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A modified critical velocity for road tunnel fire smoke management with dedicated smoke extraction configuration

机译：具有专用排烟配置的公路隧道火灾烟气管理的改良临界速度

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摘要

Life safety is one of the objectives of fire engineering design for road tunnels. Fire engineering design requires maintaining a tenable condition for a period of time to allow occupants to evacuate to safety. This will be achieved by controlling the smoke under credible design fire scenarios in a tunnel. The critical location in a tunnel fire emergency condition is the tunnel region upstream of the fire, where occupants are most likely to reside as traffic jam can usually be created by the fire incident. Tenability for the downstream region of fire is not the main focus of this research because vehicles can generally drive out of the tunnel at a higher speed than that of the smoke flow, and local damper smoke extraction can help keep a tenable condition in the downstream region beyond the local fire zone, in case there is a congestion in the downstream region of the fire. To maintain a tenable condition in the upstream tunnel region from the fire incident, the required minimum longitudinal flow velocity to prevent smoke backlayering can be calculated based on NFPA 502 recommendations. This critical velocity takes no credit of the smoke extraction or active overhead fixed fire suppression effects. Smoke extraction with a dedicated smoke duct along the entire length of the tunnel is gaining popularity because of its efficiency and robustness in providing a tenable environment in the tunnel with unknown upstream and downstream traffic conditions. In this paper, a modified critical velocity to control smoke back-layering while smoke extraction and fire suppression systems are operating has been analyzed. This modified critical velocity is approximately 20% lower than the critical velocity that is recommended in NFPA 502. This allows significant savings on ventilation capacity for road tunnels which have a local smoke exhaust capability using a dedicated smoke duct. It is concluded that the smoke extraction performance is similar whether using ceiling dampers or vertical wall-mounted dampers for smoke capture to maintain tunnel tenability. However, tunnel gradients play a major role on the modified critical velocity for a nominated design fire and the required smoke extraction rate.
机译：生命安全是公路隧道消防工程设计的目标之一。消防工程设计要求保持稳定的状态一段时间，以使居住者能够撤离到安全地点。这将通过在可靠的隧道设计火灾情况下控制烟雾来实现。隧道火灾紧急情况下的关键位置是火灾上游的隧道区域，由于火灾通常会造成交通拥堵，因此居民最有可能居住。下游火灾的持久性不是本研究的主要重点，因为车辆通常可以以比烟流更高的速度驶出隧道，而局部阻尼器烟雾的抽出可以帮助保持下游地区的持久性如果火灾下游区域发生拥堵，则超出本地火灾区域。为了在发生火灾后在上游隧道区域保持稳定的状态，可以根据NFPA 502的建议计算所需的最小纵向流速，以防止烟雾回覆。这个临界速度不考虑烟雾的排出或主动架空固定灭火的效果。由于沿隧道的整个长度提供专用烟道的排烟技术越来越受欢迎，因为它在隧道的上游和下游交通状况未知的情况下提供了一个可承受的环境，因此具有很高的效率和鲁棒性。本文分析了一种改进的临界速度，用于在排烟和灭火系统运行时控制烟层的回覆。修改后的临界速度比NFPA 502中建议的临界速度低大约20％。这可以大大节省具有专用烟道的局部烟气排放能力的公路隧道的通风量。得出的结论是，无论使用天花板风门还是垂直壁装风门进行烟雾捕获以保持隧道的延展性，烟雾的抽出性能都相似。但是，对于指定的设计火灾和所需的排烟率，隧道坡度在修正的临界速度上起着重要作用。

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