Small-Scale Compartment Fire Experiments - Report Example

University of Central Lancashire School of Forensic and Investigative Science FV1202 Engineering Design Practice Laboratory: Small-scale compartment fire experiments Introduction The performance of the experiment is to help in understanding of compartment fires with the information involved being both descriptive and scientific. The objective of the experiment is to perform an assessment on the development of fire from the time of ignition, through flashover to decay. A compartment fire is fire is a fire which is enclosed in a space which maybe fuel controlled or ventilation controlled (ventilation limited). In the fuel controlled fire there is sufficient air to enable complete reaction of the fuel with air in the enclosure while for the ventilation control there is no sufficient air for complete reaction of the fuel. Compartment fires go through various stages including ignition, growth, flashover, fully developed and the decay stages. At the early stages of the fire the compartment has a negligible effect on the fire development. As the growth of fire continues the smoke and hot gases generated forms a layer below the ceiling and this results into the gases flowing out of the compartment. Suppose the growth of fire continues with the opening being to small to be able to carry out the products of combustion at the same rate of production, the upper layer increases to starts moving towards the floor. The fire may further develop leading to occurrence of flashover and this means the compartment will be fully involved. After the consumption of fuel in compartment the fire starts decaying and it extinguishes itself as there is no more fuel to be involved in combustion. Description of Experimental Equipment Fire Box The fire box is a small-scale compartment that has a nominal inside dimensions of (0.65m long by 0.34m wide by 0.38m high). The thickness of the roof, walls and floor construction are about 0.025m in thickness with and external layer of monolus 500 lining where 1 wall construction is by fire resistant glass. The fire box has a door whose opening can be adjusted with a height of 225mm and the opening option ranges from 0 to 0.15m width. A hole is incorporated in the floor through which there is an axle that passes whose function is to support the fuel and it rests on a balance below, thus the weight of the material can be recorded. it is positioning is such that its centre is about 0.45m from the opening. The fire box is fixed inside a steel frame that has wheels which facilitate easy movement. The rear wall has three columns of four thermocouples and there is another thermocouple which protrudes through the floor hole with the distribution of the thermocouples being as shown in the figure below. Thermocouples A total of thirteen thermocouples are utilized in measuring the temperatures in the course of the experiment. These are the types referred to as type K (nickel - chromium / nickel - aluminium) which have stainless steel sheet. A total of twelve thermocouples are used in measurement of the inside air temperature at the rear wall of the compartment while one thermocouple protrudes through the floor hole. The projection of the thermocouples is about 200mm into the firebox, as illustrated in figure 1 and there positioning is in three columns at distances of 0.15m, 0.315m and 0.48m from the opening and are also connected to the a Squirrel data logger to enable recording of the temperatures in the compartment during the experiment. Figure 1 –Side view of fire box with thermocouples showing nominal measurements Figure 2 –Fire box front view, full sized opening showing nominal measurements Figure 3 – Fire box front view half opening showing nominal measurements Experimental Materials: Fuel (PMMA) The materials used in this experiment were square slabs of PMMA (Polymethyl Methacrylate) which were burnt in the small scale fire compartment. PMMA find wide application in small-scale compartment where a single sample is burned for each test performed. A fuel thickness of about 0.012m (12mm) or 0.25m (25mm) with a measurement of about 100mm by 100mm or 150mm by 150mm or 200mm by 200mm is normally used. Experimental Procedure The experiment followed the following procedure. First all the internal dimensions of the fire box were taken and also the point to locate the sample was located in the fire box. The ventilation size was located, all the thermocouples inside the firebox were cleaned using a towel so that to ensure the reading that were to be made were not affected by dirt of soot. The thermocouples were then connected to squirrel data logger with a record of which thermocouple that was linked to specific channels being made. The balance was switched on with an appropriate size sample tray being placed on support plate in the fire box before the “tare” key on the balance was pressed. All the samples were added to the tray with some fine PMMA powder being added on the fuel sample. The initial mass of fuel PMMA was recorded and all the thermocouples were straightened so that they could protrude horizontally into the firebox. A marked measuring stick was placed into the firebox (near to the front door as to make it more visible) so as to allow the observation of smoke height at some time intervals. After starting the squirrel data logger the sample was ignited by use of a lit paper (appropriate PPE use was necessary to ensure no injuries could be encountered during the experiment. The vent opening was then adjusted to appropriate size during the experiment. A small paper was placed at the front of the box so that observation of signs of flashover during the experiment could be made with the time at which flashover occurred being recorded. The mass of the sample was recorded as well as the height of the smoke layer for every minute with any other important also being recorded. At about 15 minutes after ignition for the experiments a record was made for suitable condition for black