Hydrogen Release Deflagrations in a Sub-Scale Vehicle Tunnel

Transcription

1 WHEC 1 / 13-1 June Lyon France Hydrogen Release Deflagrations in a Sub-Scale Vehicle Tunnel Yasukazu Sato a, Erik Merilo b, Mark Groethe b, James Colton b, Seiki Chiba c, Hiroyuki Iwabuchi a, Yuki Ishimoto a a Research and Development Department The Institute of Applied Energy 1-,Nishishinbashi 1-Chome Minato-ku Tokyo 15-3 Japan ysato@iae.or.jp iwabuchi@iae.or.jp ishimoto@iae.or.jp b SRI International, Poulter Laboratory 333 Ravenswood Avenue Menlo Park, CA, 95 USA erik.merilo@sri.com mark.groethe@sri.com james.colton@sri.com c SRI International Park Side House F, Ichibancho, Chiyoda-ku Tokyo 1- Japan schiba@sri.co.jp ABSTRACT: An important issue concerning the safe use of hydrogen powered fuel cell vehicles is the possibility of accidents occurring within a tunnel. Such accidents might result in the release and deflagration of hydrogen from a vehicle s storage tanks or possibly from a hydrogen transport vehicle such as a tube trailer or tank car on a freight train. A total of ten experiments have been performed to examine the effects of confined deflagrations that could occur after a release of hydrogen in a tunnel. Release rates were scaled to match possible leak scenarios from fuel cell vehicles and hydrogen transports. Possible enhancement of the deflagration due to obstacles in the tunnel was studied by performing experiments with scale model buses in the tunnel. A system of evacuated sampling bottles was used to measure hydrogen concentration throughout the tunnel prior to ignition, and at various times during the release. All releases produced lean hydrogen concentrations. The releases that were ignited produced overpressures below.3 kpa. KEYWORDS : hydrogen, deflagration, tunnel, concentration, overpressure. Introduction SRI International has developed a sub-scale vehicle tunnel testing facility in order to address critical safety issues involved with the use of fuel cell vehicles and hydrogen transports in tunnels. The Institute of Applied Energy (IAE) and SRI International performed this work for the New Energy and Industrial Technology Development Organization (NEDO) as part of the Development for Safe Utilization and Infrastructure of Hydrogen program. IAE and SRI collaborated closely on planning the experiments. The experiments were performed by SRI in the tunnel testing facility at the SRI test site. These experiments have been carried out in order to obtain fundamental data on hydrogen explosions. Specifically, the experiments examine the characteristics of confined hydrogen releases, explosions, and possible enhancement of the flame front propagation due to obstacles in the flow. The goal is to enable better prediction of hydrogen explosions, improve capabilities to perform risk assessments and develop mitigation techniques. The data will be used to validate computer codes such as AutoReaGas used by Mitsubishi Heavy Industries (MHI), Ltd. The in-tunnel release accident scenario is a particularly hazardous situation for three reasons. First, it provides an environment where a release of hydrogen can be partially confined, allowing concentration to 1/11

2 WHEC 1 / 13-1 June Lyon France build up to a more highly flammable mixture. Second, should ignition occur, the confinement of the deflagration causes enhancement of the combustion, increases flame front velocity, and produces high, directed overpressures. Third, the presence of vehicles in the tunnel can act as turbulence-generating obstacles that could further enhance the deflagration and increase the flame front velocity. The fact that this situation can occur in a tunnel densely packed with vehicles full of people only adds to the risk. In some situations it may be possible for the deflagration to transition to a detonation. It is important to investigate what type of obstacles and blockage ratios represent a real hazard so that appropriate codes and standards and mitigation techniques can be developed in order to reduce the risk to the general public. Two different types of tunnel experiments have been preformed. In the first stage of tunnel experiments a series of tests were preformed to examine the effects of homogeneous gas mixture deflagrations [1]. These tests were intended to represent an actual tunnel design in Japan and do not represent a worst case scenario in terms of blockage ratio. The data from these experiments have been compared to the data form deflagration experiments of homogeneous hydrogen air