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

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67 Tunnel Fixed Firefighting Systems Fixed firefighting systems (FFFS) are being installed in many new road tunnels and as retrofits to existing tunnels both within the United States and internationally. Today, nearly 200 tunnels around the world are equipped with active fixed water-based firefighting systems. Fixed water-based firefight- ing systems have been successfully used for more than 50 years in Japan’s congested urban road tunnels and, lately, in all of Australia’s congested urban tunnels. In the U.S., the system has been first installed in a few tunnels over 40 years ago. NFPA 502 established the goals of a fixed water-based fire- fighting system to slow, stop, or reverse the rate of fire growth or otherwise mitigate the impact of fire to improve tenabil- ity for tunnel occupants during a fire condition, enhance the ability of first responders to aid in evacuation and engage in manual firefighting activities, and/or protect the major struc- tural elements in the tunnel [1]. It should be noted that all water-based firefighting systems are limited in their ability to fight fires inside or underneath vehicles. However, their abil- ity to extinguish small open tunnel fires is recognized. It is to be expected that a fire in obstructed locations will continue to burn after activation of the FFFS. Thus, the main purpose of the FFFS is to mitigate the impact of a fire. Even after activa- tion, tunnel users and emergency personnel should anticipate fire in the tunnel when escaping from or approaching the area of risk. There are many types of water-based firefighting systems but only a few that are found to be applicable to the tunnel environment. Restrictions, such as open portals, natural venti- lation and huge tunnel volumes, prevent the practical applica- tion of most suppression systems. The two types of water-based fire suppression systems found to present the most benefits in the tunnel environment are deluge sprinklers and intelligent water mist. • A deluge zone system with open sprinkler heads is the most commonly used system. A deluge water spray system sup- presses a fire mainly by fuel surface cooling. This system can be with or without foam additives depending on the type of vehicles allowed in the tunnel and type of tunnel risk level. They are used as fire suppression systems and fire control systems once designed with sufficient water flow for the fire scenario. They can be applied for surface cooling as well. • A water mist system typically has less water density, higher pressure, and smaller water droplet sizes than the deluge system. A water mist system suppresses a fire mainly by dilution and gas cooling. This system could be very effec- tive as a volume cooling system to cool the tunnel environ- ment using high pressure water mist or as a surface cooling system. • Other systems such as sprinkler systems with fusible link or high expansion foam systems are less common. Glass bulb type activated fixed water-based systems in which sprin- klers, spray heads, or other components are activated or controlled individually by thermal elements, such as glass bulbs, are not recommended for road tunnels considering the fire risk present in tunnels and the rapid development of fires and hot smoke. Fire tests have proven that indi- vidually activated sprinklers/spray heads do not provide the required level of protection and are very sensitive to the effects of ventilation. The efficiency of a water-based firefighting system is strongly dependent on the size of the fire (or heat generation rate), nozzle type, location, and the water discharge rates. Applicability of Tunnel Fire Suppression Systems NFPA 502 does not require mandatory application of a tunnel fire suppression system to all tunnels. The applicabil- ity of a tunnel fire suppression system depends on the level of risk the tunnel is exposed to and should be applied to long, high risk tunnels. A p p e n d i x B

68 Fire suppression systems differ by water density, water pres- sure, foam additives, and their applicability. In addition to the objectives discussed in Chapter 5, the applicability of a FFSS depends on the following: • potential fire risk, • level of protection, • other safety measures in the tunnel, • tunnel geometry, • ventilation/wind conditions during a fire, including inter- action with emergency ventilation, • type and performance of the fire detection systems, • activation mode of the suppression system, • any restrictions in positioning and fixing the pipework or nozzles, • distance to emergency exits, • signage and lighting, • thermal conditions in the tunnel and its surrounding, and • any specific requirements for the operation of the tunnel. Fire detection and activation of the fire suppression system are essential elements in the design of the fire suppression system and in the ability of the system to meet its objectives, especially for the large fires. For effective deluge operation, activation should be rapid and accurate. If discharged rap- idly enough, the fire growth rates will likely be controlled, the risk of rapid fire spread minimized, and toxic gas and smoke generation volumes contained. If all ignition sources cannot be extinguished and the site is uniformly cooled below a safe temperature, the fire could reignite. Figure B.1 schematically shows the effect of a FFSS on HRR [46]. With timely activation of the suppression system, the heat release rate is reduced. With delayed activation of the system, the fire overwhelms the system and it may not be effective. It is vital to have a clear understanding of the capabilities of the detection system and the lead-in times for activation of the fire life safety systems. If timely detection is not achieved and the fire is not detected until it enters its rapid growth phase, the resultant fire will, in all likelihood, be well beyond the capabilities of a FFSS once it is activated [45]. While a few automatic sprinkler systems have been installed in tunnels, most systems are deluge systems. The entire pro- tected area is covered with nozzles which are grouped into zones. A deluge system has a network of open nozzles at the roof of the tunnel, divided into zones occupying the entire width of the tunnel. These zones are typically 20–35 m (65–120 ft) long, a distance which is based off the length of a heavy goods vehicle and the tunnel geometry. When there is a fire, a deluge valve is opened in the zone above the fire and in the zone on either side of it. Water is sprayed from all the nozzles in the activated zones. The sizing of the zone lengths should be based on an analysis taking into account the design fire. In case of activation of the FFFS (automatically by detec- tion system or manually), at least one deluge valve will be opened accordingly and at least one pump unit will be started. The pump system capacity should be adequate to provide water and, where applicable, additives simultaneously for at least the defined minimum number of zones (normally two or three) at the minimum nozzle pressure at any location in the protected area. Pump system redundancy should be con- sidered. The system should be robust and have a minimum of one redundant pump. The tunnel fire suppression equipment and piping should be designed based on a hydraulic analysis and should consider a longevity of at least 20 years and operation in a harsh tun- nel environment with salted and humid air, vehicle exhaust Figure B.1. Schematic effect of suppression on heat release rate [46].

