Safety
Self-ignition and Flame Propagation of Pressurized Hydrogen Released Through Tubes
Sep 2019
Publication
The spontaneous ignition of hydrogen released from the high pressure tank into the downstream pipes with different lengths varied from 0.3m to 2.2m has been investigated experimentally. In this study the development of shock wave was recorded by pressure sensors and photoelectric sensors were used to confirm the presence of a flame in the pipe. In addition the development of jet flame was recorded by high-speed camera and IR camera. The results show that the minimal release pressure in different tube when self-ignition of hydrogen occurred could decrease first and then increase with the increase of the aspect of pipe. And the minimum release pressure of hydrogen self-ignition was 3.87MPa. When the flame of self-ignition hydrogen spouted out of the tube Mach disk was observed. The method of CFD was adopted. The development of shock wave at the tube exit was reproduced and structures as barrel shock the reflected shock and the Mach disk are presented. Because of these special structures the flame at the nozzle is briefly extinguished and re-ignited. At the same time the complete development process of the jet flame was recorded including the formation and separation of the spherical flame. The flame structure exhibits three typical levels before the hemispherical flame separation.
Hydrogen for Renewable Energy Export: Broadening the Concept of Hydrogen Safety
Sep 2019
Publication
Recently we have seen hydrogen (re)emerge as an important component of widespread decarbonisation of energy sectors. From an Australian perspective this brings with it an opportunity to store transport and export renewable energy—either as liquefied hydrogen or in a carrier such as ammonia. The growth of the hydrogen industry to now include the power and transport sectors as well as the notion of hydrogen export has broadened the range of safety considerations required and seen them extend into the realm of the consumer for the first time.<br/>Hydrogen as well as ammonia and other carriers such as methanol are existing industrial chemicals which have established protocols for their handling and use in the chemicals sector. As their use in energy and transport increases especially in the context of widespread domestic use their handling and use by inexperienced people in less-controlled environments expands shifting the risk profiles and management systems required. There is also the potential for novel hydrogen carriers such as methylcyclohexane/toluene to reach commercial viability at industrial scale.<br/>This paper will discuss some of these emerging applications of hydrogen and its carriers and discuss some of the technological innovations under development that may accompany a new energy industry— with some consideration given to their potential risks and the required safety considerations. In addition we will also provide an overview of global activity in this area and how new standards and regulations would need to be developed for the adaption of these technologies in an Australian context.
Numerical Investigation of Hydrogen-air Deflagrations in a Repeated Pipe Congestion
Sep 2019
Publication
Emerging hydrogen energy technologies are creating new avenues for bring hydrogen fuel usage into larger public domain. Identification of possible accidental scenarios and measures to mitigate associated hazards should be well understood for establishing best practice guidelines. Accidentally released hydrogen forms flammable mixtures in a very short time. Ignition of such a mixture in congestion and confinements can lead to greater magnitudes of overpressure catastrophic for both structure and people around. Hence understanding of the permissible level of confinements and congestion around the hydrogen fuel handling and storage unit is essential for process safety. In the present study numerical simulations have been performed for the hydrogen-air turbulent deflagration in a well-defined congestion of repeated pipe rig experimentally studied by [1]. Large Eddy Simulations (LES) have been performed using the in-house modified version of the OpenFOAM code. The Flame Surface Wrinkling Model in the LES context is used for modelling deflagrations. Numerical predictions concerning the effects of hydrogen concentration and congestion on turbulent deflagration overpressure are compared with the measurements [1] to provide validation of the code. Further insight about the flame propagation and trends of the generated overpressures over the range of concentrations are discussed.