mixtures and natural gas and air mixtures, which were conducted in the free-field [,3]. For the homogeneous experiments in the tunnel the pressure and impulse were nearly constant over the tunnel length. The results showed a significant enhancement of the deflagration over equivalent explosions in the free-field. For a lean hydrogen mixture (9.5%) the pressure pulses produced were too low for the sensors to detect. The presence of vehicle models in the tunnel did not enhance the combustion because of the small blockage ratio (.3). In the second stage of tunnel testing ten experiments have been performed in order to study potential hydrogen release accident scenarios in a tunnel. It is these release experiments that this paper will address. For these experiments four different types of leaks were considered. These include releases from a fuel cell vehicle, fuel cell bus, one bottle on a hydrogen transport, and bottles on a hydrogen transport. Table 1 lists the types of releases and gives details on the full scale release scenarios. Scenario Table 1. Full scale release scenarios Tank Size Initial Pressure Hole Diameter Release Duration Quantity Released (Vehicle Type) (m 3 NPT) (MPa) (mm) (Seconds) (m 3 NPT) Fuel Cell Vehicle Fuel Cell Bus (1 bottle) ( bottles) Facility and Procedures The experiments were performed in a model vehicle tunnel that measures. m in diameter by 7.5 m long and has a cross-sectional area of 3.7 m. The tunnel is approximately 1/5 of full scale. Figure 1 shows a view of the tunnel and its cross-section. Figure 1. Tunnel facility and cross-sectional view. /11

3 WHEC 1 / 13-1 June Lyon France Air flow Air flow - range + range - range + range - range + range Fan Fan Figure. Configurations for tunnel release experiments. The hydrogen releases were performed at the midpoint of the tunnel, with the release point located about.15 m off the road surface pointing towards the roof of the tunnel. Figure shows a schematic of the test configurations. The hydrogen gas was supplied by.3 m 3 tanks. The hydrogen passed from the tanks, into a manifold that combined the flow into a single stainless steel tube that passed through the tunnel wall. At the end of the tube there was a circular orifice of fixed size. The releases were designed to match scaled release profiles of accident scenarios that were calculated by MHI and are detailed in Table 1. The release profiles were controlled by varying orifice size, the total tank volume (single or multiple.3-m3 tanks) and the initial tank pressure. During the releases different ventilation rates were used in the tunnel to study how hydrogen concentrations were affected. The tunnel was ventilated by four ducted fans located at the outlet end of the tunnel. By varying the fan speeds the ventilation rate was controlled. The flow velocity in the tunnel was measured using an Extech model 713 hot wire thermo-anemometer located at the tunnel midpoint in the center of the flow. For the test cases for which there was no ventilation in the tunnel, steps were taken in order to minimize the air flow through the tunnel. For the short duration tests, lasting less than one minute, one end of the tunnel was completely covered with plastic. The plastic insured that there was no flow through the tunnel and the hydrogen distribution was not effected by the covered end because there was not enough time for the gas to reach the end of the tunnel. Figure 3. Tunnel with and without bus models The long duration release experiments lasted 1 minutes. Covering one end of the tunnel for these releases would have affected the hydrogen concentration because the mixture would not have been able to escape from the covered end. In an effort to produce an unventilated tunnel environment while still allowing the hydrogen air mixture to exhaust from each end of the tunnel, one end of the tunnel was covered with a perforated plastic. The purpose of the perforated end was to add a significant flow restriction to minimize the 3/11

