Fire Box Experiment - Lab Report Example

AIM OF THE EXPERIMENT The main Objective of this experiment was to study the different stages of fire development. How parameters like temperature and the consumption of the combustible material (fuel) vary during the various stages. This was achieved by burning 10cm of Polymethyl methacrylate (PMMA) in the first experiment and 20 cm of PMMA in the second experiment. The experiments were conducted in a controlled fire box complete with all components of the fire triangle. APPARATUS USED FIREBOX This is a specialized compartment for holding controlled fire experiments in a typical laboratory. Its dimensions are 0.65m length by 0.34 m width by 0.38m height. The interior walls, roof and floor are made of 0.025m thick a non-combustible material Monolux 500. One wall is made of hard fire-resistant glass which enables one to view actions happening inside the firebox during the experiment safely. To let in oxygen, the firebox has a ventilation measuring 0.23m high by 0.155 m wide. The firebox rests on a steel frame to guarantee easy movement. THERMOCOUPLES On the rear wall, a dozen thermocouples arranged in three columns of four thermocouples each were used to take the air temperature inside the firebox. The fuel is placed on a stainless steel tray which is supported by an axle passing through a tight hole drilled on the floor of the box. The weight of the fuel was measured using an electronic scale throughout the experiment. The diagram below illustrates the above set-up. METHODOLOGY PMMA was greased with petroleum gel for fast ignition. Some grounded PMMA was sprinkled on the fuel to hasten the ignition too. The fuel was kept on the tray at a distance of 130mm from the ventilation window. Change in mass was recorded by an electronic scale. Temperature was recorded using the Squirrel data logger connected to the thermocouples before and during the experiment. The onset of the experiment was marked by setting the fuel on fire which was done using a torch. The experiment was conducted with first 10 cm and 20 cm of fuel respectively. MEASUREMENTS AND ACCURACY The measuring equipment’s used were advanced and can be found in any modern University laboratory. The devices guaranteed accuracy, safety to the users and are eco-friendly thus not putting the students or the environment in any possible direct or indirect risk. The variables measured during the measurements are; 1- Fuel Measurements (PMMA) initial and gradual weight loss with respect to time was measured using an electronic scale which has a 0.01g accuracy 2- Air temperature inside the firebox was measured using Squirrel data logger right from the room temperature, ignition stage, growth fully developed and the decay stages of the fire. Other observations were visual e.g. smoke production rate and pattern throughout the experiment. Flame vigour and its spread till it became extinguished during the decay stage. DATA OBTAINED 1. THE CHANGING MASS OF PMMA DURING THE EXPERIMENT The mass of the PMMA which was initially at 250 grams was recorded throughout all the stages of the fire. The readings were recorded every 30 seconds as shown in the table below. Mass (g) EXP 1 250 250 250 250 250 249 249 249 248 Mass (g) EXP 2 253 253 253 252 252 251 250 250 248 Time (Seconds) 0 30 60 90 120 150 180 210 240 Mass (g) EXP1 248 247 247 246 246 245 244 243 243 Mass (g) EXP 2 247 246 244 242 240 236 233 229 224 Time (Seconds) 270 300 330 360 390 420 450 480 510 Mass (g) EXP 1 242 241 240 239 237 236 234 233 231 Mass (g) EXP 2 221 216 211 205 199 193 186 181 174 Time (Seconds) 540 570 600 630 660 690 720 750 780 Mass (g) EXP 1 229 228 225 223 221 218 216 214 211 Mass (g) EXP 2 167 161 155 148 142 135 130 123 116 Time (Seconds) 810 840 870 900 930 960 990 1020 1050 Mass (g) EXP 1 208 205 203 199 196 192 189 185 181 Mass (g) EXP 2 112 103 95 90 83 76 68 61 52 Time(Seconds) 1080 1110 1140 1170 1200 1230 1260 1290 1320 Mass (g) EXP 1 177 173 169 164 159 154 `148 143 138 Mass (g) EXP 2 45 39 33 27 19 13 7 4 Time(Seconds) 1350 1380 1410 1440 1470 1500 1530 1560 1590 Mass (g) EXP 1 132 126 120 113 106 102 97 92 86 Time(Seconds) 1620 1650 1680 1710 1740 1770 1800 1830 1860 Mass (g) EXP 1 80 74 67 62 56 51 46 42 36 Time(Seconds) 1890 1920 1950 1980 2010 2040 2070 2100 2130 Mass (g) EXP 1 31 27 23 18 14 11 8 7 5 Time(Seconds) 2160 2190 2220 2250 2280 2310 2340 2370 2400 Mass (g) EXP 1 4 4 3 3 3 3 3 ` Time(Seconds) 2430 2460 2490 2520 2550 2580 2610 2. TEMPERATURE RECORDED DURING THE EXPERIMENT The objects above contain the temperature readings recorded by the thermocouples. The data was large and given the maximum number of pages allowable, it couldn’t fit. Clicking on the objects opens the spreadsheets containing the data. Below is the graph below from the data and the analysis. TIMELINE