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THIS ANNUAL SCIENCE Review showcases the high quality of science evidence and analysis that underpins HSE’s risk-based regulatory regime. To be an effective regulator HSE has to balance its approaches to informing directing advising and enforcing through a variety of activities. For this we need capacity to advance knowledge; to develop and use robust evidence and analysis; to challenge thinking; and to review effectiveness.<br/>In simple terms policy provides the route map to tackling issues. HSE is particularly well placed in terms of the three components of effective policy - “politics” “evidence” and “delivery”. Unlike most regulators and arms-length bodies HSE leads on policy development which draws directly on front line delivery expertise and intelligence; and we are also unusual in having our own world class science and insight capabilities.<br/>The challenge is to ensure we bring these components together to best effect to respond to new risk management and regulatory issues with effective innovative and proportionate approaches.<br/>Many of the articles in this Review relate to new and emerging technologies and the changing world of work and it is important to understand the risks these may pose and how they can be effectively controlled or how they themselves can contribute to improved health and safety in the workplace. Good policy development can support approaches to change that are proportionate relevant persuasive and effective. For example work described in these pages is: to help understand changing workplace exposures; to provide robust evidence to those negotiating alternatives to unduly prescriptive standards; to understand how best to influence duty<br/>holder behaviors in the changing world of work; to inform possible legislative changes to allow different modes of safe gas transmission; to change administrative processes for Appointed Doctors; and to support our position as a model modern regulator by further focusing our inspection activity where it matters most.<br/>The vital interface between HSE science and policy understand how best to influence duty holder behaviors in the changing world of work; to inform possible legislative changes to allow different modes of safe gas transmission; to change administrative processes for Appointed Doctors; and to support our position as a model modern regulator by further focusing our inspection activity where it matters most.<br/>We work well together and it is important we maintain this engagement as a conscious collaboration.

Numerical studies were conducted with the objective of gaining a better understanding of the consequences of potential explosion that could be associated with release of hydrogen in a confined and unconfined environment. This paper describes the work done by us in modelling explosion of accidental releases of hydrogen using our Fire Explosion Release Dispersion (FRED) software. CAM and SCOPE models in FRED is used for validation of congested/uncongested unconfined and congested/uncongested confined vapour cloud explosion respectively. In the first step CAM is validated against experiments of varying gas cloud size blockage ratio equivalence ratio of the mixture and blockage configuration. The model predictions of explosion overpressure are in good agreement with experiments. The results obtained from FRED i.e. overpressure as a function of distance match well in comparison to the experiments. In the second step SCOPE is validated against vented explosion experiments available in open literature. In general SCOPE reproduces the maximum overpressure within the factor of 2. Moreover it well predicts the trends of increase in overpressure with change in type of the fuel increase in number of obstacles blockage ratio and decrease in the vent size.

It is well-known that deflagration to detonation transition (DDT) may be a significant threat for hydrogen explosions. This paper presents a summary of the work carried out for the development of models in order to enable the industrial computational fluid dynamic (CFD) tool FLACS to provide indications about the possibility of a deflagration-to-detonation transition (DDT). The likelihood of DDT has been expressed in terms of spatial pressure gradients across the flame front. This parameter is able to visualize when the flame front captures the pressure front which is the case in situations when fast deflagrations transition to detonation. Reasonable agreement was obtained with experimental observations in terms of explosion pressures transition times and flame speeds for several practical geometries. The DDT model has also been extended to develop a more meaningful criterion for estimating the likelihood of DDT by comparison of the geometric dimensions with the detonation cell size. The conclusion from simulating these experiments is that the FLACS DPDX criterion seems robust and will generally predict the onset DDTs with reasonable precision including the exact location where DDT may happen. The standard version of FLACS can however not predict the consequences if there is DDT as only deflagration flames are modelled. Based on the methodology described above an approach for predicting detonation flames and explosion loads has been developed. The second part of the paper covers new paradigms associated with risk assessment of a hydrogen infrastructure such as a refueling station. In particular approaches involving one-to-one coupling between CFD and FEA modelling are summarized. The advantages of using such approaches are illustrated. This can have wide-ranging implications on the design of things like protection walls against hydrogen explosions.

This discussion session interrogated the current understanding of hydrogen embrittlement mechanisms in steels. This article is a transcription of the recorded discussion of ‘Hydrogen in steels’ at the Royal Society Scientific Discussion Meeting ‘The challenges of hydrogen and metals’ 16–18 January 2017.