Large Scale Experiments and Model Validation of Pressure Peaking Phenomena-ignited Hydrogen Releases
Jan 2021
Publication
The Pressure Peaking Phenomena (PPP) is the effect of introducing a light gas into a vented volume of denser gas. This will result in a nonequilibrium pressure as the light gas pushes the dense gas out at the vent. Large scale experiments have been performed to produce relevant evidence. The results were used to validate an analytical model. Pressure and temperature were measured inside a constant volume while the mass flow and vent area were varied. The analytical model was based on the conservation of mass and energy. The results showed that increasing the mass flow rate the peak pressure increases and with increasing the ventilation area the peak pressure decreases. Peak pressure was measured above 45 kPa. Longer combustion time resulted in higher temperatures increasing an underpressure effect. The experimental results showed agreement with the analytical model results. The model predicts the pressures within reasonable limits of+/-2 kPa. The pressure peaking phenomena could be very relevant for hydrogen applications in enclosures with limited ventilation. This could include car garages ship hull compartments as well as compressor shielding. This work shows that the effect can be modeled and results can be used in design to reduce the consequences.
Prediction of Pressure Reduction Rate in 30 m3 Liquid Hydrogen Tank Based on Experimental and Numerical Analysis
Sep 2019
Publication
Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large scale transport and storage of hydrogen with higher densities and potentially better safety performance. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducts pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The work program consists of a preparatory phase where the state of the art before the project has been summarized and where the experimental planning was adjusted to the outcome of a research priorities workshop. The central part of the project consists of 3 phenomena oriented work packages addressing Release Ignition and Combustion with analytical approaches experiments and simulations. The results shall improve the general understanding of the behaviour of LH2 in accidents and thereby enhance the state-of-the-art what will be reflected in appropriate recommendations for development or revision of specific international standards. The paper presents the status of the project at the middle of its terms.
Cautiously Optimistic: Understanding the Australian Public’s Response to the Hydrogen Opportunity
Sep 2019
Publication
The increased activity across the technical world for developing hydrogen has not gone unnoticed at the political level. However there remains a gap in understanding of how the general public will respond to the development of such an emergent industry. Recognising this gap we undertook ten focus groups (N=92) and a nationally representative online survey (N=2785) with the Australian public to better understand their response to hydrogen and the opportunities it presents for export and domestic use. In both focus groups and the national survey when Australians first heard the word hydrogen they were most likely to respond with a neutral response. For example in the survey 81% responded with words such as gas energy water; with only 13% giving negative associations (e.g. bomb explosion Hindenburg); and 3% positive (e.g. clean future). Males were more likely to be supportive of hydrogen than females. Those who answered more knowledge questions correctly were also more supportive. The main benefits associated with the use of hydrogen technologies centred around the environment - reduced greenhouse gas emissions and climate change mitigation potential were key benefits. With safety cost and environmental impacts - particularly concerns around pollution emissions and water use - being the most frequently cited concerns about the production and use of hydrogen. This presentation focuses on Australian attitudes to the developing hydrogen export opportunity and also for domestic use. Implications for industry and policy makers will be discussed in light of these Australians responses.
Implementation of Large Scale Shadowgraphy in Hydrogen Safety Phenomena
Sep 2013
Publication
We have implemented a portable large-scale shadowgraph system for use in flow visualization relating to hydrogen safety. Previous large-scale shadowgraph and schlieren implementations have often been limited to background- oriented techniques which are subject to noise. The system built is based on a large-scale shadowgraph technique developed by Settles which allows for high-quality visualization. We have applied the shadowgraph system to complex phenomena and current issues in hydrogen safety including DDT in long channels jet releases and unconfined deflagrations. Shadowgrams taken are compared to a Z-schlieren system. This shadowgraph system allows analysis of these phenomena at longer length scales.
Self-acceleration of a Spherically Expanding Hydrogen-air Flame at Elevated Pressure
Sep 2019
Publication
Self-acceleration of a spherically expanding hydrogen-air flame was experimentally investigated in a closed dual-chamber apparatus with the quartz windows enabled to a flame diameter with up to 240 mm. The flame radius and flame speed in lean hydrogen-air mixtures at elevated pressure were evaluated using a high speed Schlieren photography. The experimental results from hydrogen-air explosion at elevated pressure validated the prediction model for self-similar propagation. The flame radius and its speed calculated by the prediction models agree well with the experimental results of hydrogen-air explosions at elevated pressure. Furthermore the acceleration exponent α is evaluated by plotting the flame radius with time. The results show the α value increase with the dimensionless flame radius r/rcl. It is indicated that the self-acceleration and the transition regime to self-similar propagation exist in the spherically expanding hydrogen-air flame.
