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Risk quantification framework of hydride-based hydrogen storage systems for light-duty vehicles
Abstract
ABSTRACT
This study aims to develop a quantitative risk assessment (QRA) framework for on-board hydrogen storage systems in light-duty fuel cell vehicles, with focus on hazards from potential vehicular collision affecting hydride-based hydrogen storage vessels. Sodium aluminum hydride (NaAlH4) has been selected as a representative reversible hydride for hydrogen storage. Functionality of QRA framework is demonstrated by presenting a case study of a postulated vehicle collision (VC) involving the onboard hydrogen storage system. An event tree (ET) model is developed for VC as the accident initiating event. For illustrative purposes, a detailed FT model is developed for hydride dust cloud explosion as part of the accident progress. Phenomenologically-driven ET branch probabilities are estimated based on an experimental
program performed for this purpose. Safety-critical basic events (BE) in the FT model are determined using conventional risk importance measures. The Latin Hypercube sampling (LHS) technique has been employed to propagate the aleatory (i.e., stochastic) and epistemic (i.e., phenomenological) uncertainties associated with the probabilistic ET and FT models. Extrapolation of the proposed QRA framework and its core risk-informed insights to other candidate on-board reversible and off-board regenerable hydrogen storage systems could provide better understanding of risk consequences and mitigation options associated with employing this hydrogen-based technology in the transportation sector.
Keywords: Event tree; fault tree; on-board reversible; off-board regenerable; dust cloud explosion; importance measures
Supplementary resource (1)
... As part of quantifying the risks associated with on-board reversible and off-board regenerable hydrogen storage systems in LD-FCV, Khalil (2010d;2010e;2010f;2010g;2015) developed a roadmap (Fig. 3) that starts with qualitative risk assessment (QLRA) to identify potential failure modes and hazards of these systems. The primary QLRA methods include design and process failure modes & effects analysis (D-FMEA and P-FMEA) and hazard and operability (HAZOP) analysis. ...
... Input to QLRA can come from different sources such as expert opinion pooling (Khalil and Mosher, 2008), surrogate/ proxy data, field operating data, physics-based models, and test data. After the critical risks are identified using QLRA, quantitative risk assessment (QRA) methods and tools could be applied to quantify those critical risks and to assess the impact of proposed risk mitigation strategies (Khalil and Modarres, 2010g;Khalil, 2010a;2011b;2011c;2015). QRA methods include fault tree analysis (FTA) and event tree analysis (ETA). ...
... In the risk analysis performed by this author (Khalil, 2011d;2011e;2013b;2015), some of the postulated accident scenarios assume hydride storage vessel breach followed by contact of the spewed (dispersed) chunks of the stored hydride material with hot metal surfaces in the presence ...
The objective of this research is to examine the safety-related characteristics of candidate hydrogen storage materials being considered for use in light-duty fuel-cell vehicles (LD-FCV) under the U.S. Department of Energy (DOE) Hydrogen Program. This research aims to provide useful meaning to the general DOE safety target by establishing a link between the safety-related characteristics of candidate storage materials and satisfaction of DOE safety target. Accordingly, a science-based framework has been developed and consists of standardized materials tests (based on internationally accepted ASTM and United Nations testing protocols), novel risk mitigation strategies, and subscale system demonstration. The examined storage materials include NaAlH4, AlH3, 2LiBH4 + MgH2, 3Mg(NH2)2.8LiH, NH3BH3, and activated carbon (Maxsorb AX-21). The scope of safety tests covers conditions that the storage material may encounter during postulated accident scenarios such as dust cloud explosion, materials reactivity in air and other fluids, hot-surface contact, mechanical impact, and fast depressurization. The generated results uncovered potential fire and explosion risks under accidental conditions. The generated insights can be useful for assigning realistic probability values needed for quantifying risk scenarios, characterizing material’s hazard class, and supporting current and new hydrogen safety codes and standards. For risk mitigation, this study showed that powder compaction could be effective in suppressing pyrophoricity of hydride powders such as NaAlH4. Also, the study has experimentally demonstrated that adding (NH4)H2PO4 as a flame retardant to the hydride powder before compaction could suppress sensitivity of hydrides like NaAlH4 to ignite due to mechanical impact. The results also revealed that Maxsorb AX-21 to be a safer hydrogen storage medium compared to the examined hydrides which exhibited potential safety concerns under certain accident conditions.
