Safety
H-Mat Hydrogen Compatibility of NBR Elastomers
Sep 2021
Publication
The H2@Scale program of the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office (HFTO) is supporting work on the hydrogen compatibility of polymers to improve the durability and reliability of materials for hydrogen infrastructure. The hydrogen compatibility program (H-Mat) seeks “to address the challenges of hydrogen degradation by elucidating the mechanisms of hydrogen-materials interactions with the goal of providing science-based strategies to design materials (micro)structures and morphology with improved resistance to hydrogen degradation.” Previous work on ethylene propylene diene indicated hydrogen interaction with plasticizer increased its migration to the surface and coalescing within the elastomer compound. New research on nitrile butadiene (NBR) has found hydrogen and pressure interactions with a series model rubber-material compounds to behave similarly in some compounds and improved in other compounds that is demonstrated through volume change and compression-set differences in the materials. Further studies were conducted using a helium-ion microscope (HeIM) which revealed significant morphological changes in the plasticizer-incorporating compounds after static exposure and pressure cycling as evidenced by time-of-flight secondary ion mass spectrometry. Additional studies using x-ray chromatography revealed that more micro-voids/-cracks developed after gas decompression in unfilled materials than in filled materials; transmission electron microscopy (TEM) probed at the nano-meter level showing change in filler distribution and morphology around Zinc-based particles.
Computational Fluid Dynamics Simulations of Hydrogen Releases and Vented Deflagrations in Large Enclosures
Nov 2019
Publication
This paper presents model predictions obtained with the CFD tool FLACS for hydrogen releases and vented deflagrations in containers and larger enclosures. The paper consists of two parts. The first part compares experimental results and model predictions for two test cases: experiments performed by Gexcon in 20-foot ISO containers (volume 33 m3 ) as part of the HySEA project and experiments conducted by SRI International and Sandia National Laboratories in a scaled warehouse geometry (volume 45.4 m3 ). The second part explores the use of the model system validated in the first part to accidental releases of hydrogen from forklift trucks inside a full-scale warehouse geometry (32 400 m3 ). The results demonstrate the importance of using realistic and reasonably accurate geometry models of the systems under consideration when performing CFD-based risk assessment studies. The discussion highlights the significant inherent uncertainty associated with quantitative risk assessments for vented hydrogen deflagrations in complex geometries. The suggestions for further work include a pragmatic approach for developing empirical correlations for pressure loads from vented hydrogen deflagrations in industrial warehouses with hydrogen-powered forklift trucks.
Knowledge and Technology Transfer via Publications, Patents, Standards: Exploring the Hydrogen Technological Innovation System
Nov 2022
Publication
Clean technologies play a crucial role in reducing greenhouse gas emissions and protecting the climate. Hydrogen is a promising energy carrier and fuel that can be used in many applications. We explore the global hydrogen technological innovation system (TIS) by analyzing the three knowledge and technology transfer channels of publications patents and standards. Since the adoption of hydrogen technologies requires trust in their safety this study specifically also focuses on hydrogen safety. Our results show that general and hydrogen safety research has increased significantly while patenting experienced stagnation. An analysis of the non-patent literature in safety patents shows little recognition of scientific publications. Similarly publications are under-represented in the analyzed 75 international hydrogen and fuel cell standards. This limited transfer of knowledge from published research to standards points to the necessity for greater involvement of researchers in standardization. We further derive implications for the hydrogen TIS and recommendations for a better and more impactful alignment of the three transfer channels.
Risk Assessment of a Hydrogen Refueling Station in an Urban Area
May 2023
Publication
After the Paris Agreement was signed in 2015 many countries worldwide focused on the hydrogen economy aiming for eco-friendly and renewable energy by moving away from the existing carbon economy which has been the primary source of global warming. Hydrogen is the most common element on Earth. As a light substance hydrogen can diffuse quickly; however it also has a small risk of explosion. Representative explosion accidents have included the Muskingum River Power Plant Vapor Cloud Explosion accident in 2007 and the Silver Eagle Refinery Vapor Cloud Explosion accident in 2009. In addition there was an explosion in a hydrogen tank in Gangneung Korea in May 2019 and a hydrogen refueling station (HRS) in Norway exploded in 2018. Despite this risk Korea is promoting the establishment of HRSs in major urban centers including downtown areas and public buildings by using the Regulatory Sandbox to install HRSs. This paper employed the Hydrogen Risk Assessment Model (HyRAM) of Sandia National Laboratories (SNL) a quantitative risk assessment (QRA) program specialized in hydrogen energy for HRSs installed in major urban hubs. A feasibility evaluation of the site conditions of an HRS was conducted using the French land use planning method based on the results obtained through evaluation using the HyRAM and the overpressure results of PHAST 8.0. After a risk assessment we confirmed that an HRS would be considered safe even if it was installed in the city center within a radius of influence of jet fires and overpressure.
