Safety

The differences in behaviour of hydrogen when compared to natural gas under deflagration and detonation scenarios are well known. The authors currently work in the area of fire and explosion analysis and have identified what they feel are potential gaps in the current Body of Knowledge (BOK) available to the sector. This is especially related to the behaviour around secondary shock formation and interactions with surrounding structures especially with ‘open’ structures such as steel frameworks typically seen in an offshore environment and practicable methods for determining debris formation and propagation. Whilst the defence sector has extensive knowledge in these areas this is primarily in the area of high explosives where the level of shocks observed is stronger than those resulting from a hydrogen detonation. This information would need to be reviewed and assessed to ensure it is appropriate for application in the hydrogen sector. Therefore with a focus on practicality the authors have undertaken a two-phase approach. The first phase involves carrying out a through literature search and discussions within our professional networks in order to ascertain whether there is a gap in the BOK. If good research guidance and tools to support this area of assessment already exist the authors have attempted to collate and consolidate this into a form that can be made more easily available to the community. Secondly if there is indeed a gap in the BOK the authors have attempted to ensure that all relevant information is collated to act as a reference and provide a consistent baseline for future research and development activities.

The National Renewable Energy Laboratory’s (NREL) Hydrogen Safety Research and Development (HSR&D) program in collaboration with the University of Maryland’s Systems Risk and Reliability Analysis Laboratory (SyRRA) are working to improve reliability and reduce risk in hydrogen systems. This approach strives to use quantitative data on component leaks and failures together with Prognosis and Health Management (PHM) and Quantitative Risk Assessment (QRA) to identify atrisk components reduce component failures and downtime and predict when components require maintenance. Hydrogen component failures increase facility maintenance cost facility downtime and reduce public acceptance of hydrogen technologies ultimately increasing facility size and cost because of conservative design requirements. Leaks are a predominant failure mode for hydrogen components. However uncertainties in the amount of hydrogen emitted from leaking components and the frequency of those failure events limit the understanding of the risks that they present under real-world operational conditions. NREL has deployed a test fixture the Leak Rate Quantification Apparatus (LRQA) to quantify the mass flow rate of leaking gases from medium and high-pressure components that have failed while in service. Quantitative hydrogen leak rate data from this system could ultimately be used to better inform risk assessment and Regulation Codes and Standards (RCS). Parallel activity explores the use of PHM and QRA techniques to assess and reduce risk thereby improving safety and reliability of hydrogen systems. The results of QRAs could further provide a systematic and science-based foundation for the design and implementation of RCS as in the latest versions of the NFPA 2 code for gaseous hydrogen stations. Alternatively data-driven techniques of PHM could provide new damage diagnosis and health-state prognosis tools. This research will help end users station owners and operators and regulatory bodies move towards risk-informed preventative maintenance versus emergency corrective maintenance reducing cost and improving reliability. Predictive modelling of failures could improve safety and affect RCS requirements such as setback distances at liquid hydrogen fueling sites. The combination of leak rate quantification research PHM and QRA can lead to better informed models enabling data-based decision to be made for hydrogen system safety improvements.

Hydrogen is an environmentally friendly source of renewable energy. Energy generation from hydrogen has not yet been widely commercialized due to issues related to risk management in its storage and transportation. In this paper the authors propose a hybrid multiple-criteria decision-making (MCDM)-based method to manage the risks involved in the storage and transportation of hydrogen (RSTH). First we identified the key points of the RSTH by examining the relevant literature and soliciting the opinions of experts and used this to build a prototype of its decision structure. Second we developed a hybrid MCDM approach called the D-ANP that combined the decision-making trial and evaluation laboratory (DEMENTEL) with the analytic network process (ANP) to obtain the weight of each point of risk. Third we used fuzzy evaluation to assess the level of the RSTH for Beijing China where energy generation using hydrogen is rapidly advancing. The results showed that the skills of the personnel constituted the most important risk-related factor and environmental volatility and the effectiveness of feedback were root factors. These three factors had an important impact on other factors influencing the risk of energy generation from hydrogen. Training and technical assistance can be used to mitigate the risks arising due to differences in the skills of personnel. An appropriate logistics network and segmented transportation for energy derived from hydrogen should be implemented to reduce environmental volatility and integrated supply chain management can help make the relevant feedback more effective.

Common root causes are often to be found in many if not most process safety incidents. Whilst largescale events are relatively rare such events can have devastating consequences. The subsequent investigations often uncover that the risks are rarely visible the direct causes are often hidden and that a ‘normalization of deviation’ is a common human characteristic. Process Safety Management (PSM) builds on the valuable lessons learned from past incidents to help prevent future recurrences. An understanding of how PSM originated and has evolved as a discipline over the past 200 years can be instructive when considering the safety implications of emerging technologies. An example is hydrogen production where risks must be effectively identified mitigated and addressed to provide safe production transportation storage and use .