4 WHEC 1 / 13-1 June Lyon France air flow velocity through the tunnel while still allowing the hydrogen air mixture to leak out both ends of the tunnel. The perforated plastic had small holes about 3mm in diameter distributed on a grid square grid of about mm over the entire surface. In addition to the small holes, larger flaps were also cut into the covered end at various locations to allow the mixture to escape. Experiments were conducted with an empty tunnel and in one case bus models were used as obstacles to study possible enhancement of the deflagration. The bus models were 1/5 scale and measured 1 mm in length, 5 mm in width, and 7 mm in height. For the experiment with the bus models a total of four were used. About 1 m from each side of the release point two bus models were located side by side in a configuration that represented bus traffic on both sides of the road. In this configuration the blockage ratio of the tunnel was.1. Figure 3 shows the tunnel with the bus models in position. For the in-tunnel release tests, a system of evacuated sampling bottles was used to measure hydrogen concentration throughout the tunnel. Samples were captured at 1 locations three different times during the duration of the release, prior to ignition. Samples were captured about.5 m below the roof of the tunnel and distributed along the length of the tunnel based on the type and duration of release. For ventilated cases samples were only taken down stream of the release. The sampling system is shown in Figure and consists of an evacuated one-liter lecture bottle connected through tubing to the sampling port at valve 1. Remotely operated solenoid valves were used to control the sampling system and a manual ball valve on the lecture bottle allowed it to be removed from the system for analysis. A vacuum pump was used to evacuate the system before the test. Pressure readout H sensor Hydrogen readout Pressure sensor Valve Sample H & air Manifold Valve Vacuum pump Sampling Setup Measurement Analysis Setup Figure. Gas sampling system and the measurement of the hydrogen concentration in the sample To sample the hydrogen concentration, valve 1 was opened, drawing in the gas mixture in the vicinity of the port and into the lecture bottle. Valve 1 was then closed to isolate the lecture bottle. After the test the manual ball valve on the lecture bottles were closed, and they were removed for analysis. Figure shows the setup for analysis. The lecture bottle was attached to the manifold. A vacuum pump was used to remove the air from the interconnecting tubing and the chamber that contains the hydrogen sensor. The chamber volume was minimized so that when the manual ball valve was opened on the lecture bottle, the pressure drop was very small. A Kulite XTM-19-5A absolute piezoresistive pressure sensor records the pressure in the chamber, and this was used to correct the reading obtained from the hydrogen sensor. Multiple sparks on the roof of the tunnel were used in an attempt to ignite the mixture after the release. Between five and seven standard DuPont bridge wires were distributed across the roof of the tunnel. A single bridge wire was fired first by a capacitive discharge unit (CDU) in the location were it was thought the mixture would have the highest concentration. After.5 seconds the remaining bridge wires were fired with a second CDU. The total energy available from each of the CDUs was about joules. After 1 second an Invensys model number U-73 electronic spark ignition module was turned on. When activated spark ignition module produces 15 millijoule sparks at a -cycle. The module was left on for about 1 seconds. /11

5 WHEC 1 / 13-1 June Lyon France The module was located either directly above the release point or slightly down stream from the release point in the ventilated tests. Pressure within the tunnel was measured by 1 pressure transducers mounted flush on the side wall along the entire length of the tunnel. For these measurements, PCB Piezotronics quartz pressure transducers, models 1133A3 and 11M33, were used. Four free-field pressure transducers were also used to measure the pressure just outside the tunnel. On each end, one PCB quartz pressure transducer, model 11M33, was mounted flush in the ground and one PCB pencil probe, model 137A3, was mounted about.75 m above the ground. Medtherm fast response coaxial thermocouples model TCS-1-E-1.