The text is approved by the contributors. E.L.S. transcribed the session. M.P. assisted in the preparation of the manuscript

Link to document download on Royal Society Website 

According to European Directive 2014/94/EU hydrogen providers have the responsibility to prove that their hydrogen is of suitable quality for fuel cell vehicles. Contaminants may originate from hydrogen production transportation refuelling station or maintenance operation. This study investigated the probability of presence of the 13 gaseous contaminants (ISO 14687-2) in hydrogen on 3 production processes: steam methane reforming (SMR) process with pressure swing adsorption (PSA) chlor-alkali membrane electrolysis process and water proton exchange membrane electrolysis process with temperature swing adsorption. The rationale behind the probability of contaminant presence according to process knowledge and existing barriers is highlighted. No contaminant was identified as possible or frequent for the three production processes except oxygen (frequent for chlor-alkali membrane process) carbon monoxide (frequent) and nitrogen (possible) for SMR with PSA. Based on it a hydrogen quality assurance plan following ISO 19880-8 can be devised to support hydrogen providers in monitoring the relevant contaminants.

Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply e.g. as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system burner design and other boundary conditions these changes may cause higher combustion temperatures and laminar combustion velocities while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas these effects may cause risk of flashback reduced operational safety material deterioration higher nitrogen oxides emissions (NOx) and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.

This paper deals with site selection problems for hydrogen production plants and aims to propose a structural procedure for determining the most feasible sites. The study area is Adrar province Algeria which has a promising wind potential. The methodology is mainly composed of two stages: the first stage is to evaluate and select the best locations for wind-powered hydrogen production using GIS and MCDM technique. the AHP is applied to weigh the criteria and compute a LSI to evaluate potential sites and the second stage is applying different filtration constraints to select the suitable petrol stations for such hydrogen refuelling station modification. The result map showed that the entire Adrar province is almost suitable for wind-powered hydrogen production with varying suitability index. The LSI model groups sites into three categories: High suitable areas Medium suitable areas and Low suitable. As a result 2.95 % (12808.97 km2) of the study area has high suitability 54.59 % (236320.16 km2) has medium suitability 1.12 %(4842.94 km2) has low suitability and 41.34 % (178950.35 km2) of the study area is not suitable for wind hydrogen production. By applying the constraints about 4 stations are suitable for wind-powered hydrogen refuelling system retrofitting in Adrar province.

With government legislating for net-zero by 2050 what does this mean for UK energy markets and business models?<br/>Getting to net-zero will require economy-wide changes that extend well beyond the energy system leading to rapid and unprecedented change in all aspects of society.<br/>This report shines a light on the level of disruption that could be required by some sectors to meet net-zero targets. With many businesses making strong commitments to a net-zero carbon future the report highlights the stark future facing specific sectors. Some will need to make fundamental change to their business models and operating practices whilst others could be required to phase out core assets. Government may need to play a role in purposefully disrupting specific sectors to ensure the move away from high carbon business models facilitating the transition a zero-carbon economy. Sector specific impactsThe in-depth analysis presented in ‘Disrupting the UK energy systems: causes impacts and policy implications’ focuses on four key areas of the economy highlighting how they may need to change to remain competitive and meet future carbon targets.<br/>Heat: All approaches for heat decarbonisation are potentially disruptive with policymakers favouring those that are less disruptive to consumers. Since it is unlikely that rapid deployment of low carbon heating will be driven by consumers or the energy industry significant policy and governance interventions will be needed to drive the sustainable heat transformation.<br/>Transport: Following the ‘Road to Zero’ pathway for road transport is unlikely to be disruptive but it is not enough to meet our climate change targets. The stricter targets for phasing out conventional vehicles that will be required will lead to some disruption. Vehicle manufacturers the maintenance and repair sector and the Treasury may all feel the strain.<br/>Electricity: Strategies of the Big 6 energy companies have changed considerably in recent years with varying degrees of disruption to their traditional business model. It remains to be seen whether they will be able to continue to adapt to rapid change – or be overtaken by new entrants.<br/>Construction: To deliver low-carbon building performance will require disruptive changes to the way the construction sector operates. With new-build accounting for less than 1% of the total stock major reductions in energy demand will need to come through retrofit of existing buildings.<br/>The report identifies how policy makers plan for disruptions to existing systems. With the right tools and with a flexible and adaptive approach to policy implementation decision makers can better respond to unexpected consequences and ensure delivery of key policy objectives.

