FIRE AND SMOKE ANALYSIS OF TRAIN FIRE IN AN UNDERPASS Sai Doddi and Ian Ong Hatch Mott MacDonald, Los Angeles, CA
Sequence for this presentation Intro Problem Solution Results
Introduction Underpass is a road tunnel under a highway A growing fire and smoke in an enclosed space can potentially pose a threat to human safety NFPA 130 (National Fire Protection Association) Where supported by engineering analysis, a non-mechanical emergency ventilation system shall be permitted to be provided in lieu of a mechanical emergency ventilation system in the following locations Where the length of the underground or enclosed train-way is less than or equal to 304.8 m (1000 ft) and greater than 61 m (200 ft) The application of tenability criteria at the perimeter of a fire is impractical. The zone of tenability should be defined to apply outside a boundary away from the perimeter of the fire. This distance will be dependent on the fire heat release rate, fire smoke release rate, local geometry, and ventilation, and could be as much as 30 m (100 ft).
Schematic - Underpass and Train
Schematic - Underpass and Train
CFD Model - Underpass and Train
Assumptions/Methodology Medium Fire Growth Curve Heat Source in Car-2 at the center of Underpass Car Fuel is Polystyrene STAR-CCM+ s Fire and Smoke Model - Convective and Diffusive transport of Passive Scalar Doors open at Time=30 seconds Windows break when Temperature=482 F (250 C)
Design Criteria NFPA 130 Smoke obscuration levels should be maintained at levels such that internally illuminated signs are visible at 30 m (100 ft). Client Design Criteria -Flammability and Smoke Emission Maximum heat release rate (HRR) of 13.2 MW (45,000,000 Btu/hr) per car
CFD Simulation Cases Stagnant Wind Case With Wind Case (not presented) Smoke visibility plots produced Egress Analysis STEPS software Pedestrian movement CFD Smoke data imported into STEPS Smoke data in STAR-CCM+ exported as VRML 3d images
STEPS (Simulation of Transient Evacuation and Pedestrian movements) T. Jin and T. Yamada, Irritating Effects of Fire Smoke on Visibility, Fire Science and Technology, Vol. 5 No 1, pp 79-90, 1985 Extinction Coefficient < 0.267 m -1 Normal Walking Speed Extinction Coefficient > 0.267 m -1 Walking Speed will decrease as seen above Visibility m = 8 Extinction Coefficient [m 1 ]
Results Outline 1 Smoke Visibility Plots 2 Egress Analysis Plots 3 Conclusion
Results Smoke Visibility and Egress Analysis Images at 30 second intervals (until 8 min) RED (Untenable): Visibility < 30 m BLUE (Tenable): Visibility > 30 m
Visibility, Time=0 min
Visibility, Time=0.5 min
Visibility, Time=1 min
Visibility, Time=1.5 min
Visibility, Time=2.0 min
Visibility, Time=2.5 min
Visibility, Time=3 min
Visibility, Time=3.5 min
Visibility, Time=4 min
Visibility, Time=4.5 min
Visibility, Time=5 min
Visibility, Time=5.5 and 6 min Windows break at 5.7 min
Visibility, Time=6.5 and 7 min
Visibility, Time=7.5 and 8 min
Animation of Analysis CFD Data integrated with STEPS
CONCLUSIONS CFD Model of Underpass built using STAR-CCM+ and analysis done using Fire and Smoke Wizard Visibility plots generated in the analysis Egress analysis performed shows that passengers evacuate to safety without the need for any additional mechanical ventilation
Acknowledgements Kenneth Li for performing the STEPS analysis for the study
QUESTIONS?
APPENDIX
Geometry details Proposed length of covered Section 270 ft increased to 316 ft Height of Underpass reduced from 18.5 ft to 16.75 ft Width of Underpass is 32 ft Gradient is -0.02% (North portal lower than South portal) Train floor is 1.5 ft above Underpass floor Top of Rail is 9 above Underpass floor