-NI-GGSZ-A1- were used to measure the time of arrival (TOA) of the flame front in the tunnel. The thermocouples were located on the roof of the tunnel on each side of the primary bridge wire. All experiments were recorded with standard and infrared video cameras. Test Results Ten tests were conducted to study four different types of accident scenarios with different tunnel conditions. Table gives details on the ten tests that were performed. Table. Test Details Test Scenario Ventilation Hydrogen Released Duration Obstacles (vehicle type) (m/s) (m3 NPT) (seconds) FCV-1 Fuel Cell Vehicle No.3 7. None FCB-1 Fuel Cell Bus No None FCB- Fuel Cell Bus No None FCB-3 Fuel Cell Bus None HTB-1 (1 bottle) None HT-1 ( bottles) No None HT- ( bottles) No Bus Models HT-3 ( bottles) None HT- ( bottles) None HT-5 ( bottles) constant release rate None Test FCV-1 simulated a scaled release from a fuel cell vehicle in a tunnel with no ventilation. The release was preformed for 7. seconds and a total.3 m 3 NTP of hydrogen was released. Figure 5 shows the hydrogen release rate and the hydrogen concentrations on each side of the release point in the tunnel. Concentration samples were taken from 1 to 3 seconds, 3 to 5 seconds, and 5 to 7 seconds after the start of the release. After 7. seconds the release was stopped and the bridge wires were fired in sequence in an attempt to ignite the hydrogen. For this test no ignition occurred. The highest hydrogen concentration before ignition was 5. % directly over the release point. The maximum measured concentration during the release was.3 % directly over the release point captured between 3 and 5 seconds. 5/11

6 WHEC 1 / 13-1 June Lyon France Sample 1 Sample Figure 5. Release rate and hydrogen concentrations for Test FCV-1. Test FCB-1 simulated a scaled release from a fuel cell bus with no ventilation in tunnel. The release was performed for 3.9 seconds and a total of 1.73 m 3 NPT of hydrogen was released. Figure shows the hydrogen release rate and concentrations for Test FCB-1. Samples were captured 1 to 13 seconds, to 3 seconds, and 31 to 3 seconds after the release. The maximum hydrogen concentration before attempting to ignite the mixture was.5% directly over the release point. For this release no ignition occurred. The maximum concentration measured during the test was 9.5% directly over the release point captured between and 3 seconds after the start of the release. Sample Figure. Release rate and hydrogen concentrations for Test FCB-1. Sample Test FCB- was the same release as for Test FCB-1, the difference was that for Test FCB- the hydrogen release was left on when the bridge wires were fired to ignite the mixture. For Test FCB- a total of 1.79 m3 NPT was released over 35.1 seconds. The concentrations measured for Test FCB- are very similar to those measured during Test FCB-1 with a maximum concentration before ignition of 9.%. For this case the mixture ignited and the infrared video showed the flame propagated down the release jet. As a result of the jet igniting an overpressure was generated in the tunnel. Figure 7 shows pressure and impulse waveforms from the test. A peak overpressure of about. kpa was produced by the deflagration and remained relatively constant throughout the tunnel. The impulse was about. kpa-s and also remained relatively constant. /11

7 WHEC 1 / 13-1 June Lyon France Figure 7. Pressure and impulse waveforms for Test FCB- referenced to ignition time. For Test FCB-3 the same release was preformed as was in Test FCB-1, representing a release from a fuel cell bus. An air flow of.1 m/s was ventilating the tunnel. Figure shows a comparison of hydrogen concentrations downstream from the release point at different times during the release. The results show a small reduction in the maximum hydrogen concentration above the release point. The overall concentration profile shows little change between the ventilated and unventilated cases. For Test FCB-3 the maximum concentration measured during the release was.%. Before bridge wires were fired to ignite the mixture the maximum concentration was 7.5%. The infrared video showed that the hydrogen in the tunnel ignited. Thermocouples on the roof of the tunnel indicate that the mixture was ignited when the first bridge wire was fired at a location 3 m downstream from the release point. The thermocouple data indicates that the flame front propagated at a velocity of 1. m/s both upstream and downstream from the ignition point seconds.1 m/s Sample -3 seconds.1 m/s seconds Figure. Hydrogen concentrations for Test FCB-1 and Test FCB-3..1 m/s Test HTB-1 represented a scaled release from a single bottle on a hydrogen transport. For this test the tunnel was ventilated with an air flow of. m/s. Figure 9 shows the release rate and the concentrations down stream from the release point in the tunnel. The release lasted a total of 7.9 seconds and. m 3 NPT of hydrogen was released. The maximum hydrogen concentration of 9.% was measured just before attempting to ignite the mixture. For Test HTB-1 the resulting mixture did not ignite. Sample 1 Sample Figure 9. Release rate and hydrogen concentrations for Test HTB-1 7/11