The amount of hydrogen gas generated from metal oxide materials based on a thermochemical water-splitting method gradually reduces as the surface of the metal oxide oxidizes during the hydrogen generation process. To regenerate hydrogen the oxygen reduction process of a metal oxide at high temperatures (1000–2500 °C) is generally required. In this study to overcome the problem of an energy efficiency imbalance in which the required energy of the oxygen reduction process for hydrogen regeneration is higher than the generated hydrogen energy we investigated the possibility of the oxygen reduction of a metal oxide with a low energy using microwave irradiation. For this purpose a macroporous nickel-oxide structure was used as a metal oxide catalyst to generate hydrogen gas and the oxidized surface of the macroporous nickel-oxide structure could be reduced by microwave irradiation. Through this oxidation reduction process ∼750 μmol g⁻¹ of hydrogen gas could be continuously regenerated. In this way it is expected that oxygen-enriched metal oxide materials can be efficiently reduced by microwave irradiation with a low power consumption of <∼4% compared to conventional high-temperature heat treatment and thus can be used for efficient hydrogen generation and regeneration processes in the future.

<br/>Our industry is beginning its journey on the transition to providing the world with sufficient sustainable affordable and low emission energy.<br/><br/>Decarbonisation is now a key priority. Steps range from reducing emissions from traditional oil and gas operations to investing in renewable energy and supplementing natural gas supplies with greener gasses such as hydrogen.<br/><br/>This paper looks at the role hydrogen could play in decarbonisation.

Seizing the clean growth opportunity. The move to cleaner economic growth is one of the greatest industrial opportunities of our time. This Strategy will ensure Britain is ready to seize that opportunity. Our modern Industrial Strategy is about increasing the earning power of people in every part of the country. We need to do that while not just protecting but improving the environment on which our economic success depends. In short we need higher growth with lower carbon emissions. This approach is at the heart of our Strategy for clean growth. The opportunity for people and business across the country is huge. The low carbon economy could grow 11 per cent per year between 2015 and 2030 four times faster than the projected growth of the economy as a whole. This is spread across a large number of sectors: from low cost low carbon power generators to more efficient farms; from innovators creating better batteries to the factories putting them in less polluting cars; from builders improving our homes so they are cheaper to run to helping businesses become more productive. This growth will not just be seen in the UK. Following the success of the Paris Agreement where Britain played such an important role in securing the landmark deal the transition to a global low carbon economy is gathering momentum. We want the UK to capture every economic opportunity it can from this global shift in technologies and services.<br/>Our approach to clean growth is an important element of our modern Industrial Strategy: building on the UK’s strengths; improving productivity across the country; and ensuring we are the best place for innovators and new businesses to start up and grow. A good example of this is offshore wind where costs have halved in just a few years. A combination of sustained commitment – across different Governments – and targeted public sector innovation support harnessing the expertise of UK engineers working in offshore conditions and private sector ingenuity has created the conditions for a new industry to flourish while cutting emissions. We need to replicate this success in sectors across our economy. This Strategy delivers on the challenge that Britain embraced when Parliament passed the Climate Change Act. If we get it right we will not just deliver reduced emissions but also cleaner air lower energy bills for households and businesses an enhanced natural environment good jobs and industrial opportunity. It is an opportunity we will seize.

From 2006 to 2009 INERIS alongside with CEA PSA PEUGEOT CITROËN and IRPHE were involved in a project called DRIVE. Its objective was to provide data on the whole reaction chain leading to a hydrogen hazard onboard a vehicle. Out of the three types of leakage identified by the consortium (permeation chronic and accidental) the chronic leakage taking place within the engine was judged to be more problematic since it can feature a high probability of occurrence and a significant release flow rate (up to 100 NL/min). Ignition tests carried out within a real and dummy engine compartment showed that pressure effects due to an explosion will be relatively modest provided that the averaged hydrogen concentration in this area is limited to 10% vol/vol which would correspond to a maximum release flow of 10 NL/min. This maximum concentration could be used as a threshold value for detection or as a target while designing the vehicle. Jet fire experiments were also conducted in the frame of the DRIVE project. It was found that pressure-relief devices (PRDs) might be unsuited to protect humans from the explosion of a tank caused by a bonfire. Other solutions are proposed in this paper.