... In Ref. [23] a risk assessment framework for onboard hydride-based hydrogen storage systems for light-duty vehicles was proposed and uncertainties involved were discussed. There are other hydrogen related risk assessment related studies including, but not limited to, an overview of risk assessment studies on hydrogen safety [24]; discussion on challenges towards hydrogen technology risk assessment [25,26]; risk assessment of hydrogen and CNG refuelling stations [27]; quantitative risk assessment of the mobile hydrogen refuelling station [28]; presenting a hydrogen risk assessment methodology [29]; , proposing and implementing a risk assessment methodology during the production of hydrogen in an oil refinery [30]; proposing and modelling of a risk matrix framework of cryogenic liquid hydrogen filling systems [31]; 3D risk management on hydrogen installations [32]; a grid-based risk assessment method in hydrogen refuelling stations [33] and performance-based design of refuelling stations [34]. ...
A quantitative risk assessment of onboard hydrogen-powered vehicle storage, exposed to a fire, is performed. The risk is defined twofold as a cost of human life per vehicle fire, and annual fatality rate per vehicle. The increase of fire resistance rating of the storage tank is demonstrated to drastically reduce the risk to acceptable level. Hazard distances are calculated by validated engineering tools for blast wave and fireball, which follow catastrophic tank rupture in a fire, act in all directions and have larger hazard distances compared to jet fire. The fatality cash value, probabilities of vehicle fire and failure of thermally activated pressure relief device are taken from published sources. A vulnerability probit function is employed to calculate probability of emergency operations' failure to control fire and prevent tank rupture. The risk is presented as a function of fire resistance rating of onboard storage.
... The hazard scenarios were determined using the HAZard Identification (HAZID) methodology. Khalil (2011Khalil ( , 2015 developed and quantified a fault tree (FT) model for gaseous H2 leakage (via permeation) through Type-III and Type-IV liners in on-board vehicular H2 storage systems. Galassi et al. (2012) described the main features of the Hydrogen Incidents and Accidents Database (HIAD) modules, namely, the Data Entry Module (DEM), the Data Retrieval Module (DRM), and the Data Analysis Module (DAM). ...
Leaks of flammable gases from containing systems pose safety concerns in many industrial settings. In this research, state-of-the-art visual flowcharting methodology is employed to develop a probabilistic model to quantify occupational risks of fire and explosion events initiated by leaks that ignite within enclosed spaces. In this model, leak initiation time and leak type (small, medium, or large) are selected based on user-specified probability distribution function and leak probability ranges, respectively. Other inputs to the model include probability distribution of time to failure of mechanical ventilation in the enclosed space, likelihood of presence of an ignition source with energy ≥ minimum ignition energy (MIE) of formed flammable gas cloud, probability of leak detection prior to ignition, and conditional probabilities of fires and explosions, given ignition. The model checks whether randomly-selected times of leak initiation and ventilation failure are within user-specified mission time. Number of personnel present near leak source is determined by a user-selected probability distribution. Uncertainties of input probabilities are propagated through the model using Monte Carlo sampling technique. Given occurrence of an undetected gaseous leak in conjunction with presence of an ignition source, ventilation failure, and presence of personnel close to the hazard source, the model calculates frequencies of risks of fire or explosion injuries, averaged over 10⁶ Monte Carlo trials per simulation run. Functionality of proposed model is demonstrated by a hydrogen refueling station (HRS) case study in which gaseous hydrogen is postulated to leak from its compressor system. Base case and worst case scenarios as well as sensitivity cases are considered and their simulation results show that, for these postulated scenarios, compressor's small H2 leaks (unlike medium and large leaks) pose intolerable occupational risk frequencies that exceed the acceptable risk level of 1.0E-4/year as well as NFPA's selected risk guideline of 2.0E-5/year which is driven by the comparative risk to gasoline stations. To mitigate predicted occupational risks to acceptable levels, safety control measures and best practices are recommended. The proposed model can be used as a training tool for first responders to fire and explosion events initiated by leaks of flammable gases. The model allows user-specified ‘what-if’ scenarios with or without risk mitigation measures. In addition to HRS, the model can be applied to a broad range of industrial applications such as natural gas refueling stations, indoor chiller systems which employ flammable refrigerants, and warehouses equipped with hydrogen-powered forklifts. Risk insights from this model's simulations can also support safety codes & standards and root cause investigations of industrial fire and explosion events.
