A comprehensive guide to Best Practice Guidelines (BPG) in numerical simulations for Fuel Cells and Hydrogen applications has been one of the main outputs of the SUSANA project. These BPG focus on the practical needs of engineers in consultancies and industry undertaking Computational Fluid Dynamics (CFD) simulations or evaluating CFD simulation results in support of hazard/risk assessments of hydrogen facilities, and the needs of regulatory authorities. This contribution presents the BPG document and the BPG application through a series of CFD benchmarking examples.

Catastrophic rupture of onboard hydrogen storage in a fire is a safety concern. Different passive, e.g. fireproofing materials, the thermally activated pressure relief device (TPRD), and active, e.g. initiation of TPRD by fire sensors, safety systems are being developed to reduce hazards from and associated risks of high-pressure hydrogen storage tank rupture in a fire. The probability of such low-frequency highconsequences event is a function of fire resistance rating (FRR), i.e. the time before tank without TPRD ruptures in a fire, the probability of TPRD failure, etc. This safety issue is “confirmed” by observed recently cases of CNG tanks rupture due to blocked or failed to operate TPRD, etc. The increase of FRR by any means decreases the probability of tank rupture in a fire, particularly because of fire extinction by first responders on arrival at an accident scene.

This study of socio-economic effects of safety applies a quantitative risk assessment (QRA) methodology to an example of hydrogen vehicles with passive tank protection system on roads in London.

The risk is defined here through the cost of human loss per fuel cell hydrogen vehicle (FCHV) fire accident and fatality rate per FCHV per year. The first step in the methodology is the consequence analysis based on validated deterministic engineering tools to estimate the main identified hazards: overpressure in the blast wave at different distances and the thermal hazards from a fireball in the case of catastrophic tank rupture in a fire. The population can be exposed to slight injury, serious injury and fatality after an accident. These effects are determined based on criteria by Health and Safety Executive (UK), and a cost metrics is applied to the number of exposed people in these three harm categories to estimate the cost per an accident. The second step in the methodology is either the frequency or the probability analysis. Probabilities of a vehicle fire and failure of the thermally activated pressure relief device are taken from published sources. A vulnerability probit function is employed to calculate the probability of emergency operations’ failure to prevent tank rupture as a function of a storage tank FRR and time of fire brigade arrival. These later results are integrated to estimate the tank rupture frequency and fatality rate. The risk is presented as a function of fire resistance rating.

The QRA methodology allows to calculate the cost of human loss associated with an FCHV fire accident and demonstrates how the increase of FRR of onboard storage, as a safety engineering measure, would improve socio-economics of FCHV deployment and public acceptance of the technology.

For the emerging hydrogen-powered vehicles, the safety concern is one of the most important barriers for their further development and commercialization. The safety of commercial natural gas vehicles has been well accepted and the total number of natural gas vehicles operating worldwide was approximately 23 million by November 2016. Hydrogen vehicles would be more acceptable for the general public if their safety is comparable to that of commercialized CNG vehicles. A comparison study is conducted to reveal the differences of hazard distances and accident durations between hydrogen vehicles and CNG vehicles during a representative accident in an open environment. The tank blowdown time for hydrogen and CNG are calculated separately to compare the accident durations. CFD simulations for real world situations are performed to study the hazard distances from impinging jet fires under vehicle. Results show that the release duration for CNG vehicle is over two times longer than that for hydrogen vehicle, indicating that CNG vehicle jet fire accident is more timeconsuming and firefighters have to wait a longer time before they can safely approach the vehicle. For both hydrogen vehicle and CNG vehicle, the longest hazard distance near the ground occur about 1 to 4 seconds after the initiation of the thermally-activated pressure relief devices. Afterwards the flames will shrink and the hazard distances will decrease. For firefighters with bunker gear, they must stand 6 m and 14 m away from the hydrogen vehicle and CNG vehicle, respectively. For general public, a perimeter of 12 m and 29 m should be set around the accident scene for hydrogen vehicle and CNG vehicle, respectively.