Assessing the Viability of the ACT Natural Gas Distribution Network for Reuse as a Hydrogen Distribution Network
Sep 2019
Publication
The Australian Capital Territory (ACT) has legislated and aims to be net zero emissions by 2045. Such ambitious targets have implications for the contribution of hydrogen and its storage in gas distribution networks Therefore we need to understand now the impacts on the gas distribution network of the transition to 100% hydrogen. Assessment of the viability of decarbonising the ACT gas network will be partly based on the cost of reusing the gas network for the safe and reliable distribution of hydrogen. That task requires each element of the natural gas safety management system to be evaluated.
This article describes the construction of a test facility in Canberra Australia used to identify issues raised by 100% hydrogen use in the medium pressure distribution network consisting of nylon and polyethylene (PE) as a means of identifying measures necessary to ensure ongoing validity of the network's regulatory safety case.
Evoenergy (the ACT's gas distribution company) have constructed a Test Facility incorporating an electrolyser a gas supply pressure reduction and mixing skid a replica gas network and a domestic installation with gas appliances. Jointly with Australian National University (ANU) and Canberra Institute of Technology (CIT) the Company has commenced a program of “bench testing” initially with 100% hydrogen to identify gaps in the safety case specifically focusing on the materials work practices and safety systems in the ACT.
The facility is designed to assess:
The paper addresses major safety issues relating to the production/storage distribution and consumer end use of hydrogen injected into existing gas distribution networks. The analysis is guided by the Safety Management System. The Hydrogen Testing Facility described in the paper provide tools for evaluation of hydrogen safety matters in the ACT and Australia-wide.
Testing to date has confirmed that polyethylene and nylon pipe and their respective jointing techniques can contain 100% hydrogen at pressures used for the distribution of natural gas. Testing has also confirmed that current installation work practices on polyethylene and nylon pipe and joints are suitable for hydrogen service. This finding is subject to variation attributable to staff training and skill levels and further testing has been programmed as outlined in this paper.
Testing of gas isolation by clamping and simulated repair on the hydrogen network has established that standard natural gas isolation techniques work with 100% hydrogen at natural gas pressures.
This article describes the construction of a test facility in Canberra Australia used to identify issues raised by 100% hydrogen use in the medium pressure distribution network consisting of nylon and polyethylene (PE) as a means of identifying measures necessary to ensure ongoing validity of the network's regulatory safety case.
Evoenergy (the ACT's gas distribution company) have constructed a Test Facility incorporating an electrolyser a gas supply pressure reduction and mixing skid a replica gas network and a domestic installation with gas appliances. Jointly with Australian National University (ANU) and Canberra Institute of Technology (CIT) the Company has commenced a program of “bench testing” initially with 100% hydrogen to identify gaps in the safety case specifically focusing on the materials work practices and safety systems in the ACT.
The facility is designed to assess:
- Materials in use including aged network materials and components
- Construction and installation techniques both greenfield and live gas work
- Purging and filling techniques
- Leak detection both underground and above ground
- Emergency response and make safe techniques
- Issues associated with use of hydrogen in light commercial and domestic appliances.
- Technicians and gas fitters on infrastructure installation and management
- Emergency response services on responding to hydrogen related emergencies in a network environment; and
- Manage public perceptions of hydrogen in a network environment.
The paper addresses major safety issues relating to the production/storage distribution and consumer end use of hydrogen injected into existing gas distribution networks. The analysis is guided by the Safety Management System. The Hydrogen Testing Facility described in the paper provide tools for evaluation of hydrogen safety matters in the ACT and Australia-wide.
Testing to date has confirmed that polyethylene and nylon pipe and their respective jointing techniques can contain 100% hydrogen at pressures used for the distribution of natural gas. Testing has also confirmed that current installation work practices on polyethylene and nylon pipe and joints are suitable for hydrogen service. This finding is subject to variation attributable to staff training and skill levels and further testing has been programmed as outlined in this paper.