8 WHEC 1 / 13-1 June Lyon France Test HT-1 simulated a hydrogen release from a hydrogen transport with no ventilation in the tunnel. The release was preformed for seconds and a total of 1.95 m 3 NPT of hydrogen was released. Figure 1 shows the hydrogen release rate and the concentrations in the tunnel. Samples were captured from to 3 seconds, to 3 seconds and 591 to 59 seconds after the release. The concentration distribution in Figure 1 is not symmetric about the release point and the samples captured after seconds show the concentration increasing on one side of the tunnel. This asymmetry was likely due to the fact that for the unventilated case the air flow velocity in the tunnel (which was below the measurement capability of the gauge) was not completely zero. A small amount of flow could occur in the tunnel due to pressure differentials between the ends of the tunnel and thermal gradients in the tunnel. During a long duration release the effect of a small flow velocity will become more pronounced. The maximum concentration before attempting ignition was 7.% directly above the release point. The maximum hydrogen concentration measured during the release was.% directly above the release point to 3 seconds after the release started. For this test case both the standard video and the IR video showed ignition occurred in the tunnel. Thermocouples in the tunnel showed that ignition occurred directly over the release point when the first bridge wire was fired. A flame front velocity of 3.9 m/s was measured by the thermocouples in the tunnel. A small pressure pulse of about. kpa was distinguishable on some pressure transducers. Figure 11 shows pressure and impulse waveforms. Sample Figure 1. Release rate and hydrogen concentrations for Test HT-1. Sample Figure 11. Pressure and impulse waveforms for Test HT-1 referenced to ignition time. For Test HT- four bus models were in the tunnel with two side by side on each side of the release point. The release was the same as the release preformed in Test HT-1 and there was no ventilation. The concentrations in the tunnel were very similar to the concentrations in Test HT-1 with the peak concentration over the release point being slightly higher for the case with buses. The maximum concentration before ignition was.% located directly over the release point and the maximum concentration measured during the release was 9.5% and the second mark. For Test HT- the resulting mixture ignited however No pressure pulse was distinguishable in the pressure transducer data. Thermocouples in the tunnel show that ignition occurred directly over the release point when the first bridge wire was fired. The flame front velocity was measured to be.9 m/s and. m/s in opposite directions at the top of the tunnel. Test HT-3 and Test HT- were performed with the same release rate as Test HT-1 representing a scaled release from a hydrogen transport. For Test HT-3 and Test HT- the tunnel ventilation rate were.5 m/s and.3 m/s respectively. Figure 1 shows the down stream hydrogen concentrations. The results show a reduction in the maximum hydrogen concentration located directly over the release point. For Test HT-3 the maximum hydrogen concentration measured was 7.%, captured between and 3 seconds and the /11

9 WHEC 1 / 13-1 June Lyon France maximum concentration before attempting to ignite the release was 5.5%. For Test HT- the maximum concentration of 5.7% hydrogen was measured between and 3 seconds. Before attempting to ignite the release the maximum hydrogen concentration in the tunnel for Test HT- was.7%. All three releases look relatively similar after seconds. After seconds there is a substantial difference between the three tests. Part of this is due to the fact that the unventilated tests had a tendency to have higher concentrations build up on one side of the tunnel. For Test HT- the entire downstream section of the tunnel was below the lower flammability limit of hydrogen after seconds of the release. At 591 seconds all of the downstream hydrogen concentrations are below the lower flammability limit for both of the ventilated tests. The results show that over a long period of time the ventilation was able to reduce hydrogen concentrations. However for a short duration the ventilation had little effect on the hydrogen concentrations. For both Test HT-3 and Test HT- the mixture did not ignite. 