SCALE MODELING RESULTS ON SMOKE SPREADING ......International Journal on Engineering Performance-Based Fire Codes, Volume 8, Number 4, p.145-151, 2006 145 SCALE MODELING RESULTS ON

International Journal on Engineering Performance-Based Fire Codes, Volume 8, Number 4, p.145-151, 2006

145

SCALE MODELING RESULTS ON SMOKE SPREADING AND CONTROL IN A DOUBLE-DECK BUS W.K. Chow, K.C. Lam and N.K. Fong Research Centre for Fire Engineering, Area of Strength: Fire Safety Engineering The Hong Kong Polytechnic University, Hong Kong, China H. Dong, G.W. Zou and Y. Gao Department of Building Engineering, Harbin Engineering University, Harbin, Heilongjiang, China (Received 2 August 2006; Accepted 9 October 2006) ABSTRACT With so many bus fires happened in the past years, a series of investigational works were carried out. This paper is on reporting the results on smoke movement by scale modeling technique. A 1/10 scale double-deck bus model was constructed. A pool fire was placed at different positions of the lower deck of the bus model. Smoke spreading from the lower deck to the upper deck was observed. Air temperature profiles in the two decks were measured. Further, performance of two smoke control schemes with natural vents was evaluated. By opening a ceiling vent or the rear window, smoke can be removed. The smoke temperature in the upper deck is reduced. 1. INTRODUCTION There were many accidental fires in double-deck buses in Hong Kong and Mainland in the past few years [1-5]. Flashover occurred rapidly with all combustibles including wall, floor, ceiling, glazing and furniture burnt up within 15 minutes. Only the steel engine chassis was left behind. The topic was raised again in July 2006 [5]. As suggested by Chow [5] in an interview based on earlier studies [6-11] on double-deck bus fires with fire models, smoke control, at least in the upper deck, should be considered. Removing hot smoke would extend the time to flashover. More time is then available for safe evacuation. A long-term project on double-deck bus fire was worked out. Mathematical modeling on simulating smoke spread was reported. Studying indoor aerodynamics induced by a fire in a scale model is the second stage. Surface spread of flame over the walls, ceiling and glazing materials, ignition of other furniture items, flashover, smoke toxicity, and fire endurance would then be studied later [12-15]. A 1/10 scale model for a typical double-deck bus with the same configurations used earlier [8] for CFD simulations was constructed in a remote area of Northeast China. Different fire scenarios were identified and set up. Transient smoke spreading, temperature variations and flow characteristics were studied. Two different natural smoke exhaust schemes by opening the ceiling window or the rear window on the upper deck were considered. The

measured fire environment for those scenarios will be reported in this paper first. 2. THE SCALE MODEL A 1/10 scale model was constructed for a typical local double-deck bus. Such configurations were considered for CFD simulation and reported before. The model is of length 10 m, width 2.5 m and height 4.2 m as shown in Fig. 1. The deck height of each level is 2.1 m. There is a staircase of 1.0 m by 1.0 m connecting the upper and the lower deck on the right side of the bus at a distance of 4.0 m from the front plane. The door is on the left side of the bus, of height 1.9 m and width 1.5 m, and 0.5 m from the bus front. Gasoline pool fires with different fuel volume to give different heat release rates Q were set up to study the smoke filling process. Three gasoline fires were used: CF: Circular pool fire of 0.2 m diameter, 100

ml of fuel and steady heat release rate up to 25 kW.

SF1: Square pool fire of side 0.25 m, 500 ml of fuel and steady heat release rate up to 30 kW.

SF2: Square pool fire of side 0.25 m, 700 ml of fuel and steady heat release rate up to 50 kW.

The pool fire was placed at the floor of the lower deck at 5.0 m from the bus front.

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Fig. 1: The 1/10 double-deck bus scale model

On assessing different smoke control schemes, openings were designed. A ceiling vent CV of size 0.5 m by 0.5 m was constructed at the ceiling of the upper deck at a distance of 2.25 m from the bus front. A rear window RW of size 0.5 m by 0.5 m was constructed at the rear part on the upper deck. 3. SCENARIOS IDENTIFIED The following bus scenarios were considered: Test 1: CF, both CV and RW opened. Test 2: SF1, both CV and RW opened. Test 3: SF1, both CV and RW closed. Test 4: SF2, both CV and RW closed.