Numerical Investigation on the Flame Structure and CO/NO Formations of the Laminar Premixed Biogas–Hydrogen Impinging Flame in the Wall Vicinity
Nov 2021
Publication
The near-wall flame structure and pollutant emissions of the laminar premixed biogashydrogen impinging flame were simulated with a detailed chemical mechanism. The spatial distributions of the temperature critical species and pollutant emissions near the wall of the laminar premixed biogas–hydrogen impinging flame were obtained and investigated quantitatively. The results show that the cold wall can influence the premixed combustion process in the flame front which is close to the wall but does not touch the wall and results in the obviously declined concentrations of OH H and O radicals in the premixed combustion zone. After flame quenching a high CO concentration can be observed near the wall at equivalence ratios (ϕ) of both 0.8 and 1.2. Compared with that at ϕ = 1.0 more unburned fuel is allowed to pass through the quenching zone and generate CO after flame quenching near the wall thanks to the suppressed fuel consumption rate near the wall and the excess fuel in the unburned gases at ϕ = 0.8 and 1.2 respectively. By isolating the formation routes of NO production it is found that the fast-rising trend of NO concentration near the wall in the post flame region at ϕ = 0.8 is attributed to the NO transportation from the NNH route primarily while the prompt NO production accounts for more than 90% of NO generation in the wall vicinity at ϕ = 1.2. It is thus known that thanks to the effectively increased surface-to-volume ratio the premixed combustion process in the downsized chamber will be affected more easily by the amplified cooling effects of the cold wall which will contribute to the declined combustion efficiency increased CO emission and improved prompt NO production.
Brief Review on High-Temperature Electrochemical Hydrogen Sensors
Dec 2022
Publication
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.
Analysis to Support Revised Distances between Bulk Liquid Hydrogen Systems and Exposures
Sep 2021
Publication
The minimum distances between exposures and bulk liquid hydrogen listed in the National Fire Protection Agency’s Hydrogen Technology Code NFPA 2 are based on historical consensus without a documented scientific analysis. This work follows a similar analysis as the scientific justification provided in NFPA 2 for exposure distances from bulk gaseous hydrogen storage systems but for liquid hydrogen. Validated physical models from Sandia’s HyRAM software are used to calculate distances to a flammable concentration for an unignited release the distance to critical heat flux values and the visible flame length for an ignited release and the overpressure that would occur for a delayed ignition of a liquid hydrogen leak. Revised exposure distances for bulk liquid hydrogen systems are calculated. These distances are related to the maximum allowable working pressure of the tank and the line size as compared to the current exposure distances which are based on system volume. For most systems the exposure distances calculated are smaller than the current distances for Group 1 they are similar for Group 2 while they increase for some Group 3 exposures. These distances could enable smaller footprints for infrastructure that includes bulk liquid hydrogen storage tanks especially when using firewalls to mitigate Group 3 hazards and exposure distances. This analysis is being refined as additional information on leak frequencies is incorporated and changes have been proposed to the 2023 edition of NFPA 2.
The NREL Sensor Laboratory: Status and Future Directions for Hydrogen Detection
Sep 2021
Publication
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.
