Safety

Unstable hydrogen-air flame behavior randomities are important for industrial safety hydrogen infrastructure safety and nuclear power plant hydrogen safety problems. The paper is devoted to an experimental and theoretical study of the uncertainty in the acceleration of a premixed laminar unstable hydrogen flame. The results of experiments on spherical flame propagation in hydrogen-air mixtures with a hydrogen content of 10 to 60% are presented. The experiments were repeated up to 30 times in the same mixtures. A statistical analysis of the experimental results has been carried out. The scatter of the experimental data depending on the hydrogen content in the mixture was estimated. It was found to be between 8 to 17% for different mixtures with the same flame radius and mixture composition. Similar results were obtained using the numerical integration of the Sivashinsky equation of flame propagation.

In the context of a numerical investigation of thermal hazards from two under-expanded hydrogen jet fires results from a newly-developed thermal radiation module of the ADREA-HF computational fluid dynamics (CFD) code were validated against two physical experiments. The first experiment was a vertical under-expanded hydrogen jet fire at 170 bar with the objective of the numerical investigation being to capture the spatial distribution of the radial radiative heat flux at a given time instant. In the second case a horizontal under-expanded hydrogen jet fire at 340 bar was considered. Here the objective was to capture the temporal evolution of the radial radiative heat flux at selected fixed points in space. The numerical study employs the eddy dissipation model for combustion and the finite volume method (FVM) for the calculation of the radiative intensity. The FVM was implemented using a novel angular discretization scheme. By dividing the unit sphere into an arbitrary number of exactly equal angular control volumes this new scheme allows for more flexibility and efficiency. A demonstration of numerical convergence as a function the number of both spatial and angular control volumes was performed.

The NREL Hydrogen Sensor Laboratory was commissioned in 2010 as a resource for the national and international hydrogen community to ensure the availability and proper use of hydrogen sensors. Since then the Sensor Laboratory has provided unbiased verification of hydrogen sensor performance for sensor developers end-users and regulatory agencies and has also provided active support for numerous code and standards development organizations. Although sensor performance assessment remains a core capability the mission of the NREL Sensor Laboratory has expanded toward a more holistic approach regarding the role of hydrogen detection and its implementation strategy for both assurance of facility safety and for process control applications. Active monitoring for detection of unintended releases has been identified as a viable approach for improving facility safety and lowering setbacks. The current research program for the Sensor Laboratory addresses both conventional and advanced developing detection strategies in response to the emerging large-scale hydrogen markets such as those envisioned by H2@Scale. These emerging hydrogen applications may require alternative detection strategies that supplement and may ultimately supplant the use of traditional sensors for monitoring hydrogen releases. Research focus areas for the NREL Sensor Laboratory now encompass the characterization of released hydrogen behavior to optimize detection strategies for both indoor and outdoor applications assess advanced methods of hydrogen leak detection such as hydrogen wide area monitoring for large scale applications implement active monitoring as a risk reduction strategy to improve safety at hydrogen facilities and to provide continuing support of hydrogen safety codes and standards. In addition to assurance of safety detection will be critical for process control applications such as hydrogen fuel quality verification for fuel cell vehicle applications and for monitoring and controlling of hydrogen-natural gas blend composition.

This study presents a methodology of a quantitative risk assessment for the scenario of an onboard hydrogen storage tank rupture and tunnel fire incident. The application of the methodology is demonstrated on a road tunnel. The consequence analysis is carried out for the rupture of a 70 MPa 62.4-litre hydrogen storage tank in a fire that has a thermally activated pressure relief device (TPRD) failed or blocked during an incident. Scenarios with two states of charge (SoC) of the tank i.e. SoC = 99% and SoC = 59% are investigated. The risks in terms of fatalities per vehicle per year and the cost per incident are assessed. It is found that for the reduction in the risk with the hydrogen-powered vehicle in a road tunnel fire incident to the acceptable level of 10−5 fatality/vehicle/year the fireresistance rating (FRR) of the hydrogen storage tank should exceed 84 min. The FRR increase to this level reduces the societal risk to an acceptable level. The increase in the FRR to 91 min reduces the risk in terms of the cost of the incident to GBP 300 following the threshold cost of minor injury published by the UK Health and Safety Executive. The Frequency–Number (F–N) of the fatalities curve is developed to demonstrate the effect of mitigation measures on the risk reduction to socially acceptable levels. The performed sensitivity study confirms that with the broad range of input parameters including the fire brigade response time the risk of rupture of standard hydrogen tank-TPRD systems inside the road tunnel is unacceptable. One of the solutions enabling an inherently safer use of hydrogen-powered vehicles in tunnels is the implementation of breakthrough safety technology—the explosion free in a fire self-venting (TPRD-less) tanks.

Hydrogen is considered a promising energy carrier for a sustainable future when it is produced by utilizing renewable energy. Nowadays less than 4% of hydrogen production is based on electrolysis processes. Each component of a hydrogen energy system needs to be optimized to increase the operation time and system efficiency. Only in this way hydrogen produced by electrolysis processes can be competitive with the conventional fossil energy sources. As conventional electrolysers are designed for operation at fixed process conditions the implementation of fluctuating and highly intermittent renewable energy is challenging. Alkaline water electrolysis is a key technology for large-scale hydrogen production powered by renewable energy. At low power availability conventional alkaline water electrolysers show a limited part-load range due to an increased gas impurity. Explosive mixtures of hydrogen and oxygen must be prevented; thus a safety shutdown is performed when reaching specific gas contamination. The University of Pisa is setting up a dedicated laboratory including a 40-kW commercial alkaline electrolyser: the focus of the study is to analyze the safety of the electrolyser together with its performance and the real energy efficiency analyzing its operational data collected under different operating conditions affected by the unstable energy supply.

