Safety

Hydrogen is one of the important alternative fuels for future transportation. At the present stage research into hydrogen safety and designing risk mitigation measures are significant task. For compact storage of hydrogen in fuel cell vehicles storage of hydrogen under high pressure up to 40 MPa at refuelling stations is planned and safety in handling such high-pressure hydrogen is essential. This paper describes our experimental investigation into dispersion of high-pressure hydrogen gas which leaks through pinholes in the piping to the atmosphere. First in order to comprehend the basic behaviour of the steady dispersion of high-pressure hydrogen gas from the pinholes the time-averaged concentrations were measured. In our experiments initial release pressures of hydrogen gas were set at 20 MPa or 40 MPa and release diameters were in the range from 0.25 mm to 2 mm. The experimental results show that the hydrogen concentration along the axis of the dispersion plume can be expressed as a simple formula which is a function of the downwind distance X and the equivalent release diameter. This formula enables us to easily estimate the axial concentration (maximum concentration) at each downstream distance. However in order for the safety of flammable gas dispersion to be analyzed comparisons between time-averaged concentrations evaluated as above and lower flammable limit are insufficient. This is because even if time-averaged concentration is lower than the flammability limit instantaneous concentrations fluctuate and a higher instantaneous concentration occasionally appears due to turbulence. Therefore the time-averaged concentration value which can be used as a threshold for assessing safety must be determined considering concentration fluctuations. Once the threshold value is determined the safe distance from the leakage point can be evaluated by the above-mentioned simple formula. To clarify the phenomenon of concentration fluctuations instantaneous concentrations were measured with the fast-response flame ionization detector. A small amount of methane gas was mixed into the hydrogen as a tracer gas for this measurement. The relationship between the time-mean concentration and the occurrence probability of flammable concentration was analyzed. Under the same conditions spark-ignition experiments were also conducted and the relationship between the occurrence probability of flammable concentration and actual ignition probabilities were also investigated. The experimental results show that there is a clear correlation between the time-mean concentration the occurrence probability of flammable concentration flame length and occurrence probability of hydrogen flame.

Nowadays consumer demand for local and global environmental quality in terms of air pollution and in particular greenhouse gas emissions reduction may help to drive to the introduction of zero emission vehicles. At this regard the hydrogen technology appears to have future market valuablepotential. On the other hand the use of hydrogen vehicles which requires appropriate infrastructures for production storage and refuelling stages presents a lot of safety problems due to the peculiar chemicophysical hydrogen characteristics. Therefore safe at the most practices are essential for the successful proliferation of hydrogen vehicles. Indeed to avoid limit hazards it is necessary to implement practices that if early adopted in the development of a fuelling station project can allow very low environmental impact safety being incorporated in the project itself. Such practices generally consist in the integrated use of Failure Mode and Effect Analysis (FMEA) HAZard OPerability (HAZOP) and Fault Tree Analysis (FTA) which constitute well established standards in reliability engineering. At this regard however a drawback is the lack of experience and the scarcity of the relevant data collection. In this work we present the results obtained by the integrated use of FMEA HAZOP and FTA analyses relevant for the moment the high-pressure storage equipment in a hydrogen gas refuelling station. The study that is intended to obtain elements for improving safety of the system can constitute a basis for further more refined works.

Hydrogen technology requires efficient and safe hydrogen storage systems. For this purpose storage in solid materials such as high capacity complex hydrides is studied intensely. Independent from the actual material to be used eventually any tank design will combine nanoscale powders of highly reactive material with pressurized hydrogen gas and so far little is known about the behaviour of these mixtures in case of incidents. For a first evaluation of a complex hydride in case of a tank failure NaAlH4 (doped with Ti) was investigated in a small scale tank failure tests. 80-100 ml of the material were filled into a heat exchanger tube and sealed under argon atmosphere with a burst disk. Subsequently the NaAlH4 was partially desorbed by heating. When the powder temperature reached 130 °C and the burst disk ruptured at 9 bar hydrogen overpressure the behaviour of the expelled powder was monitored using a high speed camera an IR camera as well as sound level meters. Expulsion of the hydrogen storage material into (dry) ambient atmosphere yields a dust cloud of finely dispersed powder which does not ignite spontaneously. Similar experiments including an external source of ignition (spark / water reacting with NaAlH4) yield a flame of reacting powder. The intensity will be compared to the reaction of an equivalent amount of pure hydrogen.

This paper presents a compilation of the results supplied by HySafe partners participating in the Standard Benchmark Exercise Problem (SBEP) V2 which is based on an experiment on hydrogen combustion that is first described. A list of the results requested from participants is also included. The main characteristics of the models used for the calculations are compared in a very succinct way by using tables. The comparison between results together with the experimental data when available is made through a series of graphs. The results show quite good agreement with the experimental data. The calculations have demonstrated to be sensitive to computational domain size and far field boundary condition.