1-3 seconds.5 m/s.3 m/s 1 Sample -3 seconds m/s.3 m/s seconds.5 m/s.3 m/s Figure 1. Hydrogen concentrations for Test HT-1, Test HT-3 and Test HT-. Test HT-5 was performed with a constant release rate of.7 m 3 NPT/s with the tunnel ventilated at. m/s. The release was performed for seconds and a total 15. m 3 of hydrogen was released Figure 13 shows the hydrogen release rate and the hydrogen concentrations downstream from the release point. The results indicate that even with ventilation the concentration at the top of the tunnel changed little with time. Infrared video and thermocouples in the tunnel showed that the hydrogen mixture ignited. Thermocouple data showed that the flame propagated in the downstream direction at about. m/s. No flame was detected in the upstream direction. Any overpressure that were produced by the deflagration were bellow the sensitivity of the gauge. 1 Sample Figure 13. Release rate and hydrogen concentrations for Test HT-5. Discussion For the release tests performed in this series of experiments the highest concentration was always directly above the release point, even when there was ventilation in the tunnel. This was likely due to the fact that the release was directed towards the roof of the tunnel. The velocity of the hydrogen gas leaving the orifice in the vertical direction was very high relative to the air flow in the horizontal direction. This allowed for only a small amount of horizontal displacement of the hydrogen gas before it reached the roof. If the release jet was in a different orientation it is likely that the ventilation would play a bigger role in moving the location of maximum concentration in the downstream direction. When comparing the ventilated and non-ventilated tests the concentration data indicates that there was a slight reduction in the maximum hydrogen concentrations for the ventilated tests. This indicates that the ventilation should be able to reduce the chances of ignition occurring. While the ventilation appears to have 9/11

10 WHEC 1 / 13-1 June Lyon France better mixed the concentrations at the location of maximum concentration it was not effective at reducing the hydrogen concentration in the short time frame (less then seconds). The overall hydrogen concentration profile changed little in the short time frame and the reduction in maximum concentrations were not very big. This would indicate that higher ventilation rates are necessary to rapidly reduce the hydrogen concentration to a lean mixture. For the long duration tests (595 seconds) the highest ventilation rate, Test HT-, was able to reduce the hydrogen concentration in the tunnel during the release. In this case the reduction was measured after seconds. At the end of the test the hydrogen concentration downstream from the release point was all below the lowered flammability limit. Ignition occurred somewhat inconsistently with regards to hydrogen concentration. In some cases tests with similar concentration profile had one test ignite and not the either. For the Fuel Cell Bus experiments with relatively similar concentrations, the ventilated case ignited while the unventilated case did not. Test HTB-1, with a maximum concentration of 9.% did not ignite while test HT-5 with a concentration of.% did ignite. These results may indicate that there is some difficulty in igniting lean mixtures. The results may also be a result of a dependence on the time after the release was completed to when it was ignited. The time of attempted ignition was not precisely controlled for these experiments because a pneumatic valve was used to control the flow of hydrogen and there was some delay in its actuation. Ignition was attempted within one second after the release was stopped. In some case the ignition was attempted within 1 ms and in other cases it was attempted as late as a second after the completion of the release. In general some of the cases that did not ignite had later attempted ignition times. This may indicate the there is only a short time frame for which the hydrogen concentration levels stay with in a flammable concentration level that it is possible to ignite. It is possible that when the release is stopped the hydrogen concentrations rapidly diffused to concentration that was no longer flammable. This would means that if it were possible to stop a leak, the amount of time required for the mixture to drop bellow flammable limits could be small due to the high diffusivity of hydrogen. More experiments would be required to examine this phenomenon. For this set of experiments the overpressures produced in the tunnel were all very small. Of the ten experiments preformed only five ignited, and of