Vehicular use of hydrogen is the first attempt to apply hydrogen energy in consumers’ environment in large scale, though hydrogen has been widely used in industrial field for over one hundred years. The increasing number of hydrogen fuel cell vehicles has raised safety concerns in both public authorities and private bodies such as fire services and insurance companies. This paper analyzes typical accident progressions of hydrogen fuel cell vehicles in a road accident. Major hydrogen consequences including impinging jet fires and catastrophic tank ruptures are evaluated separately in terms of accident duration and hazard distances. Results show that in a 70 MPa fuel cell car accident, the hazards associated with hydrogen releases would normally last for no more than 1.5 minutes due to the empty of the tank. This indicates the first responders would be able to approach the vehicle, conservatively, approximate two minutes after hearing the hissing sound as the hydrogen hazards have been eliminated. For the safety of general public, a perimeter of 100 meters is suggested to be set in the accident scene if no hissing sound is heard. However, the perimeter can be reduced to 10 meters once the hissing sound of hydrogen release is observed. For the first responders, if there’s no sigh of hydrogen release, they should stand at least 10 m away from the burning car, otherwise their risk of fatality would be over 50% in case of catastrophic tank rupture. Furthermore, risks of fatalities, injuries, and damages are all quantified in financial terms to assess the impacts of the hypothetical accidents. Results show that costs of fatalities and injuries contribute most to the overall financial loss, indicating the insurance premium of fatalities and injuries should be set higher than that of property loss.

China has plenty of renewable energy like wind power and solar energy especially in the northwest part of the country. Due to the volatile and intermittent characters of the green powers, high penetration level of renewable resources could arise grid stabilization problem. Therefore electricity storage is considered as a solution and hydrogen energy storage is proposed. Instead of storing the electricity directly, it converts electricity into hydrogen and the energy in hydrogen will be released as needed from gas to electricity and heat. The transformed green power can be fed to the power grid and heat supply network. State Grid Corporation of China carried out its first hydrogen demonstration project. In the demonstration project, an alkaline electrolyzer and a PEM hydrogen fuel cell stack are decided as the hydrogen producer and consumer, respectively. Hydrogen safety issue is always of significant importance to secure the property. In order to develop a dedicated safety analysis method for hydrogen energy storage system in power industry, the risk analysis for the power-to-gas-topower&heat facility was made. The hazard and operability (HAZOP) study and the failure mode and effects analysis (FMEA) are performed sequentially to the installation, to identify the most problematic parts of the system in view of hydrogen safety and possible failure modes and consequences. At the third step, the typical hydrogen leak accident scenarios are simulated by using computational fluid dynamics (CFD) computer code. The resulted pressure loads of the possibly ignited hydrogen-air mixture in the facility container are estimated conservatively. Important safeguards and mitigation measures are proposed based on the three-stage risk and safety studies.

A methodology for explosion and fire risk analyses in enclosed rooms is presented. The objectives of this analysis are to accurately predict the risks associated with hydrogen leaks in maritime applications and to use the approach to provide decision support regarding design and risk-prevention and riskmitigating measures. The methodology uses CFD tools and simpler consequence models for ventilation, dispersion and explosion scenarios, as well as updated frequency for leaks and ignition. Risk is then efficiently calculated with a Monte Carlo routine capturing the transient behavior of the leak. This makes it possible to efficiently obtain effects of sensitivities and design options maintaining safety and reducing costs.

Nomograms for assessment of hazard distances from a blast wave, generated by a catastrophic rupture of stand-alone (stationary) and onboard compressed hydrogen cylinder in a fire are presented. The nomograms are easy to use hydrogen safety engineering tools. They were built using the validated and recently published analytical model. Two types of nomograms were developed – one for use by first responders and another for hydrogen safety engineers. The paper underlines the importance of an international effort to unify harm and damage criteria across different countries, as the discrepancies identified by the authors gave the expected results of different hazard distances for different criteria.

