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Design Fires in Road Tunnels (2011)

Chapter: Chapter Six - Fire Tests Literature Review

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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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Suggested Citation:"Chapter Six - Fire Tests Literature Review." National Academies of Sciences, Engineering, and Medicine. 2011. Design Fires in Road Tunnels. Washington, DC: The National Academies Press. doi: 10.17226/14562.
×
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29 Fire tests are of vital importance in the understanding of the physics of tunnel fires, understanding the impacts of fires, and for verifying calculations, assumptions, computer models, and tunnel design. They are also important for tunnel opera- tors and emergency responders in their efforts to coordinate and verify in practice the emergency response plans. The fire tests that have been performed can be classified as: • Tests before the design to develop design methodology. • Tests during the design to verify assumptions and com- puter models. • Tests during commissioning to verify the design and equipment operation. • Tests for training purposes. • Other tests as needed. Important work has been conducted at full-scale (large- scale) tunnels, including: • EUREKA tests • Memorial Tunnel Fire Ventilation Test Program • Runehamar Tunnel fire tests • Full-scale tests in Norway • Tests in Japan. Experimental tests and especially their replications are expensive and there is a lack of willingness to carry them out. However, it is very important to perform tunnel fire tests and there is a need for multi-agency and international collaboration. FULL-SCALE TESTS Full-scale tests are often expensive to carry out. They require access to a tunnel or to a full-scale mock-up with some basic installations. Large-scale and full-scale fire tests with HRRs of 100 MW (341 MBtu/hr) or more require normal modifications and protection of the lining and installations. Measuring the fire size (in terms of the HRR) needs advanced instrumentation and data analysis. Some lessons learned during the previous large-scale tests included: • Lack of control of the conditions of the experiments (e.g., humidity). • Lack of careful design of the experiment (location of thermocouples and other instrumentation). • Measurement errors (e.g., low-velocity measurement by inappropriate instrumentation). • Raw data processing algorithms and subjective judgments (e.g., visibility judgments based on video recording). Each full-scale program had its own objectives and goals, which drove methodology and resultant conclusions, mak- ing it difficult to generalize findings from the historical test data results. There is a great need for more large-scale testing to be able to better understand the fire and smoke dynamics. However, the tests must be carefully designed and equipped with appro- priate instrumentation. Research programs using full-scale facilities generally deal with numerous but very specific aspects of safety character- ized by high human and economic stakes. They require signif- icant financial support. The main large-scale test programs that have been performed follow. Ofenegg Tunnel Tests To gain at least a general impression of the temperature conditions and the amount of smoke to be expected from a gasoline fire, evaluations of the performance of the fixed fire suppression system tests were performed in the Swiss Ofenegg Tunnel and in the Zwenberg Tunnel in Austria. Both test facilities were abandoned railroad tunnels. Two types of ventilation systems, longitudinal and semi- transverse supply, were evaluated. The tunnels had no exhaust provisions. Sprinklers were mounted over the fuel basin and their effectiveness was evaluated. Eight tests were scheduled with different ventilation systems: • Natural • Longitudinal • Semi-transversely • With sprinklers for 500 L (132 gal.) fuel fire • With sprinklers for 1,000 L (264 gal.) fuel fire. Test results raised doubt of the effectiveness of sprinklers in containing a fire or in limiting the range and severity of damage. A delay in activation may produce a significant vol- ume of high temperature steam as dangerous as the combus- tion products. If all ignition sources cannot be extinguished CHAPTER SIX FIRE TESTS—LITERATURE REVIEW

and the site uniformly cooled below a safe temperature the fire may reignite, perhaps explosively, when the sprinklers are shut off. Meanwhile, unburned vapors spread throughout the tunnel and ventilation ducts are at great hazard far from the fire, even if the fire is extinguished. (Additional test descriptions can be found in web-only Appendix E.) Zwenberg Tunnel Tests This program was initiated in 1975 in connection with two major motorways projects in Austria (21). Longitudinal and semi-transverse ventilation systems were tested. The tests included a total of 30 pool fires. (See web-only Appendix E for additional information on the tests.) Because the test results so strongly supported the benefits of a fully transverse system running in a full extraction mode during a fire, the investigators made the following recom- mendations for the design and operation of a tunnel ventila- tion system: • The very rapid development of a fire requires a suitable pattern of ventilation for creating the best possible con- ditions for rescue. • To fulfill this requirement it is necessary – that the fire is quickly detected and the alarm trans- mitted to a tunnel control center where the operating pattern can be selected, and – that the appropriate technical and organizational measures be prepared, securing a fast and correct selection of the operating pattern of the ventilation system in the case of a fire. • The tunnel must be equipped with a quickly responding fire warning system. Signals are to be transmitted with minimal possible delay to the control center. • The primary goal must be to prevent the spread of hot fumes and smoke in the traffic space. • This recommendation must be implemented without any restriction in all tunnels with two-way traffic. Public Works Research Institute Experiments PWRI experiments (21) (Japan 1980) are described in web- only Appendix E. The PWRI test report concluded that: • Smoke can be kept within the minimum space and be extracted quickly if the kinetic energy of the smoke flow produced by the thermal energy of fire is less than the energy of ventilating air blowing along the tunnel toward the smoke ventilation dampers when the fans are run in reverse direction. This is achieved by the rela- tionship between the scale of the fire and the capacity of the fans (i.e., if the fire is too big, the fans will not extract all of the smoke). • Ventilation fans are generally designed for the pur- pose of reducing the concentration of exhaust gases 30 from vehicles and extending the visible distance by tak- ing into consideration estimated traffic volume, tunnel length, natural ventilation, ventilation by movement of vehicles, and so forth. Depending on these design con- ditions, there may be a small number of cases in which smoke can be reasonably extracted by existing ventila- tion systems. • Stratification of smoke was partially destroyed by longi- tudinal ventilation at 1 m/s (197 fpm) and totally des- troyed by longitudinal ventilation at 2 m/s (394 fpm). • For determining the capacity of ventilating fans in the future, the fire smoke exhaust capacity of the fans shall be designed to meet the scale of a real vehicle fire. • The sprinklers had an adverse effect on the tunnel envi- ronment by causing a reduction in smoke density near the ceiling and an increase in smoke density in the lower part of the tunnel. • None of the car, bus, or pool fires was totally extin- guished by the sprinklers; however, the heat generation speed was reduced in each case. Repparfjord Tunnel Tests Tests were undertaken at the Repparfjord Tunnel near Ham- merfest, Norway from 1990 to 1992 (21). That test report concluded that: • The influence of damage both to the vehicles and tunnel lining, especially in the crow area, depends on the type of vehicle. The roofs of those vehicles constructed of steel resisted the heat, whereas the roofs of the vehicles made of aluminum were completely destroyed during an early stage of the fire. • The temperatures during most of the vehicle fires reached maximum values of 800°C to 900°C (1472°F to 1652°F). The temperatures during the HGV test reached 1300°C (2372°F). Temperatures decreased substantially within a short distance from each fire location and were greater downwind than upwind. • The HGV burned at an HRR of more than 100 MW (341 MBtu/hr). • Fast fire development registered in the first 10 to 15 min. Growth rates of vehicle fires vary from medium to ultrafast. • Longitudinal ventilation destroyed stratification down- wind of the HGV fire. Benelux Tunnel Tests In the Benelux Tunnel, 14 fire tests were used to determine the benefits of fitting large drop sprinklers. These sprinklers were selected so that the large droplets would penetrate the power- ful fire plumes and not be swept away by the tunnel ventilation. In the tests, with ventilation at up to 5 m/s (984 fpm), sprin- klers reduced temperatures to safe levels upstream and down- stream of the fire. They also reduced the probability of fire