Design failure modes, effects, and criticality analysis (d-FMECA) is a bottom-up, semi-quantitative risk assessment approach that is used by reliability engineers across all industries (nuclear, chemical, environmental, pharmaceuticals, aerospace, etc.) for identifying the effects of postulated components failure modes such as solenoid-operated valves (SOV), motor-operated valves (MOV), controllers, pumps, sensors of various types, printed circuit boards (PCBs). This research aims to develop a novel AI-augmented tool that guides, in real-time, the risk-analyst to a host of potential failure modes and their effects for each component contained in a bigger system. Through a user-friendly graphical interface and a robust statistical modeling backend, the AI-driven tool streamlines the risk assessment process by prompting the risk analyst to input a system’s name and subsequently generate an extensive array of failure modes and associated effects for each constituent component within the system. This AI-augmented tool allows the user to select either a simplified d-FMEA or a detailed d-FMECA for the system under investigation. This novel AI-driven tool offers significant effort and time savings in conducting d-FMECA, which is known to be a labor-intensive engineering task. In addition, this tool can be used for training risk and reliability professionals.
Like other energy carriers, hydrogen presents certain health and safety risks when used on a large scale. Safety considerations and incidents can slow, or even prevent, the deployment of a new energy technology if the risks are not well communicated and managed. CCUS is a salient example, and lithium-ion batteries have also faced concerns. On the other hand, the health and safety impacts of established energy products – gasoline, diesel, natural gas, electricity, coal – for consumers are familiar and rarely questioned, showing that risks – including flammability, presumed carcinogenicity and toxicity – can be managed to the satisfaction of users. As a light gas of small molecules, hydrogen requires special equipment and procedures to handle it. Hydrogen is so small it can diffuse into some materials, including some types of iron and steel pipes, and increase their chance of failure. It also escapes more easily through sealings and connectors than larger molecules, such as natural gas. Hydrogen is a non-toxic gas, but its high flame velocity, broad ignition range and low ignition energy make it highly flammable. This is partly mitigated by its high buoyancy and diffusivity, which causes it to dissipate quickly. It has a flame that is not visible to the naked eye and it iscolourless and odourless, making it harder for people to detect fires and leaks. There are already many decades of experience of using hydrogen industrially, including in large dedicated distribution pipelines. Protocols for safe handling at these sites are already in place, and they also exist for hydrogen refuelling infrastructure in site-specific forms. However, they remain complex and unfamiliar compared to those for other energy carriers. Widespread use in the energy system would bring new challenges. They would need further development and any public concerns would need to be alleviated.The health and safety considerations of most hydrogen-based fuels and feedstocks are familiar to the energy sector. The exceptions are ammonia and liquid organic hydrogen carriers, which have only recently been seriously considered for potential use in the energy system. Ammonia generally raises more health and safety considerations than hydrogen, and its use would probably need to continue to be restricted to professionally trained operators. It is highly toxic, flammable, corrosive, and escapes from leaks in gaseous form. However, unlike hydrogen, it has a pungent smell, making leaks easier to detect. It is also a precursor to air pollution. Like hydrogen, there is long experience of using ammonia industrially. It has been used as a refrigerant since the early nineteenth century and it has also been used in large-scale fertiliser production for over a century. Ammonia is routinely stored and transported, including in ocean-going tankers, and is sometimes injected directly into the soil in agriculture. Methylcyclohexane, a potential candidate LOHC, is flammable and dangerous to ingest, and its production requires toluene (which is toxic), but as a liquid, methylcyclohexane is less hazardous compared with gases, which can be inhaled. Dibenzyltoluene is considered to be an alternative LOHC option and is safer. Neither are currently handled in very large quantities, except in specific chemical facilities, but safe handling in pipelines or ships is not thought to pose a significant safety problem with appropriate controls in place.KeywordsHydrogen handlingSafetyStandardFireExplosionHazardsHydrogen embrittlementDesign conceptsMaterialsStrengthDuctility
This technical report on hydrogen safety (Task 37) of the Technical Collaboration Program (TCP), Internal Energy Agency (IEA) is comprised of five chapters as follows:
Chapter 1: Task goal and objectives
Chapter 2: Task member countries and organizational structure
Chapter 3: Task main achievements, deliverables, and safety knowledge dissemination
Chapter 4: Hydrogen safety and the path forward
Chapter 5: Task 37 key messages and recommendations
This technical report also has 3 appendices as follows:
Appendix A: Task 37 website
Appendix B: Hydrogen Safety Journal
Appendix C: Examples of Task 37 annual meetings
Task 37 provided the following key messages and recommendations for future hydrogen R&D activities:
1) Over its six-years duration, Task 37 provided key quantitative risk insights (both physics-based and probabilistic) to support the development of both new and revised hydrogen safety C&S (e.g., NFPA-2 and ISO standards).