these five only three produced measurable overpressures. This is due to the fact that all of the accidents scenarios examined in this series of tests produced lean mixtures. The highest overpressures were measured in Test FCB- where the hydrogen jet was ignited and the overpressures produced were about. kpa. Overpressures of this magnitude are not a threat to people or property. The presence of vehicles in the tunnel did not affect the overpressures generated by the deflagration. However the blockage ration was small and the resulting deflagrations produced very little overpressure. The results indicate that in a tunnel of this size with the release scenarios that were examined, the greatest risk of overpressure is from the ignition of the hydrogen jet. For these accident scenarios the greatest risk to people and property would be from the flame and not the overpressure. This does not mean that greater overpressures will not be produced in the tunnel; it only means that for these specific scenarios the overpressures were not a threat. For tunnels with higher blockage ratios there could be significant risk associated with the turbulent enhancement of the deflagration. Accidents that result in a catastrophic release of hydrogen due to the puncture of the hydrogen tank could produce significant overpressures and need to be studied in the future. Summary and Conclusions Ten experiments were performed to simulate hydrogen releases from fuel cell vehicles, fuel cell buses, and hydrogen transports. Hydrogen concentration samples taken during the release experiments showed that the maximum hydrogen concentration was located directly above the release point for both the ventilated and unventilated experiments. This was probably due to the orientation of the release and the high velocity of the hydrogen jet. Moving away from the nozzle the hydrogen concentration rapidly decreased. Ventilating the tunnel was show to reduce the maximum hydrogen concentration over the release point by a small amount. The ventilation rates that were tested did not have much effect on the overall concentration profile in the tunnel for release durations of less than seconds. For the releases that lasted 595 seconds ventilation was able to reduce the hydrogen concentration in the tunnel. This result suggests that higher ventilation rate may be needed to reduce the hydrogen concentration in the tunnel more quickly. For the ten tests ignition occurred in only five cases. For the hydrogen transport scenarios ventilation appears to have successfully prevented the ignition of the hydrogen mixture. For the fuel cell bus scenario the ventilation did not mitigate the risk of ignition. All of the release scenarios that were studied resulted in lean mixtures. The overpressure that resulted from the confined deflagrations were all very low and did not represent a risk to people or property. The highest overpressure was generated when the hydrogen jet was ignited in the fuel cell bus release scenario. This deflagration resulted in overpressures of about. kpa that were relatively constant throughout the tunnel. The next highest overpressure was produced in the hydrogen transport release scenario with no ventilation. In this case the overpressures generated were only about. kpa. Most of the remaining deflagrations produced overpressures that were below the sensitivity of the gauges. 1/11

11 WHEC 1 / 13-1 June Lyon France The presence of obstacles in the release experiment did not enhance the deflagration; however the overpressures were too small to be an effective measure for comparison. These results show that proper ventilation of a tunnel could reduce the hazards associated with a hydrogen release. Acknowledgement These studies were administered through NEDO as part of the Development for Safe Utilization and Infrastructure of Hydrogen program with funding from the Agency of National Resources and Energy (ANRE) in the Ministry of Economy, Trade and Industry (METI) of Japan References: 1. Y. Sato, E. Merilo, M. Groethe, J. Colton, S. Chiba, H. Iwabuchi: Homogeneous Hydrogen Deflagrations In A Sub-scale Vehicle Tunnel, National Hydrogen Association Annual Hydrogen Conference, March 15,. M. A. Groethe, J. D. Colton, S. A. Chiba, Y. Sato: Hydrogen Deflagration at Large Scale, 15th World Hydrogen Energy Conference, June,. 3. M. Groethe, E. Merilo, J. Colton, S. Chiba, Y. Sato, H. Iwabuchi: Large-scale Hydrogen Deflagrations and Detonations, International Journal of Hydrogen Energy, 31, (), in press. 11/11