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Appropriate emergency response information is required for first responder before hydrogen fuel cell vehicles will become widespread. This paper investigates experimentally the hydrogen dispersion in the vicinity of a vehicle which accidentally releases hydrogen horizontally with a single volumetric flow of 2000 NL/min in the under-floor section while varying cross and frontal wind effects. This hydrogen flow rate represents normally a full throttle power condition. Forced wind was about maximum 2 m/s. The results indicated that the windward side of the vehicle was safe but that there were chiefly two areas posing risks of fire by hydrogen ignition. One was the leeward side of the vehicle's underbody where a larger region of flammable hydrogen dispersion existed in light wind than in windless conditions. The other was the area around the hydrogen leakage point where most of the leaked hydrogen remained undiffused in an environment with a wind of no stronger than 2 m/s.

Hydrogen concentration during combustion in a confined space with a ceiling was investigated. The results indicated that steady-state hydrogen concentration was highest at the ceiling surface for all hydrogen flow rates. When hydrogen concentration was 10-20%, weak flame propagation occurred at the ceiling surface, with the most easily burnable spots being dented areas such as seams, pores and creases on the ceiling surface. The unstable and limited nature of flame propagation at the ceiling surface was attributed to the relationship between temperature and hydrogen concentration in a confined space.

To investigate the events that could arise when fighting fires in vehicles with carbon fiber reinforced plastic (CFRP) hydrogen storage cylinders, we conducted experiments to examine whether a hydrogen jet diffusion flame caused by activation of the pressure relief device (PRD) can be extinguished and how spraying water influences the cylinder and PRD. The experiments clarified that the hydrogen jet flame cannot be extinguished easily with water or dry powder extinguishers and that spraying water during activation of the PRD may result in closure of the PRD, but is useful for maintaining the strength of CFRP composite cylinders for vehicles.

The environmental temperature where vehicles are used varies significantly by region and season, so this study investigated the influence of environmental temperature on the fatigue life of compressed hydrogen tanks for vehicles (Type 3). Pressure-cycle tests with varying environmental temperature were conducted on tanks until the tank was failed. Results indicated that fatigue life decreased in low-temperature environments and improved in high-temperature environments. We investigated the cause of such results using the strains inside and outside the tank and other indexes and found that the effect of autofrettage varied as environmental temperature changed, due to the difference between the thermal expansion rate of CFRP and that of aluminum alloy. Thus, we concluded that fatigue life changed according to changes in environmental temperature.

In this study, hydrogen was leaked using a nozzle that simulated an actual leak port (with varied materials and diameters), and the possibility of ignition was verified to collect data useful for establishing standards for the allowable flow rate of hydrogen leakage on receptacle. With the flow rate of a hydrogen leak set at 250 mL/h(NTP) (hereinafter mL/h is NTP condition) or less, ignition of leaked hydrogen with an electric spark and a small methane-fueled flame was attempted. The results confirmed that ignition of 200 mL/h of hydrogen was not achieved under tested conditions. In some cases, hydrogen at a flow rate of 250 mL/h was ignited. Tissue paper placed in contact with the flame at a flow rate of 250 mL/h combusted, resulting the flame went out almost immediately. Therefore, it was determined that a hydrogen leak at approximately 200 mL/h that occurred in this test is a very low possibility of ignition or spreading.

If a compressed hydrogen tank for vehicles is filled with hydrogen gas more quickly, the gas temperature in the tank will increase. In this study, we conducted hydrogen gas filling tests using the TYPE 3 and TYPE 4 tanks. During the tests, we measured the temperature of the internal liner surface and investigated its relationship with the gas temperature in the tank. We found that the gas temperature in the upper portion of the TYPE 4 tank rose locally during filling and that the temperature of the internal liner surface near that area also rose, resulting in a temperature higher than the gas temperature at the center of the tank. To keep the maximum temperature in the tank below the designed temperature (85°C) during filling and examine the representative tank internal temperatures, it is important to examine filling methods that can suppress local rises of tank internal temperature.

Fuel cell vehicles represent a new system, and their safety has not yet been fully proved comparing with present automobile. Thorough safety evaluation is especially needed for the fuel system, which uses hydrogen as fuel, and the electric system, which uses a lot of electricity. The fuel cell stacks that are to be loaded on fuel cell vehicles generate electricity by reacting hydrogen and oxygen through electrolytic polymer membranes which is very thin. The safety of the fuel and electric systems should also be assessed for any abnormality that may be caused by electrolytic polymer membranes for any reasons. The purpose of our tests is to collect basic data to ultimately establish safety standards for fuel cell stacks. Methanol pool flame exposure tests were conducted on stationary use fuel cell stacks of two 200W to evaluate safety in the event of a fire.