Testing of gas isolation by clamping and simulated repair on the hydrogen network has established that standard natural gas isolation techniques work with 100% hydrogen at natural gas pressures.
Inhibition of Confined Hydrogen Explosion by Inert Gases
Sep 2019
Publication
"This paper is aimed at revealing the inhibiting effects of He Ar N2 and CO2 on confined hydrogen explosion. The flame characteristics under thermo diffusive instability and hydrodynamic instability are analyzed using Lewis number and ratio of density ratio to flame thickness. The inhibiting effects of inert gas on confined hydrogen explosion are evaluated using maximum explosion pressure and maximum pressure rise rate. The inhibiting mechanism is obtained by revealing thermal diffusivity maximum mole fraction and net reaction rate of active radicals. The results demonstrated that the strongest destabilization effect of hydrodynamic instability and thermodiffusive instability occurs when the inert gas is Ar and CO2 respectively. Taking maximum explosion pressure and maximum rate of pressure rise as an indicator the effects of confined hydrogen explosion inhibition from strong to weak are CO2 N2 Ar and He. Laminar burning velocity thermal diffusivity maximum mole fraction and net reaction rate of active radicals continues to decrease in the order of He Ar N2 and CO2. The elementary reactions of generating and consuming active radicals at the highest net reaction rate are mainly consisted of R1 (H+O2=OH+O) R2 (H2+O=OH+H) R3 (H2+OH=H2O+H) and R10 (HO2+H=2OH).
Evaluation of an Improved Vented Deflagration CFD Model Against Nine Experimental Cases
Sep 2019
Publication
In the present work a newly developed CFD deflagration model incorporated into the ADREA-HF code is evaluated against hydrogen vented deflagrations experiments carried out by KIT and FM-Global in a medium (1 m3) and a real (63.7 m3) scale enclosure respectively. A square vent of 0.5 m2 and 5.4 m2 respectively is located in the center of one of side walls. In the case of the medium scale enclosure the 18% v/v homogeneous hydrogen-air mixture and back-wall ignition case is examined. In the case of the real scale enclosure the examined cases cover different homogeneous mixture concentrations (15% and 18% v/v) different ignition locations (back-wall and center) and different levels of initial turbulence. The CFD model accounts for flame instabilities that develop as the flame propagates inside the chamber and turbulence that mainly develops outside the vent. Pressure predictions are compared against experimental measurements revealing a very good performance of the CFD model for the back-wall ignition cases. For the center ignition cases the model overestimates the maximum overpressure. The opening of the vent cover is identified as a possible reason for the overprediction. The analysis indicates that turbulence is the main factor which enhances external explosion strength causing the sudden pressure increase confirming previous findings.
Delivering a Safe, Viable Hydrogen Economy in Australia
Sep 2019
Publication
At Woodside Energy Ltd (Woodside) safety is built into everything we do and progressing hydrogen opportunities is no exception. This paper will present information from the macro level of process safety for hydrogen at a plant level through to the consumer experience. Examples of the benefits of an integrated process safety approach will be used from Woodside’s experience pioneering the liquefied natural gas industry in Australia.<br/>This paper will underscore the reasons why Australia needs to adopt robust safety standards for hydrogen as quickly as possible in order to advance the hydrogen economy across all sectors. Focus areas requiring attention during development of standards and potential mechanisms to close will be proposed. Establishing a hydrogen economy in Australia could lower carbon emissions stabilise power grids increase renewable energy penetration and create jobs. Developing Australian standards that are fully aligned with international standards will facilitate Australia taking a leading role in the global hydrogen economy.
Vented Hydrogen Deflagrations in Containers: Effect of Congestion for Homogeneous Mixtures
Sep 2017
Publication
This paper presents results from an experimental study of vented hydrogen deflagrations in 20-foot ISO containers. The scenarios investigated include 14 tests with explosion venting through the doors of the containers and 20 tests with venting through openings in the roof. The parameters investigated include hydrogen concentration vent area type of venting device and the level of congestion inside the containers. All tests involved homogeneous and initially quiescent hydrogen-air mixtures. The results demonstrate the strong effect of congestion on the maximum reduced explosion pressures which typically is not accounted for in current standards and guidelines for explosion protection. The work is a deliverable from work package 2 (WP2) in the project “Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations” or HySEA which receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461.
