Guidelines for Emergency Ventilation Smoke Control in Roadway Tunnels (2017)

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1 S U M M A R Y This report provides guidance to the owners and agencies, law enforcement agencies, first responders, designers, and vendors in reference to emergency tunnel ventilation. It can also be used by state departments of transportation (DOTs) for implementing best practices within their tunnel operation program in order to improve public and emergency responder safety. The tunnel ventilation system is the main tunnel fire life safety system. An objective of the tunnel ventilation system is to control and/or extract smoke and heated gases and to provide a non-contaminated environment for egress of tunnel users. Another objective is to support firefighting and rescue operations. In both cases, the primary goal is to control smoke and hot gases as the result of fire. Choosing the type of ventilation system is one of the most important decisions when designing a tunnel. While every situation has its unique features, some general conclusions are drawn about the relative usefulness and efficiency of the various types of ventilation systems for smoke control. Memorial Tunnel fire tests sponsored by FHWA, American Society of Heating, Refrigerat- ing and Air-Conditioning Engineers (ASHRAE), and others concluded that full transverse and semi-transverse ventilation systems used in many old U.S. tunnels designed to the old standards and installed over 40 years ago, were ineffective in the management of heat and smoke for fires of 20 MW (bus fire) or larger. To manage large fires, the old systems may need to be modified. Nowadays, there are two commonly used concepts for smoke management in road tunnels to achieve a smoke free environment for egress: • Longitudinal ventilation concept—directing smoke along the tunnel in the opposite direc- tion of egress by completely pushing the smoke to one side of the fire (preferably applied to non-congested uni-directional tunnels where there are normally no people down- stream of the fire and is typically achieved by longitudinal ventilation). It introduces air into or removes smoke and gases from the tunnel at a limited number of points, primar- ily by creating longitudinal airflow through the length of the tunnel, from one portal to the other. Longitudinal ventilation can be accomplished either by injection, central fans, jet fans mounted within the tunnel, nozzles (often installed at the portals and called a Saccardo system), or through a combination of injection and extraction at intermediate points. The system must generate sufficient longitudinal air velocity called “critical velocity” to prevent backlayering of smoke. • Extraction ventilation concept—extracting smoke at the fire location by keeping the smoke stratification intact, leaving more or less clean and breathable air suitable for evacuation underneath the smoke layer to both sides of the fire (applicable to bi-directional or congested uni-directional tunnels and is typically achieved by zoned transverse ventilation or single point extraction). Extraction ventilation concept typically requires exhaust ventilation Guidelines for Emergency Ventilation Smoke Control in Roadway Tunnels

2ducts and a system capable of localizing hot gases and smoke and extracting them at the fire location using exhaust high temperature rated ventilation fans. The document provides a roadmap for selecting a tunnel ventilation system and types of tunnel ventilation fans. Fixed firefighting systems, where provided, shall be coordinated with ventilation. Tunnel ventilation system response shall be coordinated with fixed firefighting system response and properly documented in the emergency response plan. Fixed firefighting systems cannot replace the tunnel ventilation system; however they could reduce the fire size, fire growth and ventilation requirements. Every tunnel should have a comprehensive emergency response plan and concept of tunnel operation documents. These documents should address specific instructions to the tunnel operators on how to operate the tunnel ventilation system during fires inside and in the vicinity of the tunnel and other possible scenarios considering the unique nature of the tunnel. The strategies may differ depending on the type of ventilation system, traffic con- ditions, presence of other fire life safety systems such as fixed firefighting systems, and phase of fire emergency (evacuation or firefighting phase). The control system should allow for the response of the ventilation system to a reported incident in accordance with the emer- gency response plan. This response is based on information retrieved from various sources inside and outside the tunnel. The information is analyzed and validated and the ventilation response could be activated automatically, semi-automatically, or manually. Consideration needs to be given to the complexity of the ventilation system, other tunnel fire life safety systems and the organization of the operating personnel. A complex ventilation system is much more efficiently managed by an automatic or semi-automatic system than by an opera- tor performing under high stress conditions. The ventilation control should ensure adequate response for all conceivable fire scenarios including scenarios where some equipment or sensors fail to respond. Control methods must take into account that the conditions may change over time. Different tunnels may require different control approaches. The general recommendations to the operators applicable to all fire situations are: • Respond in a timely manner to save lives; • Activate fire life safety systems, such as tunnel ventilation, in accordance with the emer- gency response plan; • Do not blow smoke in the direction of evacuees. Direct fresh air to support evacuation; • Do not change the selected ventilation mode without direction from incident commander, especially during the evacuation phase. Changing ventilation mode, such as reversing fans or airflow during a fire event, could spread smoke throughout the tunnel; • Over-ventilating may increase the fire size and fire growth rate and may destroy smoke stratification; • Periodic training of tunnel operators, first responders, and their interactions is essential for a successful response. Training simulators are useful tools for ventilation controls training. The document evaluates the fire safety risks for different type of tunnels depending on tunnel length and usage and provides general mitigation means and strategies for each general case. As far as fire and rescue services are concerned, the most important measures that can reduce the severity of accidents are: • Short distances to, and simple means of reaching escape routes for those escaping from a fire and rescue work;

3 • Firefighters can approach the fire as safely as possible (in protected environment) and safely escape as needed; • Fire cannot grow excessively before firefighting work can start. These various conditions can be achieved in different ways, but there must be an overall safety program that identifies all the parameters involved, ensures that they work together, and creates the best conditions for a high level of safety.