31 spread between vehicles. Results of these tests are discussed in the chapter thirteen. Memorial Tunnel Tests The Memorial Tunnel tests (United States, 1993–1995) (21, 25, 26) were financed by the FHWA and the Commonwealth of Massachusetts for the Boston Central Artery Tunnel proj- ect. The experiments were performed in an abandoned 854-m (2,800-ft)-long road tunnel located in West Virginia. Approx- imately 90 tests were done with diesel oil pool fires. The obtained HRRs varied from 10 MW (34 MBtu/hr) for a 4.5 m2 (48.4 ft2) area to 100 MW (341 MBtu/hr) for a 44.4 m2 (478 ft2) area. There were 1,450 devices installed in the tun- nel, providing about 4 millions points of data per experiment. (See web-only Appendix E for test facility description.) The Memorial Tunnel program performed tests with fire sizes of 10, 20, 50, and 100 MW (34, 68, 172, and 341 MBtu/hr). The tests were done with various ventilation systems including: • Full-transverse Ventilation—Air is uniformly supplied and exhausted throughout the entire length of a tunnel or tunnel section. • Partial Transverse Ventilation—Either supply air or exhaust air, but not both, is uniformly delivered or extracted throughout the entire length of a tunnel. • Partial Transverse with Single-Point Extraction—A series of large, normally closed exhaust ports distrib- uted over the length of the tunnel to extract smoke at a point closest to the fire. • Partial Transverse with Oversized Exhaust Ports— Normally closed exhaust ports that automatically open in a fire emergency. • Natural ventilation. • Longitudinal ventilation with jet fans. Longitudinal Tunnel Ventilation Systems A longitudinal ventilation system employing jet fans is highly effective in managing the direction of the spread of smoke for fire sizes of up to 100 MW in a 3.2% grade tunnel. The throt- tling effect of the fire needs to be taken into account in the design of a jet fan longitudinal ventilation system. Jet fans that were located 51.8 m (170 ft) downstream of the fire were subjected to the following temperatures for the tested fire sizes: • 204°C (400°F)—20 MW fire • 332°C (630°F)—50 MW fire • 677°C (1250°F)—100 MW fire. Air velocities of 2.54 m/s to 2.95 m/s (500 fpm to 580 fpm) were sufficient to preclude the backlayering of smoke in the Memorial Tunnel for fire tests ranging in size from 10 MW to 100 MW. Single-Zone Transverse Ventilation Systems Single-zone, balanced, full-transverse ventilation systems that were operated at 0.155 m3/s/lane-meter (100 ft3/min/ lane-foot) were ineffective in the management of smoke and heated gases for fires of 20 MW (68 MBtu/hr) and larger. Single-zone, unbalanced, full-transverse ventilation systems generated some longitudinal airflow in the roadway. The result of this longitudinal airflow was to offset some of the effects of buoyancy for a 20 MW fire (68 MBtu/hr). The effectiveness of unbalanced, full-transverse ventilation systems is sensitive to the fire location, because there is no control over the airflow direction. Multiple-Zone Transverse Ventilation Systems The two-zone (multi-zone) transverse ventilation system that was tested in the Memorial Tunnel Fire Ventilation Test Program provided control over the direction and magnitude of the longitudinal airflow. Airflow rates of 0.155 m3/s/lane- meter (100 ft3/min/lane-foot) contained high temperatures from a 20 MW (68 MBtu/hr) fire within 30 m (100 ft) of the fire in the lower elevations of the roadway and smoke within 60 m (200 ft). The spread of hot gases and smoke was significantly greater with a longer fan response time. Hot smoke layers were observed to spread very quickly, from 490 m to 580 m (1,600 ft to 1,900 ft) during the initial 2 min of a fire. Natural ventilation resulted in the extensive spread of smoke and heated gases upgrade of the fire, but relatively clear condi- tions existed downgrade of the fire. The spread of smoke and heated gases during a 50 MW (171 MBtu/hr) fire was con- siderably greater than for a 20 MW (68 MBtu/hr) fire. The depth of the smoke layer increased with fire size. A significant difference was observed between smoke spread with the ceiling removed (arched tunnel roof) and with the ceiling in place. The smoke and hot gas layer migrat- ing along the arched tunnel roof did not descend into the roadways as quickly as in the tests that were conducted with the ceiling in place. Therefore, the time for the smoke layer to descend to a point where it poses an immediate life safety threat is dependent on the fire size and tunnel geometry, specifically tunnel height. In the Memorial Tunnel, smoke traveled between 290 m and 365 m (950 ft and 1,200 ft) along the arched tunnel roof before cooling and descending toward the roadway. The restriction to visibility caused by the move- ment of smoke occurs more quickly than does a temperature that is high enough to be debilitating. In all tests, exposure to high levels of CO was never more critical than smoke or temperature.