2) Dr. Khalil emphasizes the importance of expanding the current scope of hydrogen safety beyond the hydrogen-powered light-duty electric vehicles (LDEV) application and H2 refueling stations. To this end, Dr. Khalil recommends expanding the scope of H2 safety to other applications such as maritime, commercial aviation (hybrid-electric & all-electric aircraft), power-to-gas (P2G), heavy-duty vehicles, trains, and H2 transport in long road tunnels and other confined-spaces such as garages. Accordingly, additional R&D efforts are needed to ensure the safety of emerging hydrogen-based technologies and associated infrastructures.
3) Bulk storage of hydrogen (whether as compressed gas or liquified) would require investigation of novel tanks design, materials selection, more robust risk mitigation and control methods, and H2 leakage detection devices.
4) Comprehensive safety-related research efforts are needed to address materials-compatibility issues associated with hydrogen.
5) Improved understanding of safety issues is needed with respect to separation distances (aka, setback distances or safety distances), underground and above-ground hydrogen storage, leakage of hydrogen from transport pipelines, injecting hydrogen gas in existing natural gas networks, risks associated with blending hydrogen with natural gas for domestic heating, etc.
6) Hydrogen production, transport & distribution, supply chains safety risks, infrastructure physical security and vulnerability assessment, as well as safety codes & standards continue to be central issues for achieving the desired economies of scale and reliable adoption of hydrogen-based technologies.
7) There is a need for harmonizing hydrogen safety codes & standards to remove (or at least lower) unnecessary regulatory barriers and to establish common standards that ensure safety in each stage of the hydrogen value chain. Achieving this goal will accelerate the deployment of at-scale hydrogen-based technologies.
As a concluding remark on what Task 37 of the Hydrogen Technical Collaboration Program (H2 TCP) has accomplished over the past six years, Dr. Khalil emphasizes that: We must continue to seize all emerging opportunities to demonstrate, via science-based methods, the safety of hydrogen-based technologies.
The author of this technical report is Dr. Y. F. Khalil, the Operating Agent (OA) and Manager of the Hydrogen Safety Task 37 (which started in January 2015 and ended in December 2021) of the International Energy Agency (IEA) headquartered in Paris, France.
Dr. Yehia F. Khalil delivered an invited lecture at the UK Research and Innovation - Hydrogen Experts Meeting, Department of Engineering Science, University of Oxford, UK. The meeting was held during the period May 22 – 23, 2018.
In this lecture, Dr. Khalil presented his portfolio of R&D related to sustainable hydrogen production, life cycle assessment (LCA), and life cycle impact assessment (LCIA). He also provided an overview of the Task 37 (Hydrogen Safety) which he manages for the International Energy Agency (IEA), Hydrogen Technical Collaboration Program (H2 TCP).
In this program, Dr. Khalil manages a portfolio of hydrogen R&D conducted by a group of H2 safety experts from several countries around the world including UK, France, Norway, Denmark, U.S., Canada, Japan, and China.