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

If the general public is to use hydrogen as a vehicle fuel customers must be able to handle hydrogen with the same degree of confidence and with comparable risk as conventional liquid and gaseous fuels. The hazards associated with jet releases from leaks in a vehicle-refuelling environment must be considered if hydrogen is stored and used as a high-pressure gas since a jet release in a confined or congested area could result in an explosion. As there was insufficient knowledge of the explosion hazards a study was initiated to gain a better understanding of the potential explosion hazard consequences associated with high-pressure leaks from refuelling systems. This paper describes two experiments with a dummy vehicle and dispenser units to represent refuelling station congestion. The first represents a ‘worst-case’ scenario where the vehicle and dispensers are enveloped by a 5.4 m x 6.0 m x 2.5 m high pre-mixed hydrogen-air cloud. The second is an actual high-pressure leak from storage at 40 MPa (400 bar) representing an uncontrolled full-bore failure of a vehicle refuelling hose. In both cases an electric spark ignited the flammable cloud. Measurements were made of the explosion overpressure generated its evolution with time and its decay with distance. The results reported provide a direct demonstration of the explosion hazard from an uncontrolled leak; they will also be valuable for validating explosion models that will be needed to assess configurations and conditions beyond those studied experimentally.

A new testing device for cyclic loading of specimens with a novel shape design is presented. The device was applied for investigations of fatigue of metallic specimens under pressurized hydrogen up to 300 bar at temperatures up to 200 °C. Main advantage of the specimen design is the very small amount of medium here hydrogen used for testing. This allows experiments with hazardous substances at lower safety level. Additionally no gasket for the load transmission is required. Woehler curves which show the influence of hydrogen on the fatigue behaviour of austenitic steel specimens at relevant service conditions in hydrogen powered engines are presented. Material and test conditions are in agreement with the cooperating industry.

Hydrogen from water electrolysis associated with renewable energies is one of the most attractive solutions for the green energy storage. To improve the efficiency and the safety of such stations some technological studies are still under investigation both on methods and materials. As methods control monitoring and diagnosis algorithms are relevant tools. These methods are efficient when they use an accurate mathematical model representing the real behaviour of hydrogen production system. This work focuses on the dynamical modelling and the monitoring of Proton Exchange Membrane (PEM) electrolyser. Our contribution consists in three parts: to develop an analytical dynamical PEM electrolyser model dedicated to the control and the monitoring; to identify the model parameters and to propose adequate monitoring tools. The proposed model is deduced from physical laws and electrochemical equations and consists in a steady-state electric model coupled with a dynamical thermal model. The estimation of the model parameters is achieved using identification and data fitting techniques based on experimental measurements. Taking into account the information given by the proposed analytical model and the experimentation data (temperature T voltage U and current I) given by a PEM electrolyser composed of seven cells the model parameters are identified. After estimating the dynamical model model based diagnosis approach is used in order to monitoring the PEM electrolyser and to ensure its safety. We illustrate how our algorithm can detect and isolate faults on actuators on sensors or on electrolyser system.<br/><br/>

Safety is an essential element for realizing the “hydrogen economy” – safe operation in all of its aspects from hydrogen production through storage distribution and use; from research development and demonstration to commercialization. As such safety is given paramount importance in all facets of the research development and demonstration of the U.S Department of Energy’s (DOE) Hydrogen Fuel Cells and Infrastructure Technologies (HFCIT) Program Office. The diversity of the DOE project portfolio is self-evident. Projects are performed by large companies small businesses DOE National Laboratories academic institutions and numerous partnerships involving the same. Projects range from research exploring advances in novel hydrogen storage materials to demonstrations of hydrogen refuelling stations and vehicles. Recognizing the nature of its program and the importance of safety planning DOE has undertaken a number of initiatives to encourage and shape safety awareness. The DOE Hydrogen Safety Review Panel was formed to bring a broad cross-section of expertise from the industrial government and academic sectors to help ensure the success of the program as a whole. The Panel provides guidance on safety-related issues and needs reviews individual DOE-supported projects and their safety plans and explores ways to bring learnings to broadly benefit the DOE program. This paper explores the approaches used for providing safety planning guidance to contractors in the context of their own (and varied) policies procedures and practices. The essential elements that should be included in safety plans are described as well as the process for reviewing project safety plans. Discussion of safety planning during the conduct of safety review site visits is also shared. Safety planning-related learnings gathered from project safety reviews and the Panel’s experience in reviewing safety plans are discussed.

This paper discusses the rationale structure and contents of the Canadian Hydrogen Safety Program developed by the Codes & Standards Working Group of the Canadian Transportation Fuel Cell Alliance consisting of representatives from industry academia government and regulators. The overall program objective is to facilitate acceptance of the products services and systems of the Canadian Hydrogen Industry by the Canadian Hydrogen Stakeholder Community to facilitate trade ensure fair insurance policies and rates ensure effective and efficient regulatory approval procedures and to ensure that the interests of the general public are accommodated. The Program consists of four projects including Comparative Quantitative Risk Assessment of Hydrogen and Compressed Natural Gas (CNG) Refuelling Stations; Computational Fluid Dynamics (CFD) Modelling Validation Calibration and Enhancement; Enhancement of Frequency and Probability Analysis and Consequence Analysis of Key Component Failures of Hydrogen Systems; and Fuel Cell Oxidant Outlet Hydrogen Sensor Project. The Program projects are tightly linked with the content of the IEA Task 19 Hydrogen Safety. The Program also includes extensive (destructive and non-destructive) testing of hydrogen components.