The effectiveness of the foam suppression system Aqueous Film-Forming Foam (AFFF) that was tested was not dimin- ished by high-velocity longitudinal airflow [4 m/s (787 fpm)]. The time taken for the suppression system to extinguish the fire, with the nozzles located at the ceiling, ranged from 5 s to 75 s. The maximum temperatures experienced at the inlet to the central fans that were located closest to the fire [approx- imately 213 m (700 ft) from the fire] were as follows: 1. 107°C (225°F)—20 MW (68 MBtu/hr) fire 2. 124°C (255°F)—50 MW (171 MBtu/hr) fire 3. 163°C (325°F)—100 MW (341 MBtu/hr) fire. In a road tunnel, smoke management necessitates either direct extraction at the fire location or the generation of a lon- gitudinal velocity in the tunnel that is capable of transporting the smoke and heated gases in the desired direction to a point of extraction or discharge from the tunnel. Without a smoke management system, the direction and rate of movement of the smoke and heated gases are determined by fire size, tunnel grade (if any), pre-fire conditions, and external meteorological conditions. The program report showed that balanced full-transverse ventilation is ineffective in controlling smoke and tempera- tures when fires are above 20 MW (68 MBtu/hr). Being able to effectively control the temperature when fires are below 20 MW (68 MBtu/hr) depends on their locations. However, if the transverse ventilation system is modified to be a two zone system, it can have the capability to control temperature and smoke for a 20 MW (68 MBtu/hr) fire positioned at dif- ferent locations along the length of the tunnel. Runehamar Tunnel Tests The Runehamar Tunnel fire tests were initiated, planned, and performed by the Swedish National Testing and Research Institute from 2001 to 2003 as a part of the Swedish National Research program and in collaboration with the European UPTUN project led by TNO (The Netherlands) (27). (See web-only Appendix E for tests description.) Free-burn fire tests in the Runehamar Tunnel in Norway alarmed the industry with a 200 MW (682 MBtu/hr) HGV fire size and its fast growth, because in the past no one believed in such high values. This led to a change in design HRRs for tunnel fires. In 2008, a third series of tests were run in the Runehamar Tunnel to evaluate the performance of water mist. With ventilation of up to 5 m/s (984 fpm), the water mist system was applied to a 100 m2 (1,076 ft2) diesel pool fire and a 200 MW (682 MBtu/hr) HGV fire. Within a minute, the diesel fire was extinguished. After a minute for the HGV fire, the temperature had dropped below 50°C (122°F), 20 m (66 ft) upstream, and below 280°C (536°F), 32 5 m (16 ft) downstream. A mock-up of a partially filled lique- fied petroleum gas (LPG) tank was tested for exposure and boiling liquid expanding vapor explosion (BLEVE) risk. The water mist system prevented a risk of a BLEVE for the diesel pool fire and for the solid fire if the water mist system was activated before the HRR exceeded 50 MW (171 MBtu/hr). However, if the water mist system activation was delayed until the HRR reached 200 MW (682 MBtu/hr) there was a serious risk of a BLEVE. Measurements were taken of the tempera- ture, CO concentration, and visibility downstream of the fires. It was concluded that tenability was regained within a few minutes of activation of the water mist system. There have been numerous papers discussing and analyz- ing the test results and what allowed the fire to grow to that size. Some questions included: • The type of truck burning (open trucks are not used in the United States). • The tunnel size, which was smaller (narrower) than a typical road tunnel. • Protection of tunnel walls with heat protection material, which does not allow for heat dissipation through the walls, but rather reflects heat from the walls back to the tunnel environment with superimposed heat waves. Results of the tests have been published in the Annex materials of NFPA 502, in ASHRAE, and in other docu- ments impacting mechanical and structural tunnel design in many countries of the world. UPTUN Project Tunnel Tests The HRRs for single passenger cars (small and large) vary from 1.5 to 9 MW (5.1 to 31 MBtu/hr); however, the majority of the tests show HRR values of less than 5 MW (17 MBtu/hr). When two cars are involved, the peak HRR varies between 3.5 and 10 MW (12 and 34 MBtu/hr). There is a substantial variety in the time to reach peak HRR; that is, between 10 and 55 min. It has been shown that the peak HRR increases linearly with the total calorific value of the passenger cars involved in the fire. An analysis of all data available shows that the average increase is about 0.7–0.9 MW/GJ (2.4–3.1 MBtu/hr/GJ). There have only been a few bus fire tests performed. The two tests shown in the Table 6 indicate that the peak HRR is on the order of 30 MW (102 MBtu/hr) and the time to reach peak HRR is less than ten minutes. The highest peak HRRs were obtained for the HGV trailers (single), which were found to be in the range of 13 to 202 MW (44 to 689 MBtu/hr), depending on the fire load. The time to reach peak HRR was in the range of 10 to 20 min. The fire duration was less than one hour for all the HGV trailer tests presented in Table 6. The fire growth rate after reaching 5 MW (17 MBtu/hr) was nearly linear during all the tests carried out