Application of Pipeline QRA Methodologies to Hydrogen Pipelines in Support of the Transition to a Decarbonised Future
Sep 2021
Publication
Hydrogen is expected to play a key role in the decarbonised future of energy. For hydrogen distribution pipelines are seen as the main method for mass transport of hydrogen gas. To support the evaluation of risk related to hydrogen pipelines a revised QRA methodology is presented based on currently available and industry accepted guidance related to natural gas. The QRA approach is primarily taken from HSE UK’s MISHAP methodology [1]. The base methodology is reviewed and modifications suggested to adapt it for use with hydrogen gas transport. Compared to natural gas it was found that the escape distances for hydrogen (based on the degree of heat flux) were lower. However as for the overall risk for both individual and societal the case with hydrogen was more severe close to the pipeline. This was driven by the increased ignition probability of hydrogen. The approach may be used as part of the review and appraisal process of hydrogen projects
Hydrogen Blowdown Release Experiments at Different Temperatures in the Discha-facility
Sep 2021
Publication
In this work experiments on horizontal hydrogen jet releases from a 2.815 dm³ volume tank to the ambience are described. For the main experimental series tank valve and release line were cooled down to a temperature of approx. 80 K in a bath of liquid nitrogen. As a reference similar experiments were also performed with the uncooled tank at ambient temperature. The releases were carried out through four nozzles with different circular orifice diameters from 0.5 to 4 mm and started from initial tank pressures from 0.5 to 20 MPa (rel.). During the releases pressures and temperatures inside the vessel as well as inside the release line were measured. Outside the nozzle further temperature and hydrogen concentration measurements were performed along and besides the jet axis. The electrostatic field builtup in the jet was monitored using two field meters in different distances from the release nozzle and optical observation via photo and video-cameras was performed for the visualization of the H2-jet via the BOS-method. The experiments were performed in the frame of the EU-funded project PRESHLY in which several tests of this program were selected for a comparative computational study the results of which will also be presented at this conference. So on the one hand the paper gives a comprehensive description of the facility on the other hands it also describes the experimental procedure and the main findings.
Shock Tube Experiments on Flame Propagation Regimes and Critical Conditions for Flame Acceleration and Detonation Transition for Hydrogen-air Mixtures at Cryogenic Temperatures
Sep 2021
Publication
A series of more than 100 experiments with hydrogen-air mixtures at cryogenic temperatures have been performed in a shock tube in the frame of the PRESLHY project. A wide range of hydrogen concentrations from 8 to 60%H2 in the shock tube of the length of 5 m and 50 mm id was tested at cryogenic temperatures from 80 to 130K at ambient pressure. Flame propagation regimes were investigated for all hydrogen compositions in the shock tube at three different blockage ratios (BR) 0 0.3 and 0.6 as a function of initial temperature. Pressure sensors and InGaAs-photodiodes have been applied to monitor the flame and shock propagation velocity of the process. The experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. A critical expansion ratio for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criterion for smooth and obstructed channels was used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher compared to ambient temperature and the run-up-distance to detonation was several times shorter independent of lower chemical reactivity at cryogenic conditions.
Heat Transfer Models for Refueling Safety of Hydrogen Vehicle
Sep 2021
Publication
Due to the simple structure and quick refueling process of the compressed hydrogen storage tank it is widely used in fuel cell vehicles at present. However temperature rise may lead to a safety problem during charging of a compressed hydrogen storage tank. To ensure the refueling safety the thermal effects need to be studied carefully during hydrogen refueling process. In this paper based on the mass and energy balance equations a general heat transfer model for refueling process of compressed hydrogen storage tank is established. According to the geometric model of the tank wall structure we have built three lumped parameter models: single-zone (hydrogen) dual-zone (hydrogen and tank wall) and triple-zone (hydrogen tank wall liner and shell) model. These three lumped parameter models are compared with U.S. Naval gas charging model and SAE MC method based refueling model. Under adiabatic and diathermic conditions four models are built in Matlab/Simulink software to simulate the hydrogen refueling process under corresponding conditions. These four models are: single-zone singletemperature (hydrogen) dual-zone single-temperature (hydrogen) dual-zone dual-temperature (hydrogen and tank wall temperatures) and triple-zone triple-temperature (hydrogen tank wall liner and tank wall shell temperatures). By comparing the analytical solution and numerical solution the temperature rise of the compressed hydrogen storage tank can be described. The analytical and numerical solutions on the heat transfer during hydrogen refueling process will provide theoretical guidance at actual refueling station so as to improve the refueling efficiency and to enhance the refueling safety.
