Safety

We conducted a fuelling test with hydrogen gas for a safety evaluation of the nozzle/receptacle at a controlled temperature and humidity. Test results confirmed that the nozzle/receptacle froze under specific conditions. However freezing did not cause apparatus damage nor hydrogen leakage. The nozzle/receptacle is thus able to fuel safely even if the nozzle/receptacle is stuck due to ice. In addition we quantified the water volume that causes freezing.

In 2005 the Japanese High-pressure Gas Safety Act the Fire Service Act and the Building Standards Act were revised to establish the requirements for 35 MPa hydrogen stations. And in 2012-2014 revisions were made to the High-pressure Gas Safety Act and the Fire Service Act to provide the regulatory requirements for 70 MPa hydrogen stations. We conducted a study on materials that may contribute to prepare technical standards concerning the major 4 items 12 additional items and 13 new items which may affect the costs from the point of view of promoting the hydrogen infrastructure.

In the accident of Fukushima Daiichi nuclear power plants hydrogen was accumulated in the reactor buildings and exploded. To prevent such explosions hydrogen venting from reactor buildings is considered. When the gas mixture is released to a reactor building through a reactor containment together with the hydrogen some amount of steam might also be released. The steam condenses if the building atmosphere is below the saturation temperature and it affects the hydrogen behaviour. In this study the condensation effect to the hydrogen venting is evaluated using CFD analyses by comparing the case where a hydrogen-nitrogen mixture is released and the case where a hydrogen-steam mixture is released.

This paper shows the experimental results and findings of field explosion tests conducted to obtain fundamental data concerning the explosion of hydrogen-air mixtures. A tent covered with thin plastic sheets was filled with hydrogen/air mixed gas and subsequently ignited by an electric-spark or explosives to induce deflagration and/or detonation. Several experiments with different concentrations and/or volumes of mixture were carried out. The static overpressure of blast waves was measured using piezoelectric pressure sensors. The recorded data show that the shape of the pressure-time histories of the resulting blast waves depends on the difference in the ignition method used. The pictures of the explosion phenomenon (deflagration and/or detonation) were taken by high-speed cameras.

This paper presents a compilation and discussion of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V1 which is based on an experiment on hydrogen release mixing and distribution inside a vessel. Each partner has his own point of view of the problem and uses a different approach to the solution. The main characteristics of the models employed for the calculations are compared. The comparison between results together with the experimental data when available is made. Relative deviations of each model from the experimental values are also included. Explanations and interpretations of the results are presented together with some useful conclusions for future work.

To make “Hydrogen vehicles and refuelling station systems” fit for public use research on hydrogen safety and designing mitigative measures are significant. For compact storage it is planned to store under high pressure (40MPa) at the refuelling stations so that the safety for the handling of high-pressurized hydrogen is essential. This paper describes the experimental investigation on the hypothetical dispersion and explosion of high-pressurized hydrogen gas which leaks through a large scale break in piping and blows down to atmosphere. At first we investigated time history of distribution of gas concentration in order to comprehend the behaviour of the dispersion of high-pressurized hydrogen gas before explosion experiments. The explosion experiments were carried out with changing the time of ignition after the start of dispersion. Hydrogen gas with the initial pressure of 40MPa was released through a nozzle of 10mm diameter. Through these experiments it was clarified that the explosion power depends not only on the concentration and volume of hydrogen/air pre-mixture but also on the turbulence characteristics before ignition. To clarify the explosion mechanism the numerical computer simulation about the same experimental conditions was performed. The initial conditions such as hydrogen distribution and turbulent characteristics were given by the results of the atmospheric diffusion simulation. By the verification of these experiments the results of CFD were fully improved.