Type of vehicle, model year, test nr. u = longitudinal ventilation m/s Calorific Value (GJ) Peak HRR (Qmax) MW Time to Peak HRR (min) Peak Temperatures in Tunnel Ceiling (°C) Reference [see Ingason (28)] Passenger cars Ford Taurus 1.6, late 70s, Test 1 4 1.5 12 N/A Mangs and Keski- Rahkonen Datsun 160 J Sedan, Late 70s, Test 2 4 1.8 10 N/A Datsun 180 B Sedan, Late 70s, Test 3 4 2 14 N/A Fiat 127, Late 70s, 0.1 m/s N/A 3.6 12 N/A Ingason et al. Renault Espace J11-II, 1988, Test 20, u = 0.5 m/s 7 6 8 480 Steinert Citroën BX, 1986 5 4.3 15 N/A Ship and Spearpoint Austin Maestro, 1982 4 8.5 16 N/A Opel Kadett, 1990, Test 6, u = 1.5 m/s N/A 4.9 11 210 Lemaire et al. Opel Kadett, 1990, Test 7, u = 6 m/s N/A 4.8 38 110 Renault 5, 80s, Test 3 2.1 3.5 10 N/A Joyeux Renault 18, 80s, Test 4 3.1 2.1 29 N/A Small Car, 1995, Test 8 4.1 4.1 26 N/A Large Car, 1995, Test 7 6.7 8.3 25 N/A A/N117.31.31tseT,tnabarT Steinert A/N727.12.32tseT,nitsuA A/N716.483tseT,neortiC Renault Laguna, 1999 13.7 8.9 10 N/A Marlair and Lemaire Two passenger cars Citroen BX + Peugeot 305, 80s, Test 6 8.5 1.7 N/A N/A Joyeux Small Car + Large Car, Test 9 7.9 7.5 13 N/A Large Car + Small Car, Test 10 8.4 8.3 N/A N/A BMW + Renault 5, 80s, Test 5 N/A 10 N/A N/A Polo + Trabant, Test 6 5.4 5.6 29 N/A Steinert Peugeot + Trabant, Test 5 5.6 6.2 40 N/A Citroen + Trabant, Test 7 7.7 7.1 20 N/A Jetta + Ascona, Test 8 10 8.4 55 N/A Three passenger cars Gold + Trabant + Fiesta, Test 4 N/A 8.9 33 N/A Buses A 25–35-year-old, 12-m long Volvo School Bus with 40 Seats, EUREKA 499, u = 0.3 m/s 41 29 8 800 Ingason A Bus Test in the Shimizu Tunnel, u = 3–4 m/s N/A 30 7 303 Kunikane et al. HGV A Trailer Load with Total 10.9 Ton Wood (82%) and Plastic Pallets (18%). Runehamar Test Series, Test 1, u = 3 m/s 240 202 18 1365 Ingason and Loˇnnermark Loˇnnermark Loˇnnermark A Trailer Load with Total 6.8 Ton Wood Pallets (82%) and PUR Mattresses (18%). Runehamar Test Series, Test 2, u = 3 m/s 129 157 14 1282 Ingason and A Leyland DAF 310ATi: HGV Trailer with 2 Tons of Furniture, EUREKA 499, u = 3–6 m/s 87 128 18 970 Grant and Drysdale A Trailer with 8.5 Ton Furniture, Fixtures, and Rubber Tires. Runehamar Test Series, Test 3, u = 3 m/s 152 119 10 1281 Ingason and Loˇnnermark A Trailer Mock-up with 3.1 Ton Corrugated Paper Cartons Filled with Plastic Cups (19%), Runehamar Test Series, Test 4, u = 3 m/s 67 67 14 1305 Ingason and TABLE 6 LARGE-SCALE EXPERIMENTAL DATA RESULTS FROM UPTUN TESTS (continued on next page)

in the Runehamar Tunnel and it varied between 16.4 and 26.3 MW/min (55.9 and 89.7 MBtu/hr/min). The measured ceiling temperatures varied from 110°C to 1365°C (230°F to 2489°F). These temperatures can be com- pared with standardized time–temperature curves for load- bearing design in buildings and underground construction. After one hour of exposure, the temperature exceeded 925°C (1697°F). The results in Table 6 indicate that there is a correlation between high HRR and high temperatures. Ingason has shown that the highest temperatures (>1300°C or 2372°F) are obtained with HRRs larger than 20 MW (68 MBtu/hr) and low ceiling heights (approximately 4 m to 5 m) in com- bination with intermediate ventilation rates. For high HRR, the flames reach the ceiling and the combustion zone where the highest temperatures are usually found. It is located close to the ceiling, even when the longitudinal ventilation deflects the flames. When the longitudinal ventilation rate increases fur- ther, the cooling effects predominate and the temperature drops again. The geometrical shape and size of the fire, the tun- nel cross section (especially the height), and the ventilation rate are thought to be the principal parameters that determine the temperature level at the ceiling. (See web-only Appendix E for additional information.) General Observations on Large-scale Tests Based on Reported Results The recent research programs are based on complete mea- surement systems. They use numerous instrumentations and are organized into networks quite similar to the mesh used in CFD models. One of the characteristics of these experiments is that no access is possible in the fire area. No visual observation is then possible, except when a video camera is installed in that zone. In some cases, operators could be present in the sec- tions located upstream from the fire. This situation cannot provide an overview of the experiment. 34 In these conditions, a large amount of recorded data would be helpful to build interpretations concerning the phenomena developed during the fire. The type of measurement instru- mentation and its location on three-dimensional (3D) mesh appears fundamental for the analysis of tests results. The goal of most of the experiments was not to research the physical relations of the phenomena, but to check specific equipment or materials being sponsored by the vendors. It is difficult to obtain general laws from the full-scale experi- ments; however, general observations under specific condi- tions can be made. This is the result of the relatively low number of experiments performed in each program. For exam- ple, the Japanese tests were partly planned to provide qualita- tive information about the escape routes in different air velocity control conditions. This target does not appear to be compatible with the use of the results in scientific models. Because of the uncertainties on the measurement results, the interpretations generally concluded that the calculated HRR is linked to the method used for its evaluation. The full-scale experiments generally provide interesting qualitative observations. For example, some opacity situa- tions appear clearly as a combination of the HRR, the nature of the burning object (smoke density), and the longitudinal air velocity. The relatively low number of experiments does not lead to general laws or conclusions. (An exception would be the Memorial Tunnel program because of the large num- ber of tests.) These observations might be used as a reference for more specific research using appropriate tools (small- scale or numerical models). In general, the measurements made during the experi- ments can be used as a basis for simulations and particularly for CFD. The qualification of a simulation tool must follow several rules: • Thematic: a reference experiment must deal with fires in tunnels. Cold smoke tests cannot represent fire behavior. HGV A Trailer Load with 72 Wood Pallets. Second Benelux Tests, Test 14, u = 1–2 m/s 19 26 12 600 Lemaire et al. A Trailer Load with 36 Wood Pallets. Second Benelux Tests, Tests 8, 9 and 10, u = 1.5, 5.3, and 5 m/s 10 13, 19 and 16 16, 8, and 8 400, 290, 300 Lemaire et. al. A Simulated Truck Load (STL), EUREKA 499 63 17 15 400 Ingason Source: Ingason (28). N/A = not available. Type of vehicle, model year, test nr. u = longitudinal ventilation m/s Calorific Value (GJ) Peak HRR (Qmax) MW Time to Peak HRR (min) Peak Temperatures in Tunnel Ceiling (°C) Reference [see Ingason (28)] TABLE 6 (continued)