The U.S. Department of Energy supports the implementation of hydrogen fuel cell technologies by providing hydrogen safety and emergency response training to first responders. A collaboration was formed to develop and deliver a one-day course that uses a mobile fuel cell vehicle (FCV) burn prop designed and built by Kidde Fire Trainers. This paper describes the development of the training curriculum including the design and operation of the FCV prop; describes the successful delivery of this course to over 300 participants at three training centers in California; and discusses feedback and observations received on the course. Photographs and video clips of the training sessions will be presented.

A large number of natural gas vehicles (NGV) with composite cylinders run in the world. In order to store hydrogen using the composite cylinder has also reached commercialization for the hydrogen fuel cell vehicle (FCV) which is been developing on ECO Energy. Under these increasing circumstances the most important issue is that makes sure of safety of the hydrogen composite cylinder. In case of the composite cylinder a standards to verify the safety of cylinders obey several country's standards. For NGV ISO 11439 has adopted as international standards but for FCV it has been still developing and there is only ISO/TS 15869 as international technical standards. In contents of international standards the fire test is the weakest part. The fire test is that the pressure relief valves (PRD) normally operate or not in order to prevent cylinders bursting when a vehicle is covered by fire. However with present standards there is no method to check the problem from vehicles in local flame. This study includes fire test results that have been performed to establish the fire-test standards.

The Sixth Carbon Budget report is based on an extensive programme of analysis consultation and consideration by the Committee and its staff building on the evidence published last year for our Net Zero advice. In support of the advice in this report we have also produced:

• A Methodology Report setting out the evidence and methodology behind the scenarios.
• A Policy Report setting out the changes to policy that could drive the changes necessary particularly over the 2020s.
• All the charts and data behind the report as well as a separate dataset for the Sixth Carbon Budget scenarios which sets out more details and data on the pathways than can be included in this report.
• A public Call for Evidence several new research projects three expert advisory groups and deep dives into the roles of local authorities and businesses.

Our recommended pathway requires a 78% reduction in UK territorial emissions between 1990 and 2035. In effect bringing forward the UK’s previous 80% target by nearly 15 years.

Low-carbon gases are indispensable to any energy system that is reliable clean affordable safe and is suited to spatial integration and zero-carbon hydrogen is a crucial link in that chain1. The most common element in the universe seems to have a highly bonding effect in the Netherlands – particularly as a result of the unique starting position of our country. This is made clear in the agreements of the National Climate Agreement which includes an ambitious target for hydrogen supported by a large and broad group of stakeholders. Industrial clusters and ports regard hydrogen as an indispensable part of their future and sustainability strategy. For the transport sector hydrogen (in combination with fuel cells) is crucial to achieving zero emissions transport. The agricultural sector has identified opportunities for the production of hydrogen and for its use. Cities regions and provinces are keen to get started on implementing hydrogen.<br/>The government embraces these targets and recognises the power of the framework for action demonstrated by so many parties. The focus on clean hydrogen in the Netherlands will lead to the creation of new jobs improvements to air quality and moreover is crucial to the energy transition.

Experiments on flame propagation regimes in a turbulent hydrogen jet with velocity and hydrogen concentration gradients have been performed at the FZK hydrogen test site HYKA. Horizontal stationary hydrogen jets released at normal and cryogenic temperatures of 290K and 80 and 35K with different nozzle diameters and mass flow rates in the range from 0.3 to 6.5 g/s have been investigated. Sampling probe method and laser PIV technique have been used to evaluate distribution of hydrogen concentration and flow velocity along and across the jet axis. High-speed photography (1000 fps) combined with a Background Oriented Schlieren (BOS) system was used for the visual observation of the turbulent flame propagation. In order to investigate different flame propagation regimes the ignition position was changed along the jet axis. It was found that the maximum flame velocity and pressure loads can only occur if the hydrogen concentration at the ignition point exceeds 11% of hydrogen in air. In this case the flame propagates in both directions up- and downstream the jet flow whereas in the opposite case the flame propagates only downstream. Such a behavior is consistent with previous experiments according to that the flame is able to accelerate effectively only if the expansion rate σ of the H2-air mixture is higher than a critical value σ* = 3.75 (like for the 11% hydrogen-air mixture). The measured data allow conservative estimates of the safety distance and risk assessment for realistic hydrogen leaks.