Safety and Other Considerations in the Development of a Hydrogen Fueling Protocol for Heavy-duty Vehicles
Sep 2021
Publication
Several manufacturers are developing heavy duty (HD) hydrogen stations and vehicles as zeroemissions alternatives to diesel and gasoline. In order to meet customer demands the new technology must be comparable to conventional approaches including safety reliability fueling times and final fill levels. For a large HD vehicle with a storage rated to 70 MPa nominal working pressure the goal to meet liquid fuel parity means providing 100 kg of hydrogen in 10 minutes. This paper summarizes the results to date of the PRHYDE project efforts to define the concepts of HD fueling which thereby lays the groundwork for the development of the safe and effective approach to filling these large vehicles. The project starts by evaluating the impact of several different assumptions such as the availability of static vehicle data (e.g. vehicle tank type and volume) and station data (e.g. expected station precooling capability) but also considers using real time dynamic data (e.g. vehicle tank gas temperature and pressure station gas temperature etc.) for optimisation to achieve safety and efficiency improvements. With this information the vehicle or station can develop multiple maps of fill time versus the hydrogen delivery temperature which are used to determine the speed of fueling. This will also allow the station or vehicle to adjust the rate of fueling as the station pre-cooling levels and other conditions change. The project also examines different steps for future protocol development such as communication of data between the vehicle and station and if the vehicle or station is controlling the fueling.
Performance of Hydrogen Storage Tanks of Type IV in a Fire: Effect of the State of Charge
Sep 2021
Publication
The use of hydrogen storage tanks at 100% of nominal working pressure (NWP) is expected only after refuelling. Driving between refuellings is characterised by the state of charge SoC <100%. There is experimental evidence that Type IV tanks tested in a fire at initial pressures below 1/3 NWP leaked without rupture. This paper aims at understanding this phenomenon. The numerical research has demonstrated that the heat transfer from fire through the composite overwrap at storage pressures below NWP/3 is sufficient to melt the polymer liner. This melting initiates hydrogen microleaks through the composite before it loses the load-bearing ability. The fire-resistance rating (FRR) is defined as the time to rupture in a fire of a tank without or with blocked thermally activated pressure relief device. The dependence of a FRR on the SoC is demonstrated for the tanks with defined material properties and volumes in the range of 36–244 L. A composite wall thickness variation is shown to cause a safety issue by reducing the tank’s FRR and is suggested to be addressed by tank manufacturers and OEMs. The effect of a tank’s burst pressure ratio on the FRR is investigated. Thermal parameters of the composite wall i.e. decomposition heat and temperatures are shown in simulations of a tank failure in a fire to play an important role in its FRR.
A Brief History of Process Safety Management
Sep 2021
Publication
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 .
Hydrogen Wide Area Monitoring of LH2 Releases at HSE for the PRESLHY Project
Sep 2021
Publication
The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to facilitate the safe use of hydrogen as an energy carrier. Empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring can elucidate the behavior of LH2 releases which can then be used to support and validate dispersion models. Hydrogen Wide Area Monitoring can be defined as the quantitative three-dimensional spatial and temporal profiling of planned or unintentional hydrogen releases. The NREL Sensor Laboratory developed a Hydrogen Wide Area Monitor (HyWAM) based upon a distributed array of hydrogen sensors. The NREL Sensor Laboratory and the Health and Safety Executive (HSE) formally committed to collaborate on profiling GH2 and LH2 releases which allowed for the integration of the NREL HyWAM into the HSE LH2 release behavior investigation supported by the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program. A HyWAM system was deployed consisting of 32 hydrogen measurement points and co-located temperature sensors distributed downstream of the LH2 release apparatus developed by HSE. In addition the HyWAM deployment was supported by proximal wind and weather monitors. In a separate presentation at this conference “HSE Experimental Summary for the Characterisation Dispersion and Electrostatic Hazards of LH2 for the PRESLHY Project” HSE researchers summarize the experimental apparatus and protocols utilized in the HSE LH2 releases that were performed under the auspices of PRESLHY. As a supplement to the HSE presentation this presentation will focus on the spatial and temporal behavior LH2 releases as measured by the NREL HyWAM. Correlations to ambient conditions such as wind speed and direction plume temperature and hydrogen concentrations will be discussed in addition to the design and performance of the NREL HyWAM and its potential for improving hydrogen facility safety.
