Syudy Of Fire Characteristics In Loog Subway Tunnels With Point Extraction Ventilation Systems

Relatively, tunnel space is narrower than architecture that caused great difficulties for evacuation and fire fighting, which because of the high temperature and the numerous smoke in tunnel fires. So we must take measure to control the tunnel fire smoke, and the longitudinal ventilation is the most commonly used method. It has certain limitations in deep buried long tunnel fires when the longitudinal ventilation is used. Because this way may make the downstream yet in the burning train in the dangerous when there are two trains in the long subway tunnel. Therefore, the point smoke extraction method was put forward in this article.In the paper we applied the 3-d numerical simulation technique (FDS) to study single-point extraction ventilation system and two-point extraction ventilation system based on two-tube long subway tunnels which with an independent exhaust duct. The point extraction ventilation system was operated under different fire loads and fire vertical position and exhaust vent size and fire-vent distance and exhaust volume. The main results are as follows:The results of smoke diffusion characteristics in tunnel fire with single-point extraction ventilation system showed that the smoke parameters of downstream tunnel changed sharply under the vent as the smoke exhaust thought it, while parameters of upstream tunnel which without vent changed smaller. Studies also have shown that all the factors can improve the smoke parameters of downstream tunnel and exhaust vent size and exhaust volume were the main influence factors. Increasing the width of the vent can effectively prevent the smoke flow around. While the exhaust volume was big enough to generate large cross-section average wind speeds which toward to the fire in both upstream and downstream (this paper was 160m3/s), the smoke parameters were conform to the smoke control standard in tunnel fires and the smoke exhaust efficiencies were greatly increased, however, that volume was too heavy to the extraction ventilation systen. That means the single-point extraction ventilation system is not desirable in the practical engineering.The results of smoke diffusion characteristics in tunnel fire with two-point extraction extraction ventilation system showed that the smoke parameters of both up and down-stream tunnels changed sharply under the vents as the smoke exhaust thought them. The influence of factors such as fire loads and exhaust vent size were the same between single and two-point extraction ventilation systems, while the later was superior to the former. The paper also showed that the worst fire location was fire just off one of the vents, no matter the distance was 30m or 60m. In the end, the paper analysd the influence of exhaust volume based on the worst fire location, which showed that the exhaust efficiencies increased and the speeds of exhaust efficiency decreased while increasing the exhaust volume. However, the exhaust efficiencies tended to be 100% and the speeds of exhaust efficiency tended to be 0, when the exhaust volume was increased to a certain value (this paper was 60m3/s). In addition, the exhaust volume of two-point extraction ventilation system would just be 37.5% times of that of single-point extraction ventilation system when the exhaust efficiencies of two system were the same.