This technical report highlights key technical achievement, results, deliverables, and hydrogen safety knowledge dissemination of Task 37 (Hydrogen Safety) managed by Dr. Yehia F. Khalil for the International Energy Agency (IEA), Hydrogen Technical Collaboration Program (H2 TCP).
With the increasing interest for zero-emission vehicles, electric boats represent a growing area. Weight is a limiting factor for battery-powered boats, therefore, the use of fuel cell/battery systems is investigated. The present study examines the power requirements, the energy-storage solutions and the sustainability assessment of a light and fast rescue boat operating in the Swedish lake Barken. A weight-optimized hybrid fuel cell/battery system is presented. The results show that if the hydrogen storage is wisely selected, the weight of the hybrid system is significantly less than that of a battery system and can compete with an internal combustion engine system. The sustainability assessment highlights and compares the impact in terms of cost and emissions of the different energy storage solutions. The quantification of the emissions for the different energy systems under several scenarios shows a clear advantage for the electric solutions.
Risk assessment methods have been widely used in various industries, and they play a significant role in improving the safety performance of systems. However, the outcomes of risk assessment approaches are subject to uncertainty and ambiguity due to the complexity and variability of system behaviour, scarcity of quantitative data about different system parameters, and human involvement in the analysis, operation, and decision-making processes. The implications for improving system safety are slowly being recognised; however, research on uncertainty handling during both qualitative and quantitative risk assessment procedures is a growing field. This paper presents a review of the state of the art in this field, focusing on uncertainty handling in fault tree analysis (FTA) based risk assessment. Theoretical contributions, aleatory uncertainty, epistemic uncertainty, and integration of both epistemic and aleatory uncertainty handling in the scientific and technical literature are carefully reviewed. The emphasis is on highlighting how assessors can handle uncertainty based on the available evidence as an input to FTA.
Dr. Khalil, Operating Agent for the Hydrogen Safety Task of the International Energy Agency (IEA), discussed a framework comprised of standardized safety tests to assess the safe use of metal hydrides, chemical hydrides, and adsorbents as solid-state hydrogen storage media for on-board light-duty fuel cell vehicles. He also presented two baselines design for on-board hydrogen storage systems. The first design is for on-board reversible hydrogen storage and the second design is for off-board regenerable hydrogen storage.
Rhodium porphyrin catalyzed hydrogenation of the aliphatic carbon–carbon σ-bond of [2.2]paracyclophane with water has been examined with a variety of tetraarylporphyrins and axial ligands.
Solid-state hydrogen storage materials such as complex metal hydrides, chemical hydrides, and adsorbents are promising alternatives to the use of compressed hydrogen gas or liquefied hydrogen for on-board vehicular applications. However, acceptance by the general public to the use of hydrogen, in any of its on-board storage forms, as an energy carrier in the transportation sector requires assurance that this application is safe and poses no additional risks above the current risk acceptance criteria associated with use of gasoline/diesel in the transportation sector.
This research discusses the results of an experimental program covering materials reactivity tests, dust cloud combustion characterization tests, mechanical impact sensitivity tests, and material/hot surface contact tests. These tests were performed to identify safety-critical characteristics of selected solid-state hydrogen storage materials. Based upon the results of those tests, risk mitigation methods were proposed to eliminate or mitigate the identified risks. The effectiveness of the proposed risk mitigation methods was also examined. The insights gained from the experimental program could be useful to ongoing research efforts aimed at identifying the best hydrogen storage materials from a safety standpoint as well as supporting current and future risk-informed hydrogen safety standards such as NFPA-2, ISO, and IEC.
The findings of this research both experimental and probabilistic modeling is part of this Principal Investigator (PI) project funded by the U.S. Department of Energy.
Project title: Quantifying and Addressing the DOE Material Reactivity Requirements with Analysis and Testing of Hydrogen Storage Materials and Systems.
