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Semester One Final Examinations, 2019 FIRE3700/7600 Introduction to Fire Safety Engineering QUESTION 2. (35 points) A fire develops in a compartment of dimensions 5 m (width), 5 m (length), and 3 m (height) with a door of dimensions 1 m (width) and 2 m (height). A hollow-core steel beam (Figure 4) is placed within the compartment. The steel has the following thermal properties: Thermal conductivity: k = 38 W.m-¹.K-¹ Density: p = 8,500 kg.m-3 Specific heat capacity: cp = 1,000 J.kg-¹.K-¹ a) Using the Thomas plot (Temperature - Opening factor) shown in Figure 3 below, determine the temperature in the compartment after flashover. (15 points) Symbol Shape Solid points 0 121 221 A are means of 8-12 tests 0 211 441 40 20 620 0 1000- 040 20 40 940 80/30 mean values Ⓒ40 2020 o 010 2,1 fuel 8 200 10 20 30 40 AT/AoHo 1/2 (m-1/2) Figure 3. Thomas plot that correlates temperature and the inverse opening factor. AT excludes the area of the opening and the floor. Ao is the area of the opening and Ho is the height of the opening. b) At the instant the compartment reaches flashover, the beam has reached 100°C. Determine the time from flashover until the beam reaches a critical temperature of 500°C (20 points). It can be assumed that the total heat transfer coefficient between the fire and the beam is h = 50 W.m-2. K-1, and there are no heat losses at the interior of the hollow-core beam. 2 mm 50 mm Figure 4. Hollow-core steel beam. Tgas (°C) 500 400 204 +20 50 mm 0 D 0₂0 I