According to the Global technical regulation on hydrogen and fuel cell vehicles (FCV), fuel cell discharge system at the vehicle exhaust system`s point of discharge, the hydrogen concentration level shall not exceed 4 % average by volume during any moving three-second time interval during normal operation including start-up and shut down [1]. FC stack need to washout by the concentrated hydrogen as the purge gas and how to exhaust gas without exceeding 4 % is the most concerns. Also how to measure hydrogen pulse of millisecond in exhaust is also the rising up issue. In this paper, model of FCV hydrogen discharge system was composed and variety of simple experiments were carried out to control the H2 concentration and release. In the case which the semiconductor sensor with porous material (average size less than quench distance) were applied to check H2 concentration, the short pulse of high concentration of H2 in millisecond was hard to find. In this experiment, the simple exhaust gas model H2/N2 flow was used instead of Air/H2. In the exhaust gas test, experiment was conducted under the atmospheric condition in room temperature with small pressure difference and the fast solenoid valve to create quick hydrogen control. Most of the experiments except the turbulent flow experiments, laminar flow is expected to be dominated when steady state condition is satisfied but the most result discussed here is the measurement of H2 concentration during the start point at the time of discharge within seconds. The results showed when H2 was added to N2 flow, the boundary layer between N2 and H2 contained the high concentration of H2 at the initial wave front and decrease to reach steady state. This H2 pulse is typical in the FCV exhaust gas and topics of this paper

Portable H2 sensor was made by using mass spectrometer for the outside monitoring experiment: the leak test, the replacement test of gas pipe line, the combustion test, the explosion experiment, the H2 diffusion experiment and the recent issue of the exhaust gas of Fuel Cell Vehicle. In order to check the real time concentration of H2 in various conditions, even in the highly humid condition, the system volume of the sampling route was minimized with attaching the humidifier. Also to calibrate H2 concentration automatically, the specific concentration H2 small cylinder was mounted in the system. In the experiment, when H2 gas was introduced in the N2 flow or air in the tube or the high-pressure bottle, highly concentrated H2 phases were observed by this sensor without diffusion. This H2 sensor can provide the real time information of the hydrogen molecules and the clouds. The basic characterization of this sensor showed 0-100% H2 concentrations within 2ms. Our observation showed the size of the high concentration phase of H2 and the low concentration phase after mixing process. The mixed and unmixed H2, unintended concentration of cloud gas, the high speed small cluster of hydrogen molecules in purged gas were explored by this real time monitoring system.

Flame acceleration (FA) and explosion of hydrogen/air mixtures remain key issues for severe accident management in nuclear power plants. Empirical criteria were developed in the early 2000s by Dorofeev and colleagues, providing effective tools to discern possible FA or DDT (Deflagration-toDetonation Transition) scenarios. A large experimental database, composed mainly of middle-scale experiments in obstacle-laden ducts at atmospheric pressure condition, has been used to validate these criteria. However, during a severe accident, the high release rate of steam and non-condensable gases into the containment can result in pressure increase up to 5 bar abs. In the present work, the influence of the unburnt gas initial pressure on flame propagation mechanisms was experimentally investigated. Premixed hydrogen/air mixtures with H 2  close to 11% were considered. From the literature we know that these flames are supposed to accelerate up to Chapman-Jouguet deflagration velocity in long obstacle-laden tubes at initial atmospheric conditions. Varying the pressure in the fresh gas in the range 0.6-4 bar, no relevant effects on the flame acceleration phase were observed. However, as the initial pressure was increased, we observed a decrease in the flame velocity close to the end of the tube. The pressure increase due to the combustion reaction was found to be proportional to the initial pressure, as for the case of an adiabatic isochoric complete combustion.