This paper discusses a behavioral-probabilistic approach for aggregating and updating experts' judgment to form posterior probabilities for uncertain events related to on-board hydrogen storage in in hydride materials. he proposed hybrid approach combines a Delphi process for expert judgment elicitation with Monte Carlo (MC) technique that generates a continuous probability distribution from elicited discrete probabilities after being combined using a conventional linear opinion pooling model. As new evidence becomes available, the aggregated probability can be Bayesian updated to generate a posterior probability distribution for the uncertain quantity or event of interest.
The functionality of the proposed approach is demonstrated using examples that draw upon a series of tests related to combustibility of lithium borohydride and magnesium hydride power mixtures. The examples show calculations of the posterior probability distribution using three different formats of experts' prior beliefs (discrete, beta, and histogram priors, respectively).
Statistical treatment of potential dependency among multiple experts' judgments is also presented. The insights of this study highlight the importance of expert judgment elicitation, and the proposed hybrid approach provides a framework for resolving uncertainties associated with risk analyses of on-board vehicular hydrogen storage systems.
This study focuses on risk analysis of on-board reversible hydrogen storage systems for hydrogen fuel cell vehicles (HFCV), and has two-fold objectives:
1) Demonstrate how SSCs compliance with applicable safety C&S can support qualitative and quantitative risk analyses.
2) Demonstrate how QLRA and QRA insights can support future risk-informed C&S development related to the on-board reversible hydrogen storage systems.
Risk Assessment and Safety Analysis for Commercial Nuclear Reactors (Chapter 16)
This chapter covers the following topics: 1) Status of operating commercial nuclear reactors in the United States, 2) NRC reactor licensing process and required permits, 3) An overview of probabilistic risk assessment, This includes Level-I PRA (front-end analysis), Level-II PRA (back-end analysis), and Level-III PRA (consequence analysis), and 4) Aleatory and epistemic uncertainties in PRA.
This study discusses benefits of using risk information derived from the plant-specific probabilistic risk assessment (PRA) to better manage the plant assets. A PRA-based methodology has been proposed to determine the sensitivity of the plant's economic risk to components reliability.
As a future extension of this work, the author will apply probabilistic and risk-informed approaches to enhance managing the assets process, namely: 1) use of decision analysis tools (such as decision trees, influence diagrams, and uncertainty analysis) to support the plant's staff's decision-making processes and 2) used of PRA to reduce current nuclear insurance premiums for the licensee's assets.
Vehicular on-board hydrogen storage using hydride and adsorbent materials is a growing fundamental research area that supports application of hydrogen technology in the transportation infrastructure. To realistically demonstrate hydrogen safety for vehicular applications, major uncertainties have to be resolved before critical risks can be quantified. Faced with the challenge of having to rely on very limited experimental data and an incomplete knowledgebase, hydrogen technology risk analysts must resort to pooling expert judgment to establish acceptable probabilities for the unknown quantities and phenomenology of interest.
This paper discusses a behavioral-probabilistic approach for aggregating and updating experts’ judgment to form posterior probabilities for uncertain events related to on-board hydrogen storage in hydride materials. The proposed hybrid approach combines a Delphi process for expert judgment elicitation with a Monte Carlo technique that generates a continuous probability distribution from elicited discrete probabilities after being combined using a conventional linear opinion pool model. As new evidence becomes available, the aggregated probability can be Bayesian updated to generate a posterior probability distribution for the uncertain quantity or event of interest. The functionality of the proposed approach is demonstrated using examples that draw upon a series of tests related to the combustibility of lithium borohydride and magnesium hydride powder mixtures. The examples show calculations of the posterior probability distribution using three different formats of experts’ prior beliefs (discrete, Beta, and histogram priors, respectively). Statistical treatment of potential dependency among multiple experts’ judgments is also presented. The insights of this study highlight the importance of expert judgment elicitation, and the proposed hybrid approach provides a framework for resolving uncertainties associated with risk analyses of on-board vehicular hydrogen storage systems.
Key Words and phrases: Bayesian update, expert judgment, hydrogen safety, linear pool model, subject matter expert.