OF THE FIRE AND CORRESPONDING OBSERVATION Incipient Stage Time (s) Observation 0-15 PMMA is set on fire and starts burning 16-199 Smoke being released is now observable because its dark in colour 200-460 The flame which is orange in colour grows in size, Some rumbling sound is heard indicating the spread of the fire Growth Stage 461-660 The flame glows brightly and less smoke is now available. Two thirds of the fuel tray is on fire Fully Developed Stage 670-1100 The flame is vigorous and increases even in height. The fuel bed is fully on fire and even the tray is engulfed. A lot of smoke and hot gases look for escape out of the ventilations Decay Stage 1860-2010 The flame starts to decrease in size. Less smoke is now generated. 2600 The fire extinguishers itself. the fuel is now wholly consumed EXPLANATION AND ANALYSIS OF THE DATA TEMPERATURE VARIATION IN THE FIREBOX EXPLAINED Six thermocouples are placed under the tray holding the fuel inside the box. This set of thermocouples record a similar temperature range. However, thermocouple 1 records the lowest temperature because of its location. At the lowest corner of the box. Thermocouple 9 comes second in recording the second lowest temperature. This is as a result of it being situated near the bottom of the ventilation door. This is the entry point of fresh cool air into the box hence lower temperatures. Thermocouple 6 was nearest to the fire bed and recorded abrupt sharp temperature changes due to flame impingement. Thermocouple 4 which was at the top corner showed the highest temperature attributed to smoke and hot gases being dispersed in that area fast. The other 6 thermocouples located at the top of the box records the highest temperatures. A smoky thermal layer was generated at this zone. Thermocouple 7 and 8 showed the highest temperatures due to their close location to the fire. The spikes observed in the graph could be due to impingement on the thermocouples. Since the mass of hot air flows out of the vent, this explains the high temperatures recorded by thermocouple 12. 750 was the highest temperature reached by the 20cm fuel and 285 for the 10 cm. Temperatures from the higher volume mass of fuel burnt were generally higher than the lesser volume. MASS LOSS EXPLAINED In the initial fire development stage of ignition, the mass remains significantly stagnant. This is because the fire was at its initial stages and minimal amounts of the fuel was burning in both cases. In the growing phase, mass loss is high and the rate of heat being released is rampant too. During the fully developed fire stage, the highest mass loss is witnessed as the fire is at its peak in burning and consuming the fuel. The heat released is used to sustain the fire in its spread. In decay stage, the mass consumption of the fuel margins begins to drop in a constant rate in both experiments. Graphically, it can be shown that the heat released is directly proportional to the mass loss rate. EVALUATION OF THE EXPERIMENT The experiment vividly showcased the four stages of fire which are inception, developing/growing, fully developed and decay stage. The characteristics and behaviour which fires exhibit regarding fuel consumption and temperatures were also clearly studied during the experiment. The results of the experiment are highly applicable in compartment fires in today’s buildings. Low temperature, low mass loss and low heat release are the three major indicators that a fire is in the ignition stages. A relative increase of the above parameters is witnessed in the developing fire stage. In the fully developed stage, temperatures, mass loss and heat release are at their epitome. Finally, all the three parameters show a decline as a result of a dying fire. The temperature of the upper layers of the gas did not meet the threshold of 600 degrees Celsius for the flashover to take place. The size of the fuel could have been a contributing factor. It was small in size thus unable to give off enough energy required for a flashover. For excellent results the apparatus must be accurately and readings carefully taken. Safety when it comes to fires is highly paramount and following instructions is key for successful experiments. The experiment was successful and objectives met as the critical aspects of combustion, heat transfer and fire analysis were thoroughly covered. REFERENCES Babrauskas, V. and Grayson, S. (2009). Heat release in fires. 1st ed. [Place of publication not identified]: Interscience communications. Field, A. and Hole, G. (2012). How to design and report experiments. 1st ed. Los Angeles: SAGE. Karlsson, B. and Quintiere, J. (2000). Enclosure fire dynamics. 1st ed. Boca Raton, FL: CRC Press. Wickström, U. (1979). Temperature analysis of compartment fires and fire-exposed structures. 1st ed. Read More