The development and promulgation of codes and standards are essential to establish a market-receptive environment for commercial hydrogen-based products and systems. The focus of the U.S. Department of Energy (DOE) is to conduct the research and development (R&D) needed to strengthen the scientific basis for technical requirements incorporated in national and international standards codes and regulations. In the U.S. the DOE and its industry partners have formed a Codes and Standards Tech Team (CSTT) to help guide the R&D. The CSTT has adopted an R&D Roadmap to achieve a substantial and verified database of the properties and behaviour of hydrogen and the performance characteristics of emerging hydrogen technology applications sufficient to enable the development of effective codes and standards for these applications. However to develop a more structured approach to the R&D described above the CSTT conducted a workshop on Risk Assessment for Hydrogen Codes and Standards in March 2005. The purpose of the workshop was to attain a consensus among invited experts on the protocols and data needed to address the development of risk-informed standards codes and regulations for hydrogen used as an energy carrier by consumers. Participants at the workshop identified and assessed requirements methodologies and applicability of risk assessment (RA) tools to develop a framework to conduct RA activities to address for example hydrogen fuel distribution delivery on-site storage and dispensing and hydrogen vehicle servicing and parking. The CSTT was particularly interested in obtaining the advice of RA experts and representatives of standards and model code developing organizations and industry on how data generated by R&D can be turned into information that is suitable for hydrogen codes and standards development. The paper reports on the results of the workshop and the RA activities that the DOE’s program on hydrogen safety codes and standards will undertake. These RA activities will help structure a comprehensive R&D effort that the DOE and its industry partners are undertaking to obtain the data and conduct the analysis and testing needed to establish a scientific and technical basis for hydrogen standards codes and regulations.

A new testing device for cyclic loading of specimens with a novel shape design is presented. The device was applied for investigations of fatigue of metallic specimens under pressurized hydrogen up to 300 bar at temperatures up to 200 °C. Main advantage of the specimen design is the very small amount of medium here hydrogen used for testing. This allows experiments with hazardous substances at lower safety level. Additionally no gasket for the load transmission is required. Woehler curves which show the influence of hydrogen on the fatigue behaviour of austenitic steel specimens at relevant service conditions in hydrogen powered engines are presented. Material and test conditions are in agreement with the cooperating industry.

In order to facilitate the introduction of a new technology as it is the utilization of hydrogen as an energy carrier development of safety codes and standards besides the conduction of demonstrative projects becomes a very important action to be realized. Useful tools of work could be the existing gaseous fuel codes (natural gas and propane) regulating the stationary and automotive applications. Some safety codes have been updated to include hydrogen but they have been based on criteria and/or data applicable for large industrial facilities making the realization of public hydrogen infrastructures prohibitive in terms of space. In order to solve the above mentioned problems others questions come out: how these safety distances have been defined? Which hazard events have been taken as reference for calculation? Is it possible to reduce the safety distances through an appropriate design of systems and components or through the predisposition of adequate mitigation measures? This paper presents an analysis of the definitions of “safety distances” and “hazardous locations” as well as a synoptic analysis of the different values in force in several States for hydrogen and natural gas. The above mentioned synoptic table will highlight the lacks and so some fields that need to be investigated in order to produce a suitable hydrogen standard.

Flame acceleration and deflagration to detonation transition (DDT) is simulated with a numerical code based on a flux limiter centred method for hyperbolic differential equations. The energy source term is calculated by a Riemann solver for the in homogeneous Euler equations for the turbulent combustion and a two-step reaction model for hydrogen-air. The transport equations are filtered for large eddy simulation (LES) and the sub filter turbulence is modelled by a transport equation for the the turbulent kinetic energy. The flame tracking is handled by the G-equation for turbulent flames. Numerical results are compared to pressure histories from physical experiments. These experiments are performed in a closed circular 4m long tube with inner diameter of 0.107m. The tube is filled with hydrogen-air mixture at 1atm which is at rest when ignited. The ignition is located at one end of the tube. The tube is fitted with an obstruction with circular opening 1m down the tube from the ignition point. The obstruction has a blockage ratio of 0.92 and a thickness of 0.01m. The obstruction creates high pressures in the ignition end of the tube and very high gas velocities in and behind the obstruction opening. The flame experiences a detonation to deflagration transition (DDT) in the super sonic jet created by the obstruction. Pressure build-up in the ignition end of the tube is simulated with some discrepancies. The DDT in the supersonic jet is simulated but the position of the DDT is strongly dependent on the simulated pressure in the ignition end.