The review presented herein is regarding the stress corrosion cracking (SCC) phenomena of carbon steel pipelines affected by the corrosive electrolytes that comes from external (E) and internal (I) environments as well as the susceptibility and tensile stress on the SCC. Some useful tools are presented including essential aspects for determining and describing the E-SCC and I-SCC in oil and gas pipelines. Therefore this study aims to present a comprehensive and critical review of a brief experimental summary and a comparison of physicochemical mechanical and electrochemical data affecting external and internal SCC in carbon steel pipelines exposed to corrosive media have been conducted. The SCC hydrogen-induced cracking (HIC) hydrogen embrittlement and sulfide stress cracking (SSC) are attributed to the pH and to hydrogen becoming more corrosive by combining external and internal sources promoting cracking such as sulfide compounds acidic soils acidic atmospheric compounds hydrochloric acid sulfuric acid sodium hydroxide organic acids (acetic acid mainly) bacteria induced corrosion cathodic polarization among others. SCC growth is a reaction between the microstructural chemical and mechanical effects and it depends on the external and internal environmental sources promoting unpredictable cracks and fractures. In some cases E-SCC could be initiated by hydrogen that comes from the over-voltage during the cathodic protection processes. I-SCC could be activated by over-operating pressure and temperature at flowing media during the production gathering storage and transportation of wet hydrocarbons through pipelines. The mechanical properties related to I-SCC were higher in comparison with those reviewed by E-SCC suggesting that pipelines suffer more susceptibility to I-SCC. When a pipeline is designed the internal fluid being transported (changes of environments) and the external environment concerning SCC should be considered. This review offers a good starting point for newcomers into the field it is written as a tutorial and covers a large number of basic standards in the area.

In the development of hydrogen technology special attention is paid to the technical problems of hydrogen storage. One possible way is cryogenic storage in liquid form. Generally cryo-technical machines need components with interacting surfaces in relative motion such as bearings seals or valves which are subjected to extreme conditions. Materials of such systems have to be resistant to friction-caused mechanical deformation at the surface low temperatures and hydrogen environment. Since materials failure can cause uncontrolled escape of hydrogen new material requirements are involved for these tribo-systems in particular regarding operability and reliability. In the past few years several projects dealing with the influence of hydrogen on the tribological properties of friction couples were conducted at the Federal Institute for Materials Research and Testing (BAM) Berlin. This paper reports some  investigations carried out with polymer composites. Friction and wear were measured for continuous sliding and analyses of the worn surfaces were performed after the experiments. Tests were performed at room temperature in hydrogen as well as in liquid hydrogen.

In a near future with an increasing use of hydrogen as an energy vector gaseous hydrogen transport as well as high capacity storage may imply the use of high strength steel pipelines for economical reasons. However such materials are well known to be sensitive to hydrogen embrittlement (HE). For safety reasons it is thus necessary to improve and clarify the means of quantifying embrittlement. The present paper exposes the changes in mechanical properties of a grade API X80 steel through numerous mechanical tests i.e. tensile tests disk pressure test fracture toughness and fatigue crack growth measurements WOL tests performed either in neutral atmosphere or in high-pressure of hydrogen gas. The observed results are then discussed in front of safety considerations for the redaction of standards for the qualification of materials dedicating to hydrogen transport.

Computational Fluid Dynamics (CFD) tools have been increasingly employed for carrying out quantitative risk assessment (QRA) calculations in the process industry. However these tools must be validated against representative experimental data in order to have a real predictive capability. As any typical accident scenario is quite complex it is important that the CFD tool is able to predict combined release and ignition scenarios reasonably well. However this kind of validation is not performed frequently primarily due to absence of good quality data. For that reason the recent experiments performed by FZK under the HySafe internal project InsHyde (http://www.hysafe.org) are important. These involved vertically upwards hydrogen releases with different release rates and velocities impinging on a plate in two different geometrical configurations. The dispersed cloud was subsequently ignited and pressures recorded. These experiments are important not only for corroborating the underlying physics of any large-scale safety study but also for validating the important assumptions used in QRA. Blind CFD simulations of the release and ignition scenarios were carried out prior to the experiments to predict the results (and possibly assist in planning) of the experiments. The simulated dispersion results are found to correlate reasonably well with experimental data in terms of the gas concentrations. The overpressures subsequent to ignition obtained in the blind predictions could not be compared directly with the experiments as the ignition points were somewhat different but the pressure levels were found to be similar. Simulations carried out after the experiments with the same ignition position as those in the experiments compared reasonably well with the measurements in terms of the pressure level. This agreement points to the ability of the CFD tool FLACS to model such complex scenarios well. Nevertheless the experimental set-up can be considered to be small-scale and less severe than many accidents and real-life situations. Future large-scale data of this type will be valuable to confirm ability to predict large-scale accident scenarios.

