A wide variety of hydrogen storage technologies are overviewed and typical safety aspects are briefly discussed. Compressed gas will be first utilized beyond the scheduled dawn of fuel cell vehicle economy in 2015. Liquefied hydrogen will also acquire people’s recognition to some extent, but solidification of hydrogen will suffer from trade off problems between volumetric hydrogen capacity and safety.

Japan Petroleum Energy Center have studied safety issues related to hydrogen fuelling station under NEDO initiative. This article describes the outline of the project and several area of the study.

Liquid hydrogen (LH2) has been produced for space technologies since 1950s, and currently its demand is increasing for chemical materials. From the beginning, we have been aware of the hazardous potential of LH2, and its handling was accomplished by safety measures in compliance with codes and standards. With regards to accidents scenario where LH2 involves us, various experiments have been demonstrated to reduce the hazardous potential. And also accident statistics on LH2 have been investigated. Their results showed that LH2 was safety compared to compressed hydrogen gas (GH2). This paper describes the comparison of LH2 and GH2 on safety, activities of transporting LH2 in USA, the statistics of hydrogen accidents, various demonstrating tests and safety handling on LH2.

Safety of hydrogen storage and transportation system by Organic Chemical Hydride (OCH) method is considered. OCH method is expressed in another way that hydrogen is fixed to gasoline component chemically and storage and transportation as same as gasoline under ambient pressure and temperature in the liquid state, because toluene and methylcyclohexane (MCH) are component of gasoline. Hydrogenation process and transportation of toluene and MCH have been well commercialized in a large scale. Dehydrogenation process can be commercialized as same as hydrogenation process in a large scale plant in the industrial area. Hydrogen station for Fuel Cell Vehicle (FCV) by OCH method is considered that it is also able to be commercialized with miner regulation change in Japan.

Complex hydrides containing NaAIH₄, LiNH₂, Mg(NH₂)₂, LiH and/or LiBH₄ fabricated through mechanochemical process are promising materials for a hydrogen storage material because of their high hydrogen storage capacities, albeit slower kinetics and higher reaction temperature than most of hydrogen storage alloys. If we are to apply these materials in public, common users (not experts) must be well informed how to handle them safely and properly, in order to conform to the international agreement, Globally Harmonized System of Classification and Labelling of Chemicals (GHS), which requires the suppliers of the material to submit the hazard information such as the Materials Safety Data Sheet (MSDS) to the customs and carriers. We thus examined the flammability, pyrophoricity , water reactivity and dust-explosibility of the complex hydrides based on the testing procedures provided in the Fire Service Act (a Japanese domestic law), the United Nations’ Recommendation on the Transport of Dangerous Goods and so on. In addition, the eruption tests, in which the sample powder was pushed out of a container into the atmosphere with high-pressure H₂, were also examined. It was shown that these complex hydrides should be stored , transported, handled and disposed more carefully than the conventional hydrogen storage alloy.

Hydrogen attracts attention as clean energy of the next generation. In order to put a hydrogen energy system to practical use, the technical development of safe and efficient storage/transportation media is on of the most important subjects. On board hydrogen tank which is under development can be classified into following two types; 1) high pressure hydrogen tank, 2) metal hydride storage tank. However, metal hydride storage tank do not meet the requirement for on board storage of hydrogen in weight densities. Many fuel cell vehicles adopt a high pressure hydrogen tank (35MPa, 70MPa), but have a problem to volumetric density now. This research is the development of a “hybrid hydrogen tank” which is a combination of type 3 high pressure hydrogen tank and metal hydride. “Hybrid hydrogen tank” is superior to a high pressure container of 70MPa in volumetric density. In this paper, the safety of hybrid hydrogen tank will be introduced.

This paper addresses the material selection and safety validation of hydrogen steel tanks for stationary applications. In order to take advantage of its enhanced hardenability, which would allow thicker walls, Ni-Cr-Mo steel (JIS SNCM439 steel) was selected as the candidate steel However, significant losses of ductility and notched tensile strength are observed in gaseous hydrogen when the tensile strength of the steel in air exceeds around 1000MPa. Therefore, the strength level should be limited to less than 1000MPa, which would limit the susceptibility to hydrogen gas embrittlement. For safety validation, several kinds of fracture-mechanics tests were performed on the SNCM439 (reduced strength) steel, which has a tensile strength in air of 942MPa. No cracks were found after the fatigue test which was performed under twice the usual design cyclic stress for hydrogen, while the fatigue crack life in gaseous hydrogen was decreased due to the enhanced crack propagation rate. Based on the crack propagation analysis, it is necessary to perform crack inspections at regular intervals. Moreover, special attention should be paid to the final machining of the internal surface, because surface defects in the machined layer could be the origin of embrittling defects.

There is no denying that safety is the top priority in the society. Hydrogen safety has been reviewed reflecting the 40-year experience in the research and development of hydrogen fuelled internal combustion engine vehicles.

In this paper, first of all, the characteristics of hydrogen were clarified by comparing those of methane and gasoline from safety points of view. Next, safety considerations were reviewed when hydrogen at high pressure and liquid hydrogen were used. Lastly, an example for safety considerations was introduced when a new test bench for hydrogen fuelled engines was set up.