Mass (g) EXP 1 250 250 250 250 250 249 249 249 248 Mass (g) EXP 2 253 253 253 252 252 251 250 250 248 Time (Seconds) 0 30 60 90 120 150 180 210 240 Mass (g) EXP1 248 247 247 246 246 245 244 243 243 Mass (g) EXP 2 247 246 244 242 240 236 233 229 224 Time (Seconds) 270 300 330 360 390 420 450 480 510 Mass (g) EXP 1 242 241 240 239 237 236 234 233 231 Mass (g) EXP 2 221 216 211 205 199 193 186 181 174 Time (Seconds) 540 570 600 630 660 690 720 750 780 Mass (g) EXP 1 229 228 225 223 221 218 216 214 211 Mass (g) EXP 2 167 161 155 148 142 135 130 123 116 Time (Seconds) 810 840 870 900 930 960 990 1020 1050 Mass (g) EXP 1 208 205 203 199 196 192 189 185 181 Mass (g) EXP 2 112 103 95 90 83 76 68 61 52 Time(Seconds) 1080 1110 1140 1170 1200 1230 1260 1290 1320 Mass (g) EXP 1 177 173 169 164 159 154 `148 143 138 Mass (g) EXP 2 45 39 33 27 19 13 7 4 Time(Seconds) 1350 1380 1410 1440 1470 1500 1530 1560 1590 Mass (g) EXP 1 132 126 120 113 106 102 97 92 86 Time(Seconds) 1620 1650 1680 1710 1740 1770 1800 1830 1860 Mass (g) EXP 1 80 74 67 62 56 51 46 42 36 Time(Seconds) 1890 1920 1950 1980 2010 2040 2070 2100 2130 Mass (g) EXP 1 31 27 23 18 14 11 8 7 5 Time(Seconds) 2160 2190 2220 2250 2280 2310 2340 2370 2400 Mass (g) EXP 1 4 4 3 3 3 3 3 ` Time(Seconds) 2430 2460 2490 2520 2550 2580 2610 2.

TEMPERATURE RECORDED DURING THE EXPERIMENT The objects above contain the temperature readings recorded by the thermocouples. The data was large and given the maximum number of pages allowable, it couldn’t fit. Clicking on the objects opens the spreadsheets containing the data. Below is the graph below from the data and the analysis. TIMELINE OF THE FIRE AND CORRESPONDING OBSERVATION Incipient Stage Time (s) Observation 0-15 PMMA is set on fire and starts burning 16-199 Smoke being released is now observable because its dark in colour 200-460 The flame which is orange in colour grows in size, Some rumbling sound is heard indicating the spread of the fire Growth Stage 461-660 The flame glows brightly and less smoke is now available.

Two thirds of the fuel tray is on fire Fully Developed Stage 670-1100 The flame is vigorous and increases even in height. The fuel bed is fully on fire and even the tray is engulfed. A lot of smoke and hot gases look for escape out of the ventilations Decay Stage 1860-2010 The flame starts to decrease in size. Less smoke is now generated. 2600 The fire extinguishers itself. the fuel is now wholly consumed EXPLANATION AND ANALYSIS OF THE DATA TEMPERATURE VARIATION IN THE FIREBOX EXPLAINED Six thermocouples are placed under the tray holding the fuel inside the box.

This set of thermocouples record a similar temperature range. However, thermocouple 1 records the lowest temperature because of its location. At the lowest corner of the box. Thermocouple 9 comes second in recording the second lowest temperature. This is as a result of it being situated near the bottom of the ventilation door. This is the entry point of fresh cool air into the box hence lower temperatures. Thermocouple 6 was nearest to the fire bed and recorded abrupt sharp temperature changes due to flame impingement.

Thermocouple 4 which was at the top corner showed the highest temperature attributed to smoke and hot gases being dispersed in that area fast. The other 6 thermocouples located at the top of the box records the highest temperatures. A smoky thermal layer was generated at this zone. Thermocouple 7 and 8 showed the highest temperatures due to their close location to the fire. The spikes observed in the graph could be due to impingement on the thermocouples. Since the mass of hot air flows out of the vent, this explains the high temperatures recorded by thermocouple 12.

750 was the highest temperature reached by the 20cm fuel and 285 for the 10 cm. Temperatures from the higher volume mass of fuel burnt were generally higher than the lesser volume. MASS LOSS EXPLAINED In the initial fire development stage of ignition, the mass remains significantly stagnant.

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