Hydrogen has been extensively used in many industrial applications for more than 100 years including production storage transport delivery and final use. Nevertheless the goal of the hydrogen energy system implies the use of hydrogen as an energy carrier in a more wide scale and for a public not familiarised with hydrogen technologies and properties.<br/>The road to the hydrogen economy passes by the development of safe practices in the production storage distribution and use of hydrogen. These issues are essential for hydrogen insurability. We have to bear in mind that a catastrophic failure in any hydrogen project could damage the insurance public perception of hydrogen technologies at this early step of development of hydrogen infrastructures.<br/>Safety is a key issue for the development of hydrogen economy and a great international effort is being done by different stakeholders for the development of suitable codes and standards concerning safety for hydrogen technologies [1 2]. Additionally to codes and standards different studies have been done regarding safety aspects of particular hydrogen energy projects during the last years [3 4]. Most of such have been focused on hydrogen production and storage in large facilities transport delivery in hydrogen refuelling stations and utilization mainly on fuel cells for mobile and stationary applications. In comparison safety considerations for hydrogen storage in small or medium scale facilities as usual in hydrogen production plants from renewable energies have received relatively less attention.<br/>After a brief introduction to risk assessment for hydrogen facilities this paper reports an example of risk assessment of a small solar hydrogen storage system applied to the INTA Solar Hydrogen Production and Storage facility as particular case and considers a top level Preliminary Failure Modes and Effects Analysis (FMEA) for the identification of hazard associated to the specific characteristics of the facility.

The lay-out requirements developed for hydrogen systems operated in industrial environment are not suitable for the operating conditions specific to hydrogen refuelling stations (service pressure of up to 95 MPa facility for public use). A risk informed rationale has been developed to define and substantiate separation distance requirements in ISO 20100 Gaseous hydrogen – refuelling stations [1]. In this approach priority is given to preventing escalation of small incidents into majors ones with a focus on critical exposures such as places of occupancy (fuelling station retail shop) while optimizing use of the available space from a risk perspective a key objective for being able to retrofit hydrogen refuelling in existing stations.

This paper describes a methodology for simulating the structural response of vented enclosures during hydrogen deflagrations. The paper also summarises experimental results for the structural response of 20-foot ISO (International Organization for Standardization) containers in a series of vented hydrogen deflagration experiments. The study is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The project is funded by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 671461. The HySEA project focuses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of industrial applications. The structural response modelling involves one-way coupling of pressure loads taken either directly from experiments or from simulations with the computational fluid dynamics (CFD) tool FLACS to the non-linear finite element (FE) IMPETUS Afea Solver. The performance of the FE model is evaluated for a range of experiments from the HySEA project in both small-scale enclosures and 20-foot ISO containers. The paper investigates the sensitivity of results from the FE model to the specific properties of the geometry model. The performance of FLACS is evaluated for a selected set of experiments from the HySEA project. Furthermore the paper discusses uncertainties associated with the combined modelling approach.

Hydrogen-air mixtures are flammable in a wide range of compositions and have a low ignition energy compared to gaseous hydrocarbons. Due to its low density high buoyancy and diffusivity the mixing is strongly enhanced which supports distribution into large volumes if accidentally released. Economically valuable discontinuous transportation over large distances is only expected using liquid hydrogen (LH2). Releases of LH2 at its low temperature (20.3 K at 0.1 MPa) have additional hazards besides the combustible character of gaseous hydrogen (GH2). Hazard assessment requires simulation tools capable of calculating the pool spreading as well as the gas distribution for safety assessments of existing the future liquid hydrogen facilities. Evaluating possible risks the following process steps are useful:

• Possible accident release scenarios need to be identified for a given plant layout.
• Environmental boundary conditions such as wind conditions and humidity need to be identified and worst case scenarios have to be identified.
• A model approach based on this information which is capable of simulating LH2 releases vaporization rates and atmospheric dispersion of the gaseous hydrogen.
• Evaluate and verify safety distances identify new risks and/or extract certain design rules.

The process steps have been performed using the new validated 3D transient multiphase - multicomponent CFD model approach developed at Forschungszentrum Julich. A demonstration plant layout obtained from the IDEALHY project (Berstad et al.[1]) and two HAZID assessments (Hankinson et al.[2]) have been used for identifying a plant and a possible accident scenario. A general weather analysis at a possible location has been performed to identify weather conditions. Finally a full transient parameter calculation has been set up varying the LH2 release rate and the wind speed. The results have been analyzed and general conclusions have been derived.