Gas behavior during fast filling of a compressed gaseous hydrogen storage tank (Type 3, 35MPa) was simulated numerically to investigate in detail the resulting unsteady temperature distribution and its correlation with the storage tank conditions. The governing equations for the gas phase are the mass, momentum, and energy equations; these equations were discretized using the finite volume method (FVM) in three-dimensional space. The numerical results were carefully compared with the experiment results and have been validated. Consequently, the temperature distributions in space, the time histories of temperature at the measured points, and the filling time to the target pressure were all in good agreement. Furthermore, the unsteady gas and its thermal behavior were clearly visualized in three-dimensional space.

hydrogen was leaked from the underfloor at a flow rate exceeding 131 NL/min (11.8 g/min), which is the allowable fuel leakage rate at the time of a collision of compressed hydrogen vehicles in Japan, and the resulting distribution of concentration in the engine compartment and the dispersion after stoppage of the leak were investigated. Furthermore, ignition tests were also conducted and the impact on the surroundings (mainly on human bodies) was investigated to verify the safety of the allowable leakage rate. The tests clarified that if hydrogen leaks from the underfloor at a flow rate of 1000 NL/min (89.9 g/min) and is ignited in the engine compartment, people around the vehicle will not be seriously injure. Therefore, it can be said that a flow rate of 131 NL/min (11.8 g/min), the allowable fuel leakage rate at the time of a collision of compressed hydrogen vehicles in Japan, assures a sufficient level of safety.

The distribution of concentrations of hydrogen leaking into the front compartment and the dispersion after the leak was stopped were investigated to obtain basic data for specifying the mounting positions of hydrogen leak detecting sensors and the threshold values of alarms for compressed hydrogen vehicles. Ignition tests were also conducted to investigate the flammability and the environmental impact (i.e. the impact on human bodies). These tests were also conducted with methane to evaluate the protection against hydrogen leaks in vehicles in comparison with natural gas (methane). We found that the concentration of hydrogen in the front compartment reached 23.7 vol% maximum when hydrogen gas was allowed to leak for 600 sec from the center of the bottom of the wheelbase at a rate of 131 NL/min, which is the allowable limit for a fuel leak at the time of collision of compressed hydrogen vehicles in Japan.

In this study, we evaluated the fire safety of vehicles that use compressed hydrogen as fuel. We conducted fire tests on vehicles that used compressed hydrogen and on vehicles that used compressed natural gas and gasoline and compared temperatures around the vehicle and cylinder, internal pressure of the cylinder, irradiant heat around the vehicle, sound pressure levels when the pressure relief device (PRD) was activated, and damage to the vehicle and surrounding flammable objects. The results revealed that vehicles equipped with compressed hydrogen gas cylinders are not more dangerous than CNC or gasoline vehicles, even in the event of a vehicle fire.

To determine the appropriateness of specifying the allowable amount of hydrogen leakage upon collision based on the amount of leakage with generated heat equivalent to that of gasoline vehicles and CNG vehicles, we investigated the safety of each type of fuel when flame ignites. Our results confirm that the flame lengths for hydrogen and methane are almost equal, and there is no remarkable difference between them in terms of the distance for assuring safety. Furthermore, we confirmed that the irradiant heat flux from the mixed burning of hydrogen flame with liquid flammable materials is almost equal to that of the spray flame of gasoline. Thus, no clear difference was found between various types of fuel. Therefore, it is appropriate to specify the allowable amount of hydrogen leakage based on the amount of leakage with generated heat equivalent to that of other types of fuel.

To investigate methods of conducting flame exposure tests (bonfire tests) on high-pressure hydrogen gas cylinders that are safe and have high accuracy across repeated tests, we used numerical simulation and experiments to analyze the feasibility of using substitutive gases for filling as well as the effects of the burners used as the fire source. Through a series of virtual experiments using substitutive gases, flame scales, and filling pressure as parameters, we examined the maximum internal pressure, the rate of pressure rise, and the starting time of Pressure Relief Device (PRD) activation. Because substitutive gas properties differ from those of hydrogen gas, we concluded that using substitutive gases would be inappropriate. In addition, we observed that when the flame scale was small, the cylinder's internal pressure before the thermal-activated PRD activation, the rate of pressure rise, and the starting time of PRD activation all increased rapidly.

The high-pressure hydrogen gas cylinder of a fuel-cell vehicle is equipped with a pressure relief device (PRD) to prevent the rupture of the cylinder due to heating by fire. Flame exposure tests (bonfire tests) are conducted to evaluate the safety of the cylinder with the PRD, specifically, cylinder resistance to fire and performance of the PRD. In this study, however, fire tests of vehicles equipped with high-pressure cylinders were not required for this test method. We implemented released-hydrogen flame tests by performing bonfire tests and fire tests on vehicles equipped with hydrogen-filled high-pressure gas cylinders (20,35MPa) to examine safety measures for fuel-cell vehicles. We then investigated the following: the characteristics of the released-hydrogen flame, radiation heat flux from the jet flame, combustion noise, the rate of pressure rise in the cylinder, the venting direction of the PRD, and behavior of fire in conjunction with a gasoline flame.