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.solve please question 3 in details
.solve please question 3 in details
Semester One Final Examinations, 2021 FIRE3700/FIRE7600 Introduction to Fire Safety Engineering Question 3. (20 points) An ionising smoke detector is set to sound an alarm if its output is less than 70pA. Smoke blocks light and the drop in intensity of light across a control volume is described by the Lambert-Beer law: 1₂ = loexp(-KCL) where lo is the incident light source and I, the light that is capable of traversing a distance L (m), C is the soot concentration (dimensionless), and x is the light extinction coefficient which is a constant dependent on the nature of the soot produced by a burning fuel. Typical values for the output transmission as a function of output pA is shown in Figure 3. 16.7 12.9 60 9.7 70 6.9 121 0 90 80 70 60 50 40 $2269 MEASURING IONIZATION CHAMBER OUTPUT-PICOAMPERES Figure 3. Percentage light transmission and percent obscuration per foot as a function of output-pico Amperes (pA) of an ionising smoke detector. Note: 3.28 feet = 1 m. a) What is the allowable sensitivity of the detector in % light transmitted? (5 points) A 150 kW fire develops in a 4 m wide, 20 m long, and 3 m tall corridor. Smoke detectors as per the one above are placed as a single row in the corridor, spaced every 4 m. The concentration of smoke in the corridor has been modelled resulting in Figure 4 below. Page 5 of 8 Semester One Final Examinations, 2021 FIRE3700/FIRE7600 Introduction to Fire Safety Engineering 120 100 80 60 0 4 5 Time [minutes] Figure 4. Smoke concentration in the corridor. b) Show whether or not the smoke detectors will activate early enough to ensure a safe egress from the corridor. Assume that: the smoke detector is calibrated based on a light extinction coefficient of x = 1.5, and over a length of 1 m; and . people would be disabled when 90 % of the light from the exit sign is blocked. (10 points) c) Because of the specific fire hazard, the type of fire expected to occur in the corridor is a smouldering fire. What type of smoke detector would you recommend to use, ionisation or photoelectric? (5 points) 90 100 100 Concentration [%] 40 20 0
Semester One Final Examinations, 2021 FIRE3700/FIRE7600 Introduction to Fire Safety Engineering Question 3. (20 points) An ionising smoke detector is set to sound an alarm if its output is less than 70pA. Smoke blocks light and the drop in intensity of light across a control volume is described by the Lambert-Beer law: 1₂ = loexp(-KCL) where lo is the incident light source and I, the light that is capable of traversing a distance L (m), C is the soot concentration (dimensionless), and x is the light extinction coefficient which is a constant dependent on the nature of the soot produced by a burning fuel. Typical values for the output transmission as a function of output pA is shown in Figure 3. 16.7 12.9 60 9.7 70 6.9 121 0 90 80 70 60 50 40 $2269 MEASURING IONIZATION CHAMBER OUTPUT-PICOAMPERES Figure 3. Percentage light transmission and percent obscuration per foot as a function of output-pico Amperes (pA) of an ionising smoke detector. Note: 3.28 feet = 1 m. a) What is the allowable sensitivity of the detector in % light transmitted? (5 points) A 150 kW fire develops in a 4 m wide, 20 m long, and 3 m tall corridor. Smoke detectors as per the one above are placed as a single row in the corridor, spaced every 4 m. The concentration of smoke in the corridor has been modelled resulting in Figure 4 below. Page 5 of 8 Semester One Final Examinations, 2021 FIRE3700/FIRE7600 Introduction to Fire Safety Engineering 120 100 80 60 0 4 5 Time [minutes] Figure 4. Smoke concentration in the corridor. b) Show whether or not the smoke detectors will activate early enough to ensure a safe egress from the corridor. Assume that: the smoke detector is calibrated based on a light extinction coefficient of x = 1.5, and over a length of 1 m; and . people would be disabled when 90 % of the light from the exit sign is blocked. (10 points) c) Because of the specific fire hazard, the type of fire expected to occur in the corridor is a smouldering fire. What type of smoke detector would you recommend to use, ionisation or photoelectric? (5 points) 90 100 100 Concentration [%] 40 20 0