Dilution ventilation is the current basis of safety following a flammable gas leak within a gas turbine enclosure and compliance requirements are defined for methane fuels in ISO 21789. These requirements currently define a safety criteria of a maximum flammable gas cloud size within an enclosure. The requirements are based on methane explosion tests conducted during a HSE Joint Industry Project which identified typical pressures associated with a range of gas cloud sizes. The industry standard approach is to assess the ventilation performance of specific enclosure designs against these requirements using CFD modelling. Gas turbine manufacturers are increasingly considering introducing hydrogen/methane fuel mixtures and looking towards operating with hydrogen alone. It is therefore important to review the applicability of current safety standards for these new fuels as the pressure resulting from a hydrogen explosion is expected to be significantly higher than that from a methane explosion. In this paper we replicate the previous methane explosion tests for hydrogen and hydrogen/methane fuel mixtures using the explosion modelling tool FLACS CFD. The results are used to propose updated limiting safety criteria for hydrogen fuels to support ventilation CFD analysis for specific enclosure designs. It is found that significantly smaller gas cloud sizes are likely to be acceptable for gas turbines fueled by hydrogen however significantly more hydrogen than methane is required per unit volume to generate a stoichiometric cloud (as hydrogen has a lower stoichiometric air fuel ratio than methane). This effect results in the total quantity of gas in the enclosure (and as such detectability of the gas) being broadly similar when operating gas turbines on hydrogen when compared to methane.

Hydrogen safety is an important topic for hydrogen energy application. Unintended hydrogen releases and combustions are potential accident scenarios which are of great interest for developing and updating the safety codes and standards. In this paper hydrogen releases and delayed ignitions were studied.

Equinor has in recent years focused on low carbon technologies in addition to conventional oil & gas technologies. Clear strategic directions have been set to demonstrate Equinor’s commitment to longterm value creation that supports the Paris Agreement. This includes acceleration of decarbonization by establishing a well-functioning market for carbon capture transport and storage (CCS) as well as development of competitive hydrogen-based value chains and solutions. The specific properties of hydrogen must be taken into account in order to ensure safe design and operation of hydrogen systems as these properties differ substantially from those of natural gas and other conventional oil & gas products. Development projects need to consider and mitigate the increased possibility of high explosion pressures or detonation if hydrogen releases accumulate in enclosed or congested areas. On the other hand hydrogen’s buoyant properties can be exploited by locating potential leak points in the open to avoid gas accumulation thereby reducing the explosion risk. The purpose of this paper is to introduce Equinor’s hydrogen-based value chain projects and present our approach to ensure safe and effective designs. Safety strategies constitute the basis for Equinor’s safety and risk management. The safety strategies describe the connection between the hazards and risk profiles on one hand and the safety barrier elements and their needed performance on the other as input to safe design. The safety strategies also form the basis for safe operation. Measures to control the risk through practical designs follow from these strategies.

In this study the combustion of submicron-sized Al particles in air was studied numerically with a particular focus on the effect of hydrogen addition. Oxidation of the Al particles and the interaction with hydrogen-related intermediates were considered by regarding them as liquid-phase molecules initially. Zero- and One-dimensional numerical simulations were then carried out to investigate the effect of the hydrogen addition on fundamental combustion characteristics of the Al flame by calculating properties such as ignition delay time and flame speed. Our attention was paid to how the hydrogen chemistry is coupled with the Al oxidation process. Numerical results show that the hydrogen addition generally reduces the reactivity of Al such that the flame speed and temperature decrease while it  can greatly shorten ignition delay times of the Al flame depending on initial temperatures.

In the framework of the HYTUNNEL-CS European project sponsored by FCH-JU a set of preliminary tests were conducted in a real tunnel in France. These tests are devoted to safety of hydrogen-fueled vehicles having a compressed gas storage and Temperature Pressure Release Device (TPRD). The goal of the study is to develop recommendations for Regulations Codes and Standards (RCS) for inherently safer use of hydrogen vehicles in enclosed transportation systems. Two scenarios were investigated (a) jet fire evolution following the activation of TPRD due to conventional fuel car fire and (b) explosion of compressed hydrogen tank. The obtained experimental data are systematically compared to existing engineering correlations. The results will be used for benchmarking studies using CFD codes. The hydrogen pressure range in these preliminary tests has been lowered down to 20MPa in order to verify the capability of various large-scale measurement techniques before scaling up to 70 MPa the subject of the second experimental campaign.

University of Pisa performed experimental tests in a 1m3 facility which shape and dimensions resemble a gas cabinet for the HySEA project founded by the Fuel Cells and Hydrogen 2 Joint Undertaking with the aim to conduct pre-normative research on vented deflagrations in real-life enclosures and containers used for hydrogen energy applications in order to generate experimental data of high quality. The test facility named Small Scale Enclosure (SSE) had a vent area of 042m2 which location could be varied namely on the top or in front of the facility while different types of vent were investigated. Three different ignition location were investigated as well and the range of Hydrogen concentration ranged between 10 and 18% vol. This paper is aimed to summarize the main characteristics of the experimental campaign as well as to present its results.