69 pollution, particles from brakes, dirt and dust, and should be protected from corrosion. In systems using additives, the temperature of the firefighting agent should be taken into account for the determination of viscosity, depending on the minimum temperature in the tunnel. All materials used should be in accordance with the requirements of the FFSS manufacturer. The FFSS should be protected from dam- age by vehicles. The FFSS should be designed for operation throughout the range of expected temperatures. Temperature ratings of all components should be suitable for the operat- ing temperatures during standby and operation. The effects of thermal expansion on pipework which is dry before activa- tion should be calculated by applying an engineering method using a design temperature of at least 250°C (482°F) or at temperatures deemed appropriate. The impact of water hammer should be taken into account in the design of the FFSS. Water hammer typically occurs in the FFSS when deluge or section valves are closed too fast or empty pipes are filled (system deactivation or changing acti- vated sections). Water hammer creates a pressure surge that can be critical especially for low-pressure systems and their components. Thus, all valves should be designed in such a way that this phenomenon is avoided. Water hammer occurs only if valves are closed faster than the critical valve closing time, which is the time it takes for the pressure wave to travel through the pipework. When defining critical closing time tc, a safety factor of two should be applied. The calculation for the critical closing time is as follows: 200% 2 26t L B c pipe W [ ]= ρ where Lpipe = pipe length between the pump and the valve Bw = Bulk modulus of agent (for water at 20°C: 2.1⋅109N /m2) [N/m2] r = density (water 20°C: 998 kg/m3)[kg/m3] Flushing of the pipework should be planned and carried out according to the manufacturer’s requirements. Pipes should be protected with plugs during installation to prevent access of foreign material. Pressure testing should be carried out in accordance with relevant standards at 1.5 times the design pressure and witnessed by the AHJ [26]. Deluge systems have been selected over automatic sprin- kler systems for three reasons. First, heat from a fire does not stay over the fire, but travels along the tunnel with airflow. This requires a fire detection and suppression system that can adequately deal with a fire that has heat and smoke dispersed far away from its source. Second, the tunnel fire could rap- idly develop a great deal of heat over a large area so that too many sprinklers would open, overwhelming the water sup- ply. Third, automatic sprinklers lack flexibility. By contrast, a deluge system takes a fixed amount of water, and with suit- able detection, it is possible to open only the zones above or next to the fire. Deluge water spray nozzles take water at a typical pressure of 1.5 to 5 bar (21.8 to 72.5 psi) and discharge a pattern of water droplets over the area below. Water spray systems are designed to achieve an even discharge of water over an area, with one specification being the water application density, measured like rainfall in mm/min. Droplets from water spray systems are typically larger than 1 mm (0.04 in.) in diameter. Water application rate (water density) should be designed based on the objectives of the system (Figure B.2). If the objective is fire suppression, the water density should be evaluated based on the FHRR at the time the deluge system is fully activated. The deluge systems may require substantial amounts of water, which can have a significant impact on the storage, delivery, and drainage systems. Water mist systems require less water per zone than deluge systems. Japan and Australia each have their own specified water application rates to be used for road tunnel FFFS design, which are 6 mm/min (0.15 gpm/ft2) and 10 mm/min (0.25 gpm/ft2) respectively. In full-scale tunnel sprinkler tests conducted in Europe Figure B.2. NFPA 13, NFPA 15, and other international water application rates [47].