35 • Reliability: the quality of the results must be correct. Appropriate instrumentation shall be used. • Representatively: the measurements have to describe as completely as possible the phenomena that have to be characterized by the numerical simulation. • Adaptability: even if the previous characteristics are satisfied, the reference experiment must be adapted to a comparison with simulation. For example, chaotic behaviors linked to uncontrolled fires such as vehicle fires are not easy to understand and to integrate as boundary conditions. None of the large-scale tests completely meet those require- ments because of the relatively small number of tests with real vehicles. The number of experiments is limited because of the huge costs involved in such programs (about $40 million USD for the Memorial Tunnel program). These costs lead to limiting the duration of the program and, as a consequence, the num- ber of affordable experiments. Most of these tests were performed in abandoned tunnels. For a road application, extrapolations are often necessary because of the reduced cross section and its different shape (e.g., horse shoe instead of rectangular or other shape). Tests in Tunnels Before or Under Operation There is a requirement and a standard practice in most coun- tries for performing tests before a tunnel is opened. In the United States, the typical requirement is to test all the sys- tems and perform a cold smoke test for witnessing the smoke movement. Typically, there are no requirements for hot smoke tests or tests of burning vehicles before commissioning in new U.S. tunnels. Many European countries perform small-size (3–5 MW or 10–17 MBtu/hr fire) hot smoke tests, burning a pan with fuel, while activating the fire life safety systems and simulat- ing emergency response procedures. Tests in tunnels before they are put into operation are generally done with calibrated fires such as fuel pools or wood cribs. Pool fires can be used to obtain steady states, which are needed to measure the combustion rate to evaluate the HRR. There is a substantial amount of information on heptane pool fires. Diesel oil can be used to avoid explosions or to produce more smoke. In France, to be more demonstrative, they usually burn cars in new tunnels before commissioning a tunnel system. Although it is more expensive, it provides a better simulation of an actual fire event, because the HRR is very chaotic and unpredictable. The tunnel ventilation system effect is better characterized when the thermal situation is stabilized in the pool fire tests; therefore, the use of cars as fire loads is rec- ommended after the fire pool tests are done. These tests are generally performed in tunnels before they are put into operation to demonstrate if the smoke extraction system will work correctly if an accidental fire occurs. The recent developments of such tests show that the efficiency of the ventilation is linked both to its quantitative capacity and to the way it is operated. As this second point is never treated by recommendations or regulations, specific developments are necessary to determine optimal reactions adapted to the fire (location, HRR, natural ventilation, and so forth). The second goal of these tests is to show the operators how to react in case of a fire. The tests may be completed with fire department exercises and intervention evaluations. PIARC (21) suggests performing tests before opening the tunnel to establish instructions for fire situations. The sec- ond kind of test, suggested during operation, is used to train operators and fire departments. The tunnel must be closed specifically for these tests. One of the PIARC report recom- mendations is to conduct such tests regularly. Because the HRR is limited, it is possible to observe the phenomena in different zones of the tunnel, even near the fire. These observations may be correlated with the measure- ments (smoke motions compared with temperature fields, backlayering evolution, and stratification downstream of the fire, and so forth). Many tests can be performed in a rather short time. It is estimated that about 20 fires can be studied in one week, con- sidering safety precautions. Instrumentation is limited, but the evolution of these tests tends to increase the number of sensors. Also, the total amount will be limited because this kind of experiment is distinct from research programs; in particular, it will be difficult to characterize the phenomena occurring at large distances from the fire zone. The size of the fire must also be limited because these tests must be nondestructive. Actually, it is necessary to limit the product “Heat release rate × Duration.” Tests involving 20 MW (68 MBtu/hr) sources were performed, but this value is consid- ered an exception. Generally, the test fires do not exceed 5 MW (17 MBtu/hr). During passenger cars tests, peaks of 7 to 8 MW (24 to 27 MBtu/hr) were observed, but they did not last long. The Puymorens and Chamoise Tunnel tests have been based on heptane pool fires (21). Many different steady states have been characterized and these results have been used to determine ventilation requirements. They have also been analyzed from a scientific point of view to determine the gen- eral laws governing smoke motion and other thermodynamic behaviors. For example, during the Chamoise Tunnel tests, it was possible to measure the backlayering distance in each case (Figures 9 and 10). The complete analysis of the various parameters shows that the backlayering distance may be