Indoor Use of Hydrogen, Knowledge Gaps and Priorities for the Improvement of Current Standards on Hydrogen, a Presentation of HyIndoor European Project
Sep 2013
Publication
To develop safety strategies for the use of hydrogen indoors the HyIndoor project is studying the behaviour of a hydrogen release deflagration or non-premixed flame in an enclosed space such as a fuel cell or its cabinet a room or a warehouse. The paper proposes a safety approach based on safety objectives that can be used to take various scenarios of hydrogen leaks into account for the safe design of Hydrogen and Fuel Cell (HFC) early market applications. Knowledge gaps on current engineering models and unknown influence of specific parameters were identified and prioritized thereby re-focusing the objectives of the project test campaign and numerical simulations. This approach will enable the improvement of the specification of openings and use of hydrogen sensors for enclosed spaces. The results will be disseminated to all stakeholders including hydrogen industry and RCS bodies.
Risk Identification for the Introduction of Advanced Science and Technology: A Case Study of a Hydrogen Energy System for Smooth Social Implementation
May 2020
Publication
A method of risk identification is developed by comparing existing and advanced technologies from the viewpoint of comprehensive social risk. First to analyze these values from a multifaceted perspective we constructed a questionnaire based on 24 individual values and 26 infrastructural values determined in a previous study. Seven engineering experts and six social science experts were then asked to complete the questionnaire to compare and analyze a hydrogen energy system (HES) and a gasoline energy system (GES). Finally the responses were weighted using the analytic hierarchy process. Three important points were identified and focused upon: the distinct disadvantages of the HES compared to the GES judgments that were divided between experts in the engineering and social sciences fields and judgments that were divided among experts in the same field. These are important risks that should be evaluated when making decisions related to the implementation of advanced science and technology.
Safe Hydrogen Fuel Handling and Use for Efficient Implementation – SH2IFT
Sep 2019
Publication
The SH2IFT project combines social and technical scientific methods to address knowledge gaps regarding safe handling and use of gaseous and liquid hydrogen. Theoretical approaches will be complemented by fire and explosion experiments with emphasis on topics of strategic importance to Norway such as tunnel safety maritime applications etc. Experiments include Rapid Phase Transition Boiling Liquid Expanding Vapour Explosion and jet fires. This paper gives an overview of the project and preliminary results.
Numerical Study of the Detonation Benchmark using GASFLOW-MPI
Sep 2019
Publication
Hydrogen has been widely used as an energy carrier in recent years. It should a better understand of the potential hydrogen risk under the unintended release of hydrogen scenario since the hydrogen could be ignited in a wide range of hydrogen concentrations in the air and generate a fast flame speed. During the accidental situation the hydrogen-air detonation may happen in the large-scale space which is viewed as the worst case state of affairs. GASFLOW-MPI is a powerful CFD-based numerical tool to predict the complicated hydrogen turbulent transport and combustion dynamics behaviours in the three-dimensional large-scale industrial facility. There is a serious of well-developed physical models in GASFLOW-MPI to simulate a wide spectrum of combustion behaviours ranging from slow flames to deflagration-to-detonation transition and even to detonation. The hydrogen–air detonation experiment which was carried out at the RUT tunnel facility is a well-known benchmark to validate the combustion model. In this work a numerical study of the detonation benchmark at RUT tunnel facility is performed using the CFD code GASFLOW-MPI. The complex shock wave structures in the detonation are captured accurately. The experimental pressure records and the simulated pressure dynamics are compared and discussed.