70 (2nd Benelux), a water application rate of 14 mm/min (0.35 gpm/ft2) has been tested. In 2011–2012, fire tests were performed at the San Pedro Des Anes test tunnel facility in Spain sponsored by the Land Trans- port Authority of Singapore. A water flow rate of 8–12 mm/ min with a nozzle operating pressure of 1–2 bar (14.5–29 psi) demonstrated the reduction of a FHRR from 115/150 MW (392/512 MBtu/hr) to less than 40 MW (140 MBtu/hr) when the system was activated at 4 minutes after the fire was detected (see Figure B.3). This corresponded to a 60°C (140°F) gas temperature measurement below the ceiling [48]. The fire test program was carried out for the purpose of investigating the influence of a deluge fixed firefighting system on peak fire heat release rate and to acquire information on the appropriate design parameters (e.g., nozzle type, discharge density, and acti- vation time). The test program included one free-burn test and six tests with different deluge system arrangements (Table B.1). All fire tests were carried out with a longitudinal ventilation velocity of approximately 2.8–3 m/s (550–600 fpm). In U.S. tunnels equipped with a FFSS, the water applica- tion rate varies from 0.16 to 0.35 gpm/ft2 (6.6 to 14 mm/min, see Figure B.4) depending on the type of vehicles allowed, the Figure B.3. HRR for HGV Fire with and without fire suppression [48] and with delay 8 min activation of FFSS (test 6). Table B.1. Large scale fire tests schedule [48].

71 hazards in the tunnel, risk level, and tunnel geometry. Note that 1 kg (2.2 lb.) of water can absorb about 2.6 MJ (2500 Btu) of heat by evaporation to become water vapor at a temperature of 100°C (212°F). The amount of water required for fire sup- pression needs to be equal to the heat absorbed by the fuel sur- face at the time of discharge, rather than the total HRR. Note that to effectively suppress a well-developed fire, the water flow rate needs to be greater to assure that enough water droplets are able to penetrate the fire plume and reach the fuel surface before evaporation, or that enough water vapor is produced to cool the flame and dilute the combustion mixture. Figure B.4 shows the sample curves of fire heat release rates for varying water application rates for unshielded fires. (This example is for illustrative purposes developed only for a specific tunnel geometry and traffic conditions.) A water-based FFSS with foam additives such as 3% AFFF (Aqueous Film Forming Foam) should be considered for tun- nels that allow flammable and combustible vehicles. This sys- tem uses 97% water and only 3% foam which once discharged creates a thin film of foam on the roadbed surface which iso- lates light combustible or flammable liquids from oxygen and cools down the fuel pool to suppress the fire. The water den- sity should be calculated the same way as if there is no foam. Tests demonstrated that the system can completely extinguish a small diesel pool fire within 30 seconds after activation and can control a fire if the fuel pool is shielded from direct sprin- kler droplets exposure [49]. It was noted that the temperature inside the van was reduced as water droplets were blown into the van through the open windows when the FFSS was active with 3% AFFF additives and a 2 m/s (400 fpm) air velocity was applied to a shielded diesel fire inside the van. If the objective is volume or surface cooling, the results of the comparative analyses suggest that water application rates as low as 2 mm/min (0.05 gpm/ft2) can offer some benefits by cooling exposed surfaces and assisting in limit- ing the spread of fire from the initiating point. A water mist system can be effective to achieve the volume or surface cooling objectives. The water mist system, which gained popularity due to water conservation and saving space within the tunnel, has been installed in several European tunnels and could be effective for volume or surface cooling. A water mist system is similar in zoning and operation to the deluge system with the exception that it utilizes different kinds of water drop- lets (density, droplet sizes, pressure and so forth). Water mist systems use much lower water density, on the order of 1–4 mm/min (0.024 to 0.098 gpm/ft2). A comparison of a water mist system with a deluge system is shown in Table B.2. Water mist systems use higher pressures, in some cases over 100 bar (1450.4 psi), and discharge small water droplets, 99% of which have a diameter less than 1mm (0.04 in). Water mist systems can be subdivided into low-pressure water mist (about 10 atm [147 psi]) and high pressure water mist sys- tems (in the range of 80 atm [1180 psi]). Nozzles with very small orifices are used to create the mist. The smaller droplets are drawn into the fire and easily evaporate due to the large surface area to volume ratio. The mist systems may require less water per zone. Storage tanks, pumps and pipes can be smaller as well, saving on costs. To operate effectively, the FFSS has to be properly main- tained, periodically tested and it must survive the event. Figure B.4. Fire heat release rate for varying water application rates—unshielded fires [47].

Table B.2. Comparison of water mist and deluge systems components.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

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