draught condition occurrence. When tests were completed the data logger was stopped. Requirements of experiment The following four experiments will be carried using the procedures described earlier. The first experiment was carried out with the compartment being subjected to cold conditions and the compartment being fully open The second procedure involved full opening of compartment in a warm experimental procedure The third experiment involved half size opening of compartment in a cold experimental procedure The fourth was in warm experimental procedure with half size opening of the window. Results First test The first test involved full ventilation with cold compartment. The fuel was all over the surface at for in the first minute and in the second minute the fuel was concentrated at the middle. In the third minute fire was seen to start on the hard part. In the sixth minute the fire was developed on the fuel with a sizzling sound being hard. The eighth minute of the fire so the fire rise. In the tenth minute an increase in the fire flame size was seen. At 14 minute some liquid fuel was identified on the surface. At the seventh minute a temperature of 320 degree was recorded. At 19 minutes to 21 minutes a paper which was placed around the door smoked an indication of flashover. At 23 minutes there was a lazy backdraft of the fire and in the 24th minute the fire died down with the mass recoding of the tray having reduced from the initial 1833.6mg to 1529.4 mg. The result of time with respective change in mass is as shown in table 1 and figure 4. Table 1 Time Mass of fuel tray Change in mass 1 1833.6 0 2 1831.0 2.6 3 1827 6.6 4 1825 8.6 5 1829.4 4.2 6 1823.4 10.2 7 1824.0 9.6 8 1822.6 11 9 1819.4 14.2 10 1816 17.6 24 1529.4 304.2 Figure 4 Second test In the second test there was half ventilation with fire coming bigger at the middle of the surface in the third minute. The fire level raised in fourth minute with the whole surface getting fire in the fifth minute. In the sixth minute the ceiling of the compartment was reached by the fire and liquid was seen on the surface of the fuel. In the tenth minute paper started smoking with the eleventh minute witnessing the complete burning on the surface of fuel. In the sixteenth minute there was complete burning of the paper and the door was closed in the seventeenth minute the door was also closed and there was no flashover. In the eighteenth minute flashover occurred with the door being closed. In the nineteenth minute gases wee seen to go under sample holder. In the twenty second minute there was flashover. The door was closed at 24.18 and open at 24.28 with flash over occurring but fire was only near the door. At 25.30, fire was retreating back in the surface at the fire died down at 26.36, with mass having reduced from 1803.2 to 1355.8. The change of mass with time is as given in table 2 and figure 5. Table 2 Time in minutes Mass Change in mass 0 1803.2 0 1 1796.6 6.6 2 1793.3 9.9 3 1789.0 14.2 4 1783.2 20.0 5 1775.4 27.8 6 1766.2 37.0 7 1751.8 51.4 8 1735.8 67.4 9 1714.7 88.5 10 1699.3 103.9 11 1682.0 121.2 12 1657.2 146 13 1630.2 173 14 1610.8 192.4 15 1589.2 214 16 1567.7 235.5 17 1547.3 255.9 18 1524.2 279 19 1508.2 295 20 1465.0 338.2 21 1444.0 359.2 22 1434.2 369 23 1417.3 385.9 24 1393.6 409.6 25 1370.8 432.4 26 1355.8 447.4 Figure 5 Third test The third test involved half ventilation in warm surface where at 0.40 level of fire was noticed to rise and at 1.00 whole surface of the material was on fire. At three the paper started smoking at 4.00 the paper started burning and at 5.00 the whole paper burned. At 7.00 the door was closed and there was only smoke with no flash over. There was a small flashover fire at 8.10 where fire was only under the surface. At 10.00 there was no flashover and the door was closed. At 11.00 fire was near the door. At 12.00 the largest flashover was noticed also at 13.00 with fire being noticed near the door. Flashover proceeded up to 14.00 and the fire died at 15.30. The test experienced fuel mass reducing from 597.6 to 376.2 at 15.30 when the fire died. The result of time with respective change in mass is as shown in table 3 and figure 6. Table 3 Time in minutes Mass of fuel 0 597.6 0 1 589.4 8.2 2 581.4 16.2 3 563.4 34.2 4 545.8 51.8 5 523.6 74 6 503.6 94 7 481.5 116.1 8 463.8 133.8 9 436.8 160.8 10 399.2 198.4 11 402.1 195.5 12 333.0 264.6 13 391.0 206.6 14 349.0 248.6 15 376 221.6 Figure 6 Fourth test This test involved full ventilation in a warm experimental procedure. In the third minute the fire got to all the surfaces with the paper releasing smoke. At 3.10 the paper was on fire and at 5.20 the door was close and was opened at 5.20 and a flashover was seen. At time 7.40 there was a flashover with another flashover at 9.15. At 9.55 the door was closed for 10 seconds and no flashover was experienced and finally the fire died at 11.20. In the process of this experiment the mass of fuel changed from 1548.2 in the first minute to 1266.6 at 10.51. The result of time with respective change in mass is as shown in table 4 and figure 4. Table 4 Time Mass of fuel Change in mass 1 1548.2 0 2 1582.6 -34.4 3 1556.3 -8.1 4 1542.1 6.1 5 1514.2 34 6 1551.7 -3.5 7 1426.2 122 8 1532.6 15.6 9 1474.0 74.2 10 1431 117.2 11 1266 282.2 Figure 7 Discussion From the graph it could be seen that there was a general trend of the mass reducing with time but in some incidences the mass appear to rise before dropping again. The increase in mass could be attributed with development of pressure within the chamber. On the other hand the general trend where there was a reduction in mass could be attributed to the fuel being turned into gaseous products which escaped through the door. The behavior of the fire in this experiment is useful in prediction the behavior of fire in real life situation. The fire fighter need to know the point where flash over may occurring when an incident of fire occurs. This will help in ensuring that all safety measures are taken at that point. Read More