Quantifying the Potential Consequences of a Detonation in a Hydrogen Jet Release
Sep 2019
Publication
The unconfined release of high-pressure hydrogen can create a large flammable jet with the potential to generate significant damage. To properly understand the separation distances necessary to protect the immediate surroundings it is important to accurately assess the potential consequences. In these events the possibility for a detonation cannot be excluded and would generally result in the worst case scenario from the standpoint of damaging overpressure. The strong concentration gradients created by a jet release however raises the question of what portion of the flammable cloud should be considered. Often all of the fuel within the limits of fast-flame acceleration or even all of the fuel within the flammability range is considered which typically comprises the majority of the flammable cloud. In this work prior detonation studies are reviewed to illustrate the inherently unstable nature of detonations with a focus on the critical dimensions and concentration gradients that can support a propagating detonation wave. These criteria are then applied to the flammable cloud concentration distributions generated by an unconfined jet release of hydrogen. By evaluating these limits it is found that the portion of the flammable cloud that is likely to participate is significantly reduced. These results are compared with existing experimental data on the ignition of unconfined hydrogen releases and the peak pressures that were measured are consistent with a detonation of a mass of fuel that is equivalent to the model prediction for the mass of fuel within the detonable limits. This work demonstrates how the critical conditions for detonation propagation can be used to estimate the portion of a hydrogen release that could participates in a detonation and how these criteria can be readily incorporated into existing dispersion modelling approaches.
Hydrogen Safety- From Policies to Plans to Practices
Sep 2005
Publication
Safety is an essential element for realizing the “hydrogen economy” – safe operation in all of its aspects from hydrogen production through storage distribution and use; from research development and demonstration to commercialization. As such safety is given paramount importance in all facets of the research development and demonstration of the U.S Department of Energy’s (DOE) Hydrogen Fuel Cells and Infrastructure Technologies (HFCIT) Program Office. The diversity of the DOE project portfolio is self-evident. Projects are performed by large companies small businesses DOE National Laboratories academic institutions and numerous partnerships involving the same. Projects range from research exploring advances in novel hydrogen storage materials to demonstrations of hydrogen refuelling stations and vehicles. Recognizing the nature of its program and the importance of safety planning DOE has undertaken a number of initiatives to encourage and shape safety awareness. The DOE Hydrogen Safety Review Panel was formed to bring a broad cross-section of expertise from the industrial government and academic sectors to help ensure the success of the program as a whole. The Panel provides guidance on safety-related issues and needs reviews individual DOE-supported projects and their safety plans and explores ways to bring learnings to broadly benefit the DOE program. This paper explores the approaches used for providing safety planning guidance to contractors in the context of their own (and varied) policies procedures and practices. The essential elements that should be included in safety plans are described as well as the process for reviewing project safety plans. Discussion of safety planning during the conduct of safety review site visits is also shared. Safety planning-related learnings gathered from project safety reviews and the Panel’s experience in reviewing safety plans are discussed.
Sensitivity to Detonation and Detonation Cellular Structure of H2-O2-AIr-H2O2 Gas Mixtures
Sep 2005
Publication
Today it is not known – neither qualitatively not quantitatively - how large the impact can be of the promoters on sensitivity to hydrogen-air detonation in hypothetical accidents at hydrogen-containing installations transport or storage facilities. Report goal is to estimate theoretically an effect of hydrogen-peroxide (as representative promoter) on sensitivity to detonation of the stoichiometric hydrogen-oxygen gas mixtures. The classical H2-O2-Ar (2:1:7) gas mixture was chosen as reference system with the well established and unambiguously interpreted experimental data. In kinetic simulations it was found that the ignition delay time is sensitive to H2O2addition for small initial H2O2concentrations and is nearly constant for the large ones. Parametric reactive CFD studies of two dimensional cellular structure of 2H2-O2-7Ar-H2O2 detonations with variable hydrogen peroxide concentration (up to 10 vol.%) were also performed. Two un-expected results were obtained. First result: detonation cell size is practically independent upon variation of initial hydrogen peroxide concentration. For practical applications it means that presence of hydrogen-peroxide did not change drastically sensitivity of the stoichiometric hydrogen-oxygen gas mixtures. These theoretical speculations require an experimental verification. Second result: for large enough initial H2O2concentrations (> 1 vol.% at least) a new element of cellular structure of steady detonation wave was revealed. It is a system of multiple secondary longitudinal shock waves (SLSW) which propagates in the direction opposite to that of the leading shock wave. Detailed mechanism of SLSW formation is proposed.
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