Approaches and Methods to Demonstrate Repurposing of the UK's Local Transmission System (LTS) Pipelines for Transportation of Hydrogen
Sep 2021
Publication
Hydrogen has the potential as an energy solution to contribute to decarbonisation targets as it has the capability to deliver low-carbon energy at the scale required. For this to be realised the suitability of the existing natural gas pipeline networks for transporting hydrogen must be established. The current paper describes a feasibility study that was undertaken to assess the potential for repurposing the UK’s Local Transmission System (LTS) natural gas pipelines for hydrogen service. The analysis focused on SGN’s network which includes 3000 km of LTS pipelines in Scotland and the south of England. The characteristics of the LTS pipelines in terms of materials of construction and operation were first evaluated. This analysis showed that a significant percentage of SGN’s LTS network consists of lower strength grades of steel pipeline that operate at low stresses which are factors conducive to a pipeline’s suitability for hydrogen service. An assessment was also made of where existing approaches in pipeline operation may require modifications for hydrogen. The effects of changes in mechanical properties of steel pipelines on integrity and lifetime as a result of potential hydrogen degradation were demonstrated using fitness-for-purpose analysis. A review of pipeline risk assessment and Land-Use Planning (LUP) zone calculations for hydrogen was undertaken to identify any required changes. Case studies on selected sections of the LTS pipeline were then carried out to illustrate the potential changes to LUP zones. The work concluded with a summary of identified gaps that require addressing to ensure safe pipeline repurposing for hydrogen which cover materials performance inspection risk assessment land use planning and procedures.
Condensed Phase Explosions Involving Liquid Hydrogen
Sep 2021
Publication
Liquid hydrogen may have an important role in the storage and transportation of hydrogen energy. It may also provide the best option for some users of hydrogen energy notably the aviation sector. In the 1960’s liquid hydrogen spillages in open uncongested conditions sometimes produced violent condensed phase explosions as well as the familiar gas phase flash and sustained pool fire. Testing showed that burning mixtures of LH2 and solid oxygen/nitrogen readily transitioned to detonation for oxygen concentrations in the solid phase at or above 50%. Such explosive events have been observed in more recent research work on LH2 spillage and the pressure effects could be significant in some accident scenarios. There is a need to understand how solids are produced following spillage and what factors determine the level of oxygen enrichment. This paper describes the physical processes involved in the accumulation of solids during a horizontal discharge at ground level based on observations made in a recent HSE test that led to a condensed phase explosion. Areas where solids accumulated but remained in intimate contact with LH2 are identified. The paper also includes a thermodynamic and fluid mechanical analysis of the condensation process that includes the calculation of densities of mixtures of LH2 and air in different proportions. When the difference in flow speed between air and underlying LH2 is low a stable condensation layer can develop above the liquid where the temperature is just under the initial condensation point of air allowing sustained oxygen enrichment of condensate.
Observation of the Hydrogen Dispersion by Using Raman Scattering Measurement and Increase of Measurable Distance
Sep 2017
Publication
Preparing for the arrival of the hydrogen society it is necessary to develop suitable sensors to use hydrogen safely. There are many methods to know the hydrogen concentration by using conventional sensors but it is difficult to know the behavior of hydrogen gas from long distance. This study measured hydrogen dispersion by using Raman scattering light. Generally some delays occur when using conventional sensors but there are almost no delays by using the new Raman sensor. In the experiments 6mm & 1mm diameter holes are used as a spout nozzle to change initial velocities. To ensure the result a special sheets are used which turns transparent when it detected hydrogen and visualized the hydrogen behaviour. As a result the behaviour of the hydrogen gas in the small container was observed. In addition measurable distance is increased by the improvement of the device.
Effect of Wind on Cryogenic Hydrogen Dispersion from Vent Stacks
Sep 2021
Publication
Liquid hydrogen vent stacks often release hydrogen for example due to pressure relief from an underutilized tank boiling off hydrogen or after hydrogen delivery and transfer (trucks often depressurize through the tank vent stack to meet pressure regulations for on-road transport).<br/>A rapid release of cryogenic hydrogen through a vent stack will condense moisture from the entrained air forming a visible cloud. It is often assumed that the extent of the cold hydrogen is concurrent with the cloud. In this work a laser-based Raman scattering diagnostic was used to map out the hydrogen location during a series of vent stack release experiments. A description of the diagnostic instrument is given followed by a comparison of hydrogen signals to the visible cloud for releases through a liquid hydrogen vent stack. A liquid hydrogen pump was used to vary the flowrate of hydrogen through the vent stack and tests were performed under low and high wind conditions as well as low and high humidity conditions. The hydrogen was observed only where the condensed moisture was located regardless of the humidity level or wind. These measurements are being used to validate models such as those included in Sanda’s HyRAM toolkit and inform safety codes and standards.
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