The key technical target of this project is EH&S, having a focus on the safety sub-target with some consideration for toxicity. The technical target for safety is specified generally as “Meets or exceeds applicable standards.” For metal hydride, chemical hydride and adsorbent materials and systems, however, no such standards exist today. Furthermore, standards currently under development will be high-level in scope, primarily focused on systems and will not provide adequate guidance for evaluating and selecting viable candidate materials. As part of this effort, trade-offs will be evaluated between residual risks after mitigation and the two technical barriers:
(A) System Weight and Volume
(E) Charging/Discharging Rates
Solid-state hydrogen storage materials such as complex metal hydrides, chemical hydrides, and adsorbents are promising alternatives to the use of compressed hydrogen gas or liquefied hydrogen for on-board vehicular applications. However, acceptance by the general public to the use of hydrogen, in any of its on-board storage forms, as an energy carrier in the transportation sector requires assurance that this application is safe and poses no additional risks above the current risk acceptance criteria associated with use of gasoline/diesel in the transportation sector.
This research discusses the results of an experimental program covering materials reactivity tests, dust cloud combustion characterization tests, mechanical impact sensitivity tests, and material/hot surface contact tests. These tests were performed to identify safety-critical characteristics of selected solid-state hydrogen storage materials. Based upon the results of those tests, risk mitigation methods were proposed to eliminate or mitigate the identified risks. The effectiveness of the proposed risk mitigation methods was also examined. The insights gained from the experimental program could be useful to ongoing research efforts aimed at identifying the best hydrogen storage materials from a safety standpoint as well as supporting current and future risk-informed hydrogen safety standards such as NFPA-2, ISO, and IEC.
This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H-2) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H-0) that severity of deflagrations of H-2/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H-2/air containing the same H-2 concentrations as in the H-2/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (Delta P-MAX) and maximum rate of pressure rise ((dP/dt)(MAX)) of this hybrid mixture are greater than those corresponding to deflagrations of H-2/air mixtures for all the dust and H-2 concentrations being examined. The deflagration severity indices (K-st and ES) of the hybrid mixture containing 29 M01% H-2 are found to be greater than those of the H-2/air mixture containing 29 mol% H-2. Also, the minimum explosible concentration (MEC) of the hybrid mixture is lower than that of the AC dust in air only. The insights gained should lead to better realization of the severity of a postulated safety-significant accident scenario associated with on-board cryadsorption H-2 storage systems for fuel-cell (FC) powered light-duty vehicles. The identified insights could also be relevant to other industrial processes where combustible dusts are generated in the vicinity of solvent vapors. Moreover, these insights should be useful for supporting quantitative risk assessment (QRA) of on-board H-2 storage systems, designing improved safety measures for cryoadsorption H-2 storage tanks, and guiding H-2 safety standards and transportation regulations.
Experimental and theoretical studies were conducted to investigate the pyrophoricity and water-reactivity risks associated with employing sodium alanate (NaAlH4) complex metal hydride in on-board vehicular hydrogen (H2) storage systems. The ignition and explosivity of NaAlH4 upon exposure to oxidizers in air or water were attributed to the spontaneous formation of stable hydroperoxyl intermediates on the NaAlH4 surface and/or H2 production, as well as the large driving force for NaAlH4 conversion to favorable hydroxide products predicted by atomic and thermodynamic modeling. The major products from NaAlH4 exposure to air: NaAl(OH)4, gibbsite and bayerite Al(OH)3, and Na2CO3 observed by XRD, were identified to be formed by surface-controlled reactions. The reactivity risks were significantly minimized, without compromising de-/re-hydrogenation cyclability, by compacting NaAlH4 powder into wafers to reduce the available surface area. These core findings are of significance to risk mitigation and H2 safety code and standard development for the safe use of NaAlH4 for on-board H2 storage in light-duty vehicles.
Thesis research directed by: Reliability Engineering. Title from t.p. of PDF. Thesis (Ph. D.) -- University of Maryland, College Park, 2004. Includes bibliographical references. Text.
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6 The new data could be field/in-service failure data, experimental observations, or physics of failure (PoF) predictions. 7 From Table 2, the sum of end states mean probabilities of Seq-03
- Lb Lower
- Probability
LB ¼ lower bound probability.
6 The new data could be field/in-service failure data, experimental observations,
or physics of failure (PoF) predictions.
7 From Table 2, the sum of end states mean probabilities of Seq-03, Seq-05,
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