written as a function of the Richardson number (Ri) and depends on the tunnel characteristics. The Richardson num- ber considers the density of the gases in the plume impact zone under the ceiling. SMALL-SCALE TESTING (PHYSICAL MODELING) Small-scale experiments can be designed to represent a fire in a planned tunnel (see Figure 11). This method is based on similarity laws, which are actually the link between a full- scale situation and the modeled one (21). The objective of such experiments is to represent the phe- nomena that develop during a fire within a tunnel. Compared with full-scale tests, this method allows some savings of time and money and the ability to analyze the phenomena in detail. Such tests are not affected by natural factors such as winds, elevations, and solar radiation, and can be repeated as many times as necessary. One of its goals is also to be demon- strative, because it is possible to visualize smoke. However, 36 there are only a few examples of reduced-scale model appli- cations for tunnel design that can be mentioned (30). One example is a study on smoke stratification stability on a one-third scale model. The Froude scaling enables modeling of thermal effects and smoke backlayering. The fire is modeled using a heptane pool fire and can be characterized by: • Theoretical total HRR calculated from the mass con- sumption of heptane. • Total HRR computed from the oxygen consumption. • Convective HRR with volumetric flow rate estimated by integration of the velocity profile measured down- stream of the fire. The difference between the two total HRRs is combustion efficiency and radiation fraction. Researchers can use small-scale models for scientific rea- sons. If some specific behaviors have to be characterized, the best solution can be to show them using totally controllable methods. Complementary tests may be done with full-scale facilities. The knowledge of the laws obtained with the models is useful in planning full-scale experiments. Small-scale models have been used to characterize the efficiency of ceiling trap doors for smoke extraction or to determine nondimensional laws governing the existence of backlayering. The similarity laws are the fundamental link between the model and the corresponding full-scale situation. If this link is not shown to be strong, the study results cannot be consid- ered as representative of the full-scale situation. Actually, in a more general manner, the validity of the experiments has to be considered as relative to the used similarity law. As a con- sequence, it depends on the small-scale model technique. The situation observed during a fire inside a tunnel appears as the result of an interaction between two major forces: FIGURE 9 Backlayering distance vs. longitudinal air velocity for two heptane pool surfaces [tunnel slope = 0.5 %—Chamoise fire tests (21)]. FIGURE 10 Plabutch Tunnel Fire Test sponsored by Graz University of Technology. FIGURE 11 Small-scale experiments (physical modeling) (29).

37 1. Force induced by natural or mechanical effects. It is characterized by the air velocity obtained upstream of the fire, U. 2. Buoyancy forces developed in the fire plume, which are induced by the gases’ expansion resulting from the high temperature. The fundamental characteristic is given by the density difference between the air and the hot gases, Δρ. To represent the turbulent longitudinal flow, it appears necessary to use the Reynolds number Re: where: Dh represents the hydraulic diameter, and v represents the fluid cinematic viscosity. The effect of buoyancy forces are partially represented by the Froude number, Fr: where g represents the gravity acceleration. The Froude number modified with the density differences represents the gravity effects on fluid motions, resulting in the Richardson number: Other parameters may be used to study phenomena on reduced-scale models. For example, the Grashof number is a combination of the Reynolds and the Richardson numbers: The Reynolds condition is generally limited to checking that the Reynolds numbers in the model are sufficient to ensure the turbulent character of the longitudinal airflow. The thermal exchanges with the walls are difficult to model exactly as they would appear in an actual tunnel. The relation between the backlayering distance, the local slope, the heat release, and the thermal exchanges with the walls has been demonstrated using small-scale models. Den- sity change represents temperature and vertical velocity as the function of burned gases. The fire source can be modeled by a flux mixing a light gas (generally helium) and air or nitrogen. These models cannot represent thermal exchanges with the walls. The isothermal source does not take into account the physics of fires. In real- istic situations, the combustion temperature is related to the vertical velocity. In the experiments, these two parameters are not dependent. Such experiments have been used to character- Gr = ( )( )gD vh3 2 17Δρ ρ ( ) Ri = ( )( )gD Uh 2 16Δρ ρ ( ) Fr = U gDh2 15( ) Re = UD vh ( )14 ize the limits of the existence of backlayering. These experi- ments have been associated with a CFD technique. The good correlation obtained shows that the control of the boundary conditions in the experiments was correct and that they could be correctly described in order to perform numerical simula- tions. It is to be noted that the characterization of these bound- ary conditions for full-scale tests remains a problem. Using a small-scale model to design a tunnel ventilation system may be limited for two primary reasons: • Technical conclusions are relative to the similarity law(s) used. A fire is a complex phenomenon and its represen- tation cannot be limited to one or two global relations. • HRR representation remains an unsolved problem. It is not correct to conclude that the lack of total similarity leads to unrealistic results. For example, the conclusions drawn from small-scale experiments performed in the Channel Tunnel on shuttles have been confirmed later through full-scale tests. The representation of realistic situations with reduced- scale models depends on the number of similarity laws taken into account. As only one parameter is simulated (Froude or Richardson number), the global validity of this kind of study is not accurate. The application of this technique to full-scale situations is not immediate. As an example, the conclusions drawn from the study concerned with trap doors or single- point extraction openings, recently done in France, have been applied to other projects because they provide valuable answers concerning the relative capacities of the various systems; however, absolute results were not used. The second case is the use of small-scale models for re- search. The conclusions of such studies are generally limited to the model studied. The transposition of the established laws to full-scale situations needs reference experiments. Therefore, the interest of these models is to show that general laws can be drawn from the study of specific situations, which also give analytic form for these laws (e.g., existence of backlayering versus source characteristics and longitudinal air velocity.) In general, the validity of a study based on the use of mod- els is directly linked to the interpretation of the similarity law. LARGE-SCALE EXPERIMENTAL FACILITIES Such tests can be considered to be somewhere in between a full-scale road tunnel test and small-scale laboratory tests. An example of such a facility is a laboratory tunnel of Carleton University, located in Almonte, Ontario, Canada, which is used for performing large-scale experiments. The tunnel is 37.5 m (123 ft) long and the cross section is 10 m (32.8 ft) wide and 5.5 m (18 ft) high. The tunnel has a shutter opening [3.8 m wide (12.5 ft) and 4.0 m (13.1 ft) high] and two louvered openings [1.2 m wide (3.9 ft) and 4.5 m (14.8 ft) high] at the east end. Figure 12 is a schematic diagram of the tunnel facility.

