This work describes a large eddy simulation (LES) approach to model high pressure jet fires. Numerical simulations are compared against a large scale vertical, hydrogen jet fire test [Schefer, R. W., Houf, W. G., Williams, T. C., Bourne, B., & Colton, J. (2007). Characterization of high-pressure, under-expanded hydrogen-jet flames. International Journal of Hydrogen Energy, 32(12), 2081-2093], which gives experimental data for blowdown from a tank at an initial pressure of 413 bar through a 5.08 mm diameter nozzle. In this work, conditions 5 s after the start of the release have been taken to simulate a "quasi-steady" state. The work was driven by the need to develop contemporary tools for safety assessment of real scale under-expanded hydrogen jet fires and an aim was to study an LES model performance to reproduce such large scale jet fires in an industrial safety context. Detailed simulations of the flow structure in under-expanded part of the jet are avoided in this work using the notional nozzle concept. The LES combustion model is based on the mixture fraction approach and probability density function to account for flame-turbulence interaction. A flamelet library of the relationship between the instantaneous composition of the reacting mixture and the mixture fraction is calculated in advance. A comparison of experimental observations and simulation results (flame length, flame width) is discussed in view of the grid resolution required for LES and boundary conditions such as turbulence intensity and turbulent length scale at the notional nozzle. (C) 2009 Elsevier Ltd. All rights reserved.

There are a number of hazards associated with small stationary hydrogen and fuel cell applications. In order to reduce the hazards of such installations, and provide guidance to installers, consequence analysis of a number of potential accident scenarios has been carried out within the scope of the EC FP6 project HYPER. This paper summarises the modelling and experimental programme in the project and a number of key results are presented. The relevance of these findings to installation permitting guidelines (IPG) for small stationary hydrogen and fuel cell systems is discussed. A key aim of the activities was to generate new scientific data and knowledge in the field of hydrogen safety, and, where possible, use this data as a basis to support the recommendations in the IPG. The structure of the paper mirrors that of the work programme within HYPER in that the work is described in terms of a number of relevant scenarios as follows: 1. high pressure releases, 2. small foreseeable releases, 3. catastrophic releases, and 4. the effects of walls and barriers. Within each scenario the key objectives, activities and results are discussed. The work on high pressure releases sought to provide information for informing safety distances for high-pressure components and associated fuel storage, activities on both ignited and unignited jets are reported. A study on small foreseeable releases, which could potentially be controlled through forced or natural ventilation, is described. The aim of the study was to determine the ventilation requirements in enclosures containing fuel cells, such that in the event of a foreseeable leak, the concentration of hydrogen in air for zone 2 ATEX is not exceeded. The hazard potential of a possibly catastrophic hydrogen leakage inside a fuel cell cabinet was investigated using a generic fuel cell enclosure model. The rupture of the hydrogen feed line inside the enclosure was considered and both dispersion and combustion of the resulting hydrogen air mixture were examined for a range of leak rates, and blockage ratios. Key findings of this study are presented. Finally the scenario on walls and barriers is discussed; a mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. Conclusions of experimental and modelling work which aim to provide guidance on configuration and placement of these walls to minimise overall hazards is presented.

This paper summarises the results of the research programme in the HYPER project (Installation Permitting Guidance for Hydrogen and Fuel Cells Stationary Applications) [1]. The relevance of scientific findings to installation permitting guidelines (IPG) for small stationary hydrogen and fuel cell systems is discussed. A key aim of the activities was to generate new knowledge in the field of hydrogen safety, and, where possible, use this data as a basis to support the recommendations in the IPG. The structure of the paper mirrors the HYPER research programme in that the work is described in terms of the following relevant scenarios: 1) high pressure releases, 2) small foreseeable releases, 3) catastrophic releases, and 4) the effects of walls and barriers. Within each scenario the key objectives, activities and results are presented. The work on high pressure releases sought to provide information for informing safety distances for high pressure components and associated fuel storage, activities on both ignited and unignited jets are reported. A study on small foreseeable releases, which could potentially be controlled through natural or forced ventilation, is described. The aim of the study was to determine the ventilation requirements in enclosures containing fuel cells, such that in the event of a foreseeable leak, the concentration of hydrogen in air for zone 2 ATEX [2] is not exceeded. The hazard potential of a possibly catastrophic hydrogen leakage inside a fuel cell cabinet was investigated using a generic fuel cell enclosure model. The rupture of the hydrogen feed line inside the enclosure was considered and both dispersion and combustion of the resulting hydrogen-air mixture were examined for a range of leak rates, and blockage ratios. Finally, the

The aim of this study is to gain an insight into the physical phenomena underlying the spontaneous ignition of hydrogen following a sudden release from high-pressure storage and transition to sustained jet fire. The modelling and large-eddy simulation (LES) of the spontaneous ignition dynamics in a tube with a non-inertial rupture disk separating the high-pressure hydrogen storage and the atmosphere is described. Numerical experiments confirmed that due to the stagnation conditions a chemical reaction first commences in the tube boundary layer, and subsequently propagates throughout the tube cross-section. The dynamics of flame formation outside the tube, simulated by the LES model, has reproduced the combustion patterns, including vortex induced "flame separation", which have been experimentally observed by high-speed photography. It is concluded that the LES model can be applied for hydrogen safety engineering, e.g. for the development of innovative pressure relief devices. (c) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

