorimeter—a bench‐scale heat release rate apparatus based on oxygen consumption. Fire and Materials, 8(2), pp.81-95. Beyler, C.L. and Hirschler, M.M., 2002. Thermal decomposition of polymers. SFPE handbook of fire protection engineering, 2, pp.110-131. Bullen, M.L. and Thomas, P.H., 1979, January. Compartment fires with non-cellulosic fuels. In Symposium (International) on Combustion (Vol. 17, No. 1, pp. 1139-1148). Elsevier. Chow, W.K., 1996. Simulation of tunnel fires using a zone model. Tunnelling and Underground Space Technology, 11(2), pp.221-236. Fleischmann, C.M. and Parkes, A.R., 1997. Effects of ventilation on the compartment enhanced mass loss rate. Fire Safety Science, 5, pp.415-426. Gilman, J.W., 1999. Flammability and thermal stability studies of polymer layered-silicate (clay) nanocomposites. Applied Clay Science, 15(1), pp.31-49. Kumar, R. and Naveen, M., 2007. Compartment fires: CALTREE and cross-ventilation. Combustion Science and Technology, 179(8), pp.1549-1567. Pierce, J.B.M. and Moss, J.B., 2007. Smoke production, radiation heat transfer and fire growth in a liquid-fuelled compartment fire. Fire safety journal, 42(4), pp.310-320. Quintiere, J.G., 1981. An approach to modeling wall fire spread in a room. Fire Safety Journal, 3(4), pp.201-214. Thomas, P.H. and Heselden, A.J.M., 1972. Fully-developed firess in single compartments: A co-operative research programme of the Conseil International du Bâtiment (CIB report no. 20) Fire Research Station Fire Research Note 923. Building Research Establishment, Borehamwood. Utiskul, Y., 2006. Theoretical and experimental study on fully-developed compartment fires. Read More

Babrauskas (1992) noted that the heat release rate is the single vital variable that determines the fire hazard performance of potential fire fuel materials. The most commonly used device for measuring the rate of heat release of materials is the cone calorimeter and is now regarded as the most accurate and realistic method for obtaining data in relation to parameters such as the rate of heat release of flames. It is now internationally accredited both for bench-scale and large scale applications.

The following procedural steps were followed in the measurements relating to this parameter. 2.2.2 The Test Concept The basis of the test method is that there exists a correlation between the heat released as a result of combustion and the level of oxygen consumed. This principle will be asses in this dissertation. Highly combustible materials that have the aforementioned relationship is represented by an arbitrary value of 13.1 MJ of heat is released per kilogram of oxygen consumed. The experiment would take place in prevailing ventilation measures that could be exposed to pure atmospheric conditions.

This was while maintaining the range of thermal radiation to within 100kW/m2. The measurement of the concentrations of oxygen an exhaust fumes were then made according to ISO 5660-1 (2002). The measurement of oxygen concentration after allowing for consumptions were then made. The concentration was dependent on the oxygen concentration and the rate of flow in the product’s combustion stream. 2.2.3 Apparatus used The apparatus that were used consisted include but not limited to; a cone-shaped radiant electrical heater, specimen holders, ignition device, radiation screen, weighing balance for measuring specimen mass, exhaust system, oxygen analyzer, heat flux meter, calibration burner, gas sampling apparatus, a data collection and analysis system.

The scheme below shows the setup positions during the testing process. Figure 2.1: Procedural Set-up 2.2.4 Description of Samples The samples tested included pigmented Polymethyl Methacrylate (PMMA) square samples measuring 165 by 165 mm and 5mm thick. The colours I worked with were black, red, green and white. 2.2.5 The Test Procedure i. The cone calorimeter was switched on in readiness for the experiment based on the conditions of the radiant heat source, in this case propane. ii. The calibration of the test was performed.

This entailed the determination of the initial status of the heater, oxygen analyser, and heat release. The mass measuring system to be applied and the operating calibrations were also determined. iii. The dimensions of the sample to be tested was then measured. The specimen was then wrapped in a single layer of aluminium foil with the shiny side towards the specimen, covering the unexposed surfaces. This was to prevent it from melting and falling off as that would have contributed to mass loss rate. iv. The sample was then placed in the sample holder, with packing whenever it was required.

During the test the sample was held in the appropriate horizontal holder. The heat shield shatter was also placed under the heated cone. v. The sample was then placed on the balance underneath the heated cone. The balance was then tared to eliminate any initial weights. vi. The initial measurements of mass, thickness and sample description were then entered through the data acquisition system. vii. The spark igniter was then placed over the sample. To automatically start the test, the heat shutter was removed. viii. An allowance of 5 seconds passed to ensure the sample had fully ignited.

Button 1 was then pressed to show the sample ignited. ix. All the observations were then recorded for further analysis. x. Button 2 was then pressed after all the sample had been consumed. The sample was then removed from the balance. xi. Procedures (iii) to (x) were then repeated for the test that followed. xii. The raw data saved in excel format as obtained from cone test was saved and used in the analysis and drawing of graphs in the next section. 2.

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