A study on long tunnel smoke extraction strategies by numerical simulation

The performance of different smoke extraction strategies for a long vehicle tunnel was investigated for a 100 MW fire scenario. Computer modeling was used for the investigation with a numerical simulation method. The selection of single-point extraction (SPE) opening strategy versus multi-point extraction (MPE) opening strategy was analyzed. In the single-point extraction (SPE) opening strategy, the smoke spread was found to be contained between the fire site and the point of smoke extraction. This result was obtained when the tunnel air velocity reached the critical velocity for preventing back-layering of smoke. For multi-point extraction (MPE) strategies with more than one opening, the smoke spread to all the extraction openings. Moreover for MPE strategy, air velocities were found to be slower near the middle openings and could be less than the critical velocity. Distributions of smoke spread, CO, visibility and temperature were analyzed. It was found that visibility of smoke and temperature were the key factors for safe evacuation of the personnel in tunnel. The SPE system was found to be more effective than the MPE system for partial transverse ventilation systems.