This facility was recently used to study the impact of tunnel suppression on tunnel ventilation systems. The absolute cool- ing effect and radiation attenuation were examined by activat- ing the sprinkler system over a propane fire, which generated a constant HRR. The test examined the effectiveness of the lon- gitudinal ventilation system with the sprinkler system active. When the sprinkler system was turned on, some smoke escaped from the tunnel openings; however, overall, the ventilation sys- tem was able to control the smoke. The sprinkler system cooled smoke, caused steam formation, and lowered visibility. With the sprinkler system active, ceiling temperatures upstream of the fire and in the spray section dropped dramatically. It was found that the sprinkler system and ventilation system effec- tively cooled down smoke and reduced the heat flux. The mea- sured heat fluxes showed that the absorption of thermal radiation and transmission of the radiation can be affected by the sprinkler system and air flow in the tunnel. The longitudi- nal air flow in the tunnel was affected by the discharge of water sprays because the air flow velocity was as low as 1 to 2 m/s (197 to 394 fpm). However, the ventilation system was able to control smoke in the tunnel. As the sprinkler system reduced the smoke temperature, it could be expected that the driving force to propagate the smoke decreased, thus enabling the lon- gitudinal ventilation system to prevent backlayering of smoke. GAPS IN FIRE TESTING, MODELING LIMITATIONS, AND COMPUTATIONAL FLUID DYNAMICS VERIFICATIONS The Memorial Tunnel Fire Test program produced a substan- tial amount of valid information and test results for further studies. However, the program used fuel pans to simulate fire. There have been no full-scale fire test programs with real cars, buses, and trucks in the United States. The National Fire Pro- tection Association (NFPA) uses information on HRR from the tests performed in Europe and Japan, but recognizes that the open trucks tested in those countries are not used in the United States. It also recognizes that test conditions did not represent typical road tunnel geometry, but used smaller tunnel sections. 38 There is a need for full-scale fire tests using real vehicles to verify FHRRs with fewer corrections to local conditions. A set of full-scale tests in Europe provided valid information on HRRs from cars and HGVs. Limited information was pro- vided on bus fires and no information on gasoline tanker fires. The UPTUN fire tests did not provide much information on smoke and other gases dissipating from the fire during the tests. Smoke dissipation data were obtained during tests in Japan and information appeared in the PIARC and NFPA 502 docu- ments; however, those tests were outdated and the smoke production rate was removed from the documents. Design engineers are advised to select a material, such as polystyrene, mineral oil, polyurethane foam, or wood cribs to calculate smoke production rate. It was noted that smoke was the leading cause of death. A lack of such information could be considered as a significant gap in fire testing. Some observations made during recent fire events noted that smoke is produced faster than the fire grows. This may be associated with the materials burning first. Modelers typically use a linear relation between the HRR and smoke production rate, which may lead to under- estimates of smoke development during the evacuation phase. Numerical modeling has become a tool of choice for design engineers modeling tunnel fires. Designers need to select appropriate physical models and boundary conditions to model fire events. One of the unknowns is the turbulent model. It has been demonstrated in the past that different turbulence models and different coefficients in those models can lead to different (sometimes opposite) results. Design engineers often uncritically use turbulence models proposed by the CFD pack- ages and some default coefficients with little if any under- standing of the accuracy of their selection. However, there were no road tunnel fire tests that required instrumentation that would allow for the measure of turbulence scale. Therefore, the user inputs the recommended turbulence models and model coefficients, which can lead to incorrect design or speculation on the modeling results. FIGURE 12 Schematic diagram of the laboratory tunnel facility of Carleton University (31).

39 The best way to learn is with actual tests. Commissioning for fire life safety systems is done in other countries by burn- ing vehicles in the tunnel before the tunnel opens to the pub- lic. Cold smoke tests or small fuel pan fire tests do not replace a real vehicle fire. Such tests will allow the testing of the design and all the systems, as well as the training of opera- tors, first responders, and design engineers. Some small-scale fire tests (physical modeling) are an im- portant scientific research tool that needs further development to allow better understanding of the physics involved and to see the final results. Such tests allow for the installation of pre- cise instrumentation and the ability to repeat the tests, while enabling easy changes of the parameters and systems res- ponses, as well as fine tuning the systems before the tunnel is built. It also allows for the checking of CFD models. SUMMARY Fire tests are of vital importance to the understanding of the physics of tunnel fires, understanding the impacts of fires, and verifying calculations, assumptions, computer models, and tunnel design. They are also important for tunnel opera- tors and emergency responders to coordinate the efforts and verify in practice the emergency response plans. Fire tests have been performed and can be classified as: • Tests before the design to develop design methodology. • Tests during the design to verify assumptions and com- puter models. • Tests during commissioning to verify the design and equipment operation. • Tests for training purposes. Important conclusions and recommendations that were determined from full tunnel fire tests included: • Ofenegg Tunnel Test results that raised doubts in sprinkler systems for road tunnels. Important conclu- sions on the danger of delayed sprinkler activation or early deactivation of the sprinkler system were observed. • Zwenberg Tunnel tests strongly supported the benefits of a fully transverse system running in a full extraction mode during a fire once the fire is quickly detected and ventilation mode correctly activated. • PWRI experiments concluded that the stratification of smoke was partially destroyed by longitudinal ventila- tion at 1 m/s (197 fpm) and totally destroyed by longi- tudinal ventilation at 2 m/s (394 fpm). They concluded that the sprinklers had an adverse effect on the tunnel environment by causing a reduction in smoke density near the ceiling and an increase in smoke density in the lower part of the tunnel. • Repparfjord Tunnel fire tests registered that the tempera- tures during most of the vehicle fires reached maximum values of 800°C to 900°C (1472°F to 1652°F). The tem- peratures during the HGV test reached 1300°C (2372°F). • Benelux Tunnel tests concluded that sprinklers reduced temperatures to safe levels upstream and downstream of the fire and also reduced the probability of fire spreading between vehicles. • The Memorial Tunnel Fire Ventilation Test Program performed 91 tests with diesel oil pool fires in an aban- doned 850-m-long road tunnel located in West Vir- ginia, with fire sizes of 10, 20, 50, and 100 MW (34, 68, 172, and 341 MBtu/hr). Diesel oil pool fire tests do not allow making conclusions on among other issues the expected real tunnel fire size, growth rate, smoke gen- eration rate, and real smoke stratification. Tests were performed with various ventilation systems including: – Full-transverse ventilation – Partial transverse – Single-point extraction – Oversized exhaust – Natural ventilation – Longitudinal ventilation with jet fans. Tests concluded that a longitudinal ventilation system employing jet fans is highly effective in managing the direction of the spread of smoke for fire sizes up to 100 MW in a 3.2% grade tunnel, which allowed for its application in the United States. • The Runehamar Tunnel fire tests alarmed the industry with a 200 MW (682 MBtu/hr) HGV fire size and its fast growth. • UPTUN Project tests indicated that there is a correlation between high HRR and high temperatures. The geo- metrical shape and size of the fire, the tunnel cross sec- tion (especially the height), and the ventilation rate are thought to be the principal parameters that determine the temperature level at the ceiling. Most of these tests were performed in abandoned tunnels. Each test was done differently and had its own purpose(s), often driven by the sponsors and vendors. The tests had dif- ferent methodologies and were performed in tunnels of dif- ferent configurations. For a road application, extrapolations are often necessary because of the reduced cross section and its different shape. The full-scale experiments generally provided interesting qualitative observations. The relatively low number of exper- iments does not lead to the creation of general laws. (An exception would be the Memorial Tunnel program, because of the large number of tests conducted.) It appears that the ideal full-scale test is one that can be done in a typical size and shape road tunnel using actual cars and trucks for burning, can perform a large number of experiments, is well-prepared and equipped with the precise instrumentation suitable for the test conditions, and allows for the generalization of the test results on both macro- and micro-levels. The international practice of commissioning tunnel fire life safety equipment and fire fighting procedures using hot