Hydrogen as energy carrier is referenced in French and European political strategies to realize the transition to low-carbon energy. In 2020 in France the government was launching a major investment plan amounting to 7.2 billion euros until 2030 to support the deployment of large-scale hydrogen technologies [1]. The implementation of this strategy should lead to the arrival of several new hydrogen systems that will need to be evaluated and certified regarding their compliance with safety requirements before being commercialized. Conformity assessment and certification play an important role to achieve a good safety level on the EU market for the protection of workers and consumers. It is a way for the manufacturer to prove that hazards have been identified and risks are managed and to demonstrate his commitment to safety that are key to access to the EU market. To assist manufacturers in identifying the applicable regulations standards and procedures for putting their product on the market Ineris elaborated a guidebook [2] with financial and technical support by ADEME the French Agency for Ecological Transition and France Hydrogen the French Association for Hydrogen and Fuel Cells. The preparation of this document also led to identifying gaps in the Regulations Codes and Standards (RCS) framework and necessary resources for the implementation of the conformity assessment procedures. This paper first describes the main regulatory procedures applicable for various types of hydrogen systems. Then describes the role of the actors involved in this process with a special focus on the French context. And finally focuses on some of the gaps that were identified and formulates suggestions to address them.

Hydrogen sensors especially those operating at high temperatures are essential tools for the emerging hydrogen economy. Monitoring hydrogen under process conditions to control the reactions for detecting confined species is crucial to the safe widespread use and public acceptance of hydrogen as fuel. Hydrogen sensors must have a sensitivity ranging from traces of hydrogen (parts per million (ppm)) up to levels near the lower explosive limit (LEL = 4% H2 in the air) for safety reasons. Furthermore they need to operate in cryogenic ambient and high-temperature environments. Herein emphasis is given to hydrogen sensors based on solid oxide electrolytes (operating at high temperatures) in particular oxygen ion and proton conductors. The review is devoted to potentiometric amperometric and combined amperometric-potentiometric hydrogen sensors. Experimental results already reported in the international literature are presented and analyzed to reveal the configuration principle of operation and the applied solid electrolytes and electrodes of the high-temperature hydrogen sensors. Additionally an amperometric sensor able to detect hydrogen and steam in atmospheric air through a two-stage procedure is presented and thoroughly discussed. The discussion reveals that high-temperature hydrogen sensors face different challenges in terms of the electrodes and solid electrolytes to be used depending on the operating principle of each sensor type.

Hydrogen gas storage place has been increasing daily because of its consumption. Hydrogen gas is a dream fuel of the future with many social economic and environmental benefits to its credit. However many hydrogen storage tanks exploded accidentally and significantly lost the economy infrastructure and living beings. In this study a protection wall under a worst-case scenario explosion of a hydrogen gas tank was analyzed with commercial software LS-DYNA. TNT equivalent method was used to calculate the weight of TNT for Hydrogen. Reinforced concrete and composite protection wall under TNT explosion was analyzed with a different distance of TNT. The initial dimension of the reinforced concrete protection wall was taken from the Korea gas safety code book (KGS FP217) and studied the various condition. H-beam was used to make the composite protection wall. Arbitrary-Lagrangian-Eulerian (ALE) simulation from LS-DYNA and ConWep pressure had a good agreement. Used of the composite structure had a minimum displacement than a normal reinforced concrete protection wall. During the worst-case scenario explosion of a hydrogen gas 300 kg storage tank the minimum distance between the hydrogen gas tank storage and protection wall should be 3.6 m.

As part of the United Nations Global Technical Regulation No. 13 (UN GTR #13 [1]) vehicle fire safety is validated using a localized and engulfing fire test methodology and currently updates are being considered in the on-going Phase 2 development stage. The GTR#13 fire test is designed to verify the performance of a hydrogen storage system of preventing rupture when exposed to service-terminating condition of fire situation. The test is conducted in two stages – localized flame exposure at a location most challenging for thermally-activated pressure relief device(s) (TPRDs) to respond for 10 min. followed by engulfing fire exposure until the system vents and the pressure falls to less than 1 MPa or until “time out” (30min. for light-duty vehicle containers and 60 min. for heavy-duty vehicle containers). The rationale behind this two-stage fire test is to ensure that even when fire sizes are small and TPRDs are not responding the containers have fire resistance to withstand or fire sensitivity to respond to a localized fire to avoid system rupture. In this study appropriate fire sizes for localized and engulfing fire tests in GTR#13 are evaluated by considering actual fire conditions in a hydrogen-powered electric city bus. Quantitative risk analysis is conducted to develop various fire accident scenarios including regular bus fire battery fire and hydrogen leak fire. Frequency and severity analyses are performed to determine the minimum fire size required in GTR#13 fire test to ensure hydrogen storage tank safety in hydrogen-powered electric city buses.

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.