Test 5: SF2, CV closed but RW opened. Test 6: SF2, both CV and RW opened. Test 7: SF2, CV opened but RW closed.

Measuring points on air temperature inside the model are shown in Fig. 2. There are three thermocouple trees A, B and C, each with ten measuring points labeled as A1, …, A10; B1, …, B10; and C1, …, C10. The thermocouples (A1, B1, C1), (A2, B2, C2), …, (A10, B10, C10) are at the same heights as in Fig. 2b. A1, B1 and C1 are at the highest position, 0.19 m + 0.01 m = 0.2 m below the ceiling. Light sensors are also put as a tree L for smoke measurement reported later.

(a) Location of the sensor trees

5.0 m

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Fig. 2: Air temperature measuring points


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4. RESULTS Results are shown in Fig. 3 to Fig. 9. All those are useful for illustrating how smoke would spread in the double-deck bus. Performance of smoke control scheme can then be evaluated. Further, results are useful for verifying and validating fire models [16].

5. CONCLUSION Double-deck bus fires were studied with a 1/10 scale model. The indoor aerodynamics can be understood. Note that the study is on indoor aerodynamics at the preflashover stage. Results are useful for estimating the evacuation time. Other phenomena such as ignition of second items such as furniture, surface spread of flame over wall, glazing sheet, ceiling and floor are not yet included. Materials should be assessed through full-scale burning tests under flashover as pointed out before.

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ACKNOWLEDGEMENTS The project was funded by a PolyU research grant “Fire Safety in Double-Deck Buses” with account no. G-T838. REFERENCES 1. Apple Daily, Hong Kong, 24 July (1999).

2. Apple Daily, A16, Hong Kong, 6 September (2002).

3. Ming Pao, A13, Hong Kong, 29 November (2002).

4. Inmin Evening, Shanghai, China, 17 August (2005)

5. Apple Daily, Hong Kong, 18 July (2006).

6. W.K. Chow, “Preliminary notes on fire protection in buses”, Journal of Applied Fire Science, Vol. 9, No. 1, pp. 84-103 (2000).

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9. W.K. Chow, “Use of computational fluid dynamics for simulating enclosure fires”, Journal of Fire Science, Vol. 13, No. 4, pp. 300-334 (1995).

10. W.K. Chow, “Observation on the two recent bus fires and preliminary recommendations to provide fire safety”, International Journal on Engineering Performance-Based Fire Codes, Vol. 5, No. 1, pp. 1-5 (2003).

11. W.K. Chow, “Smoke control design for double-deck bus fires with a zone model”, 13th International Heat Transfer Conference, Sydney, Australia, 13-18 August 2006 – Poster presentation (2006).

12. P.J. Fardell, S. Kumar, J.A. Ellwood, J.A. Rowley and S. Vollam, “A study of life threat in bus fires”, Proceedings of Interflam ’93, 6th International Fire Conference, Interscience Communication Ltd., London, U.K., pp. 401-411 (1993).

13. S.J. Mang and O. Keski-Ranhkonen, “Characterization of the fire behavior of a burning passenger car, Part 1: Car fire experiments”, Fire Safety Journal, Vol. 23, No. 1, pp. 17-35 (1994).

14. S.J. Mang and O. Keski-Ranhkonen, “Characterization of the fire behavior of a burning passenger car, Part 2: Parameterization of measured rate of heat release curves”, Fire Safety Journal, Vol. 23, No. 1, pp. 37-49 (1994).

15. M. Shipp and M. Spearpoint, “Measurements of the severity of fires involving private motor vehicles”, Fire and Materials, Vol. 19, No. 2, pp. 143-151 (1995).

16. W.K. Mok and W.K. Chow, “‘Verification and validation’ in modeling fire by computational fluid dynamics”, International Journal on Architectural Science, Vol. 5, No. 3, pp. 58-67 (2004).

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SCALE MODELING RESULTS ON SMOKE SPREADING ......International Journal on Engineering Performance-Based Fire Codes, Volume 8, Number 4, p.145-151, 2006 145 SCALE MODELING RESULTS ON