smoke tests and burning actual vehicles in the tunnels needs to be evaluated for future national standards considerations. Small-scale experiments can be designed to represent a fire in a planned tunnel. This method is based on similarity laws, which are actually the link between the full-scale sit- uation and the modeled one. Compared with full-scale tests, this method allows for some savings of time and money and for analyzing the phenomena in detail. Such tests are not affected by natural factors such as winds, elevations, and solar radiation, and can be repeated as many times as necessary. Using a small-scale model to design a tunnel ventilation system may be not be practical for two main reasons: 40 • Technical conclusions are relative to the similarity law(s) used. A fire is a complex phenomenon and its represen- tation cannot be limited to one or two global relations. • HRR representation remains an unsolved problem. Large-scale tests can be considered to be somewhere between a full-scale road tunnel test and small-scale labora- tory tests. Table 7 summarizes benefits for research, design and operation of tests and models, and their advantages and disadvantages. There have been no full-scale fire test programs with real cars, buses, and trucks in the United States. There is a need for full-scale fire tests using real vehicles in real road tunnels to verify FHRRs with fewer corrections to local conditions. TABLE 7 FIRE TESTS FOR RESEARCHES, DESIGNERS AND OPERATORS noitarepOrofesUngiseDrofesUhcraeseRrofesUsnaeM Full-scale Fire Test Programs Advantages: - Direct interpretation - Complete results Disadvantages: - Cost - Limited number of tests Conclusions: - Well suited Advantages: - Direct interpretation - Possibility of using real road vehicles Disadvantages: - Cost - Limited number of tests - Geometry of the test facility Conclusions: - This solution depends on the importance and specific problems of the project (e.g., Memorial Tunnel) Advantages: - Direct interpretation Disadvantages: - Cost - Limited number of tests Conclusions: - Unrealistic if not associated with other objectives Tunnel Fire Tests Before or Under Operation (aimed at optimizing ventilation responses in fire event) Advantages: - Partial results with full- scale facilities - Numerous different situations Disadvantages: - Lack of information due to the limited number of sensors Conclusions: - Useful but partial results Advantages: - Accumulation of experience useful to choose a system - Test performed with real ventilation systems Disadvantages: - Limited number of tests Conclusions: - Useful Advantages: - Shows operators how the ventilation reacts - Fire departments are very interested in expected situation Disadvantages: - No operation possible during the tests Conclusions: - Well suited Tunnel Fire Tests Before or Under Operation (aimed at operators and fire department training) Advantages: - Visual observations possible Disadvantages: - Lack of information due to the absence of sensors Conclusions: - Not suited Advantages: - Test performed with real ventilation systems Disadvantages: - Limited analysis due to the lack of measurements Conclusions: - Not well suited Advantages: - Representative situation Disadvantages: - No operation possible during the tests Conclusions: - Well suited Reduced-scale Models Advantages: - Many tests possible - Possibility of studying global laws governing specific situations Disadvantages: - Needs full-scale reference tests for transposition to real situations Conclusions: - Useful method for research Advantages: - Cost lower than full-scale tests. Disadvantages: - Linked to the limitations induced by the similarity laws Conclusions: - Very difficult to conclude that the results are representative of full-scale situations Advantages: - Cost Disadvantages: - Linked to the limitations induced by the similarity laws - No respect of time basis Conclusions: - Possibly unrealistic but demonstrative

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 415: Design Fires in Road Tunnels information on the state of the practice of design fires in road tunnels, focusing on tunnel fire dynamics and the means of fire management for design guidance.

Note: On September 20, 2011, the following errata was released related to NCHRP Synthesis 415. The electronic version of the publicaiton was changed to reflect the corrections.

On pages 106 and 107, an incorrect reference was cited. In the final paragraph on page 106, the last sentence should read: One study came to the conclusion that, although some minimum water application rates would achieve a certain objective, a marginally higher rate would not necessarily improve the situation (79). The figure caption for Figure 35 at the bottom of page 107 should read: FIGURE 35 NFPA 13, NFPA 15, and other International Water Application Rates (79).

The added reference is as follows:

79. Harris, K., “Water Application Rates for Fixed Fire Fighting Systems in Road Tunnels,” Proceedings from the Fourth International Symposium on Tunnel Safety and Security, A. Lönnermark and H. Ingason, Eds., Frankfurt am Main, Germany, Mar. 17–19, 2010.

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