An experimental investigation is conducted into the nature of catalytic ignition of leaked hydrogen gas within an enclosure, and the nature of hydrogen dispersion under varied venting conditions. Using a 1/16th linear scale two-car garage as a model, and a platinum foil as a catalytic surface, it is found that for all conditions tested, catalytic ignition is observed after the leaked hydrogen comes in contact with the catalytic surface, which is initially at or near room temperature. After ignition, these surface reactions lead to steady-state surface temperatures in the range of 600-800 K, dependent on inlet conditions in terms of mixture composition and flow rate. In addition, varying the venting opportunities from the garage walls suggests that not only total area, but also the number and position of vents may impact the nature of hydrogen accumulation within an enclosed structure. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

An experimental investigation into the ignition characteristics of lean pre-mixed hydrogen/air mixtures is conducted using a stagnation-point flow configuration against a platinum surface, with a special emphasis on the determination of potential fire safety hazards associated with hydrogen release in the presence of a catalyst. Two distinct regimes are observed for this system - catalytic surface reactions and gas-phase ignition. It is demonstrated that depending on mixture equivalence ratio, catalytic surface reactions can be initiated with or without surface heating. When significant surface heat is released via catalytic reactions, gas-phase ignition can be induced, greatly increasing the apparent danger of hydrogen leaks in the presence of a platinum surface. The critical surface temperatures leading to catalytic ignition for hydrogen/air mixtures over a platinum surface are further investigated over a range of equivalence ratios and stretch rates. It is shown that ultra-lean hydrogen/air mixtures can be catalytically ignited even in the absence of external heat addition, suggesting that hydrogen leakage in the presence of a platinum surface may pose a fire safety risk even at room temperature. Furthermore, even without a transition to gas-phase ignition, the surface temperature that can be sustained with surface reactions alone may contribute to component degradation or itself pose a safety hazard. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

As a result of the high probability of hydrogen isotope permeation through materials used in high-temperature reactor operations, the interaction Of hydrogen isotopes with metallic structural materials proposed to be used for fusion reactor designing is of great importance for safety considerations. Determining the parameters of the interaction between hydrogen isotopes and different materials, is therefore essential to accurately calculate recycling, outgassing, loading, permeation and hydrogen embrittlement. The permeation tests were made in collaboration with IFIN Bucuresti inside of a special glove-box to avail their radioactive protection expertise. This investigation programme is ongoing. In this paper we describe the permeation stand facility and the preliminary tests carried out to date.

A high temperature reactor (HTR) is a candidate to drive high temperature water-splitting using process heat. While both high temperature nuclear reactors and hydrogen generation plants have high individual degrees of development, study of the coupled plant is lacking. Particularly absent are considerations of the transient behavior of the coupled plant, as well as studies of the safety of the overall plant. The aim of this document is to contribute knowledge to the effort of nuclear hydrogen generation. In particular, this study regards identification of safety issues in the coupled plant and the transient modeling of some leading candidates for implementation in the Nuclear Hydrogen Initiative (NHI). The Sulfur Iodine (SI) and Hybrid Sulfur (HyS) cycles are considered as candidate hydrogen generation schemes. Three thermodynamically derived chemical reaction chamber models are coupled to a well-known reference design of a high temperature nuclear reactor. These chemical reaction chamber models have several dimensions of validation, including detailed steady state flowsheets, integrated loop test data, and bench scale chemical kinetics. The models and coupling scheme are presented here, as well as a transient test case initiated within the chemical plant. The 50%2feed flow failure within the chemical plant results in a slow loss-of-heat sink (LOHS) accident in the nuclear reactor. Due to the temperature feedback within the reactor core the nuclear reactor partially shuts down over 1500 s. Two distinct regions are identified within the coupled plant response: (1) immediate LOHS due to the loss of the sulfuric acid decomposition section and (2) continuing slow LOHS due to the chemical species cascade throughout the plant. (C) 2012 Elsevier B.V. All rights reserved.

Process risk analysis is used in industrial activities to diminish accident potential by the application of prevention or protection techniques to improve process safety. For this purpose, Preliminary Hazard Analysis and HAZOP have been applied to a hydrogen gaseous effluent treatment and purification plant. This plant recovers contaminated gaseous effluent hydrogen from a metallurgical iron powder reduction furnace. Purified hydrogen is recycled to the process. The process safety studies included hazard identification and consequences to material, equipment and people. The study proposed specific process safety measures and future additional process safety studies.

In this work, we present recent progress in our work to develop new sensors and sensing technology for future hydrogen powered fuel cell vehicles. The first device is an electrochemical mixed potential sensor based on an indium-tin oxide/YSZ/Pt configuration prototype fabricated using commercial ceramic sensor manufacturing methods. This sensor has been designed to detect hydrogen in air and may serve in safety systems for vehicles or as a component of hydrogen infrastructure. The second device relies on a swept frequency acoustic method to non-invasively determine the state of charge of a hydride material contained within a sealed storage system.