Safety

To reveal the influence mechanisms of seasonal climatic factors (wind speed wind direction temperature) and leakage direction on hydrogen dispersion and explosion behavior from single-source leaks at typical risk locations (hydrogen storage tanks compressors dispensers) in hydrogen refueling stations (HRSs) this work established a full-scale 1:1 three-dimensional numerical model using the FLACS v22.2 software based on the actual layout of an HRS in Xichang Sichuan Province. Through systematic simulations of 72 leakage scenarios (3 equipment types × 4 seasons × 6 leakage directions) the coupled effects of climatic conditions equipment layout and leakage direction on hydrogen dispersion patterns and explosion risks were quantitatively analyzed. The key findings indicate the following: (1) Downward leaks (−Z direction) from storage tanks tend to form large-area ground-hugging hydrogen clouds representing the highest explosion risk (overpressure peak: 0.25 barg; flame temperature: >2500 K). Leakage from compressors (±X/−Z directions) readily affects adjacent equipment. Dispenser leaks pose relatively lower risks but specific directions (−Y direction) coupled with wind fields may drive significant hydrogen dispersion toward station buildings. (2) Southeast/south winds during spring/summer promote outward migration of hydrogen clouds reducing overall station risk but causing localized accumulation near storage tanks. Conversely north/northwest winds in autumn/winter intensify hydrogen concentrations in compressor and station building areas. (3) An empirical formula integrating climatic parameters leakage conditions and spatial coordinates was proposed to predict hydrogen concentration (error < 20%). This model provides theoretical and data support for optimizing sensor placement dynamically adjusting ventilation strategies and enhancing safety design in HRSs.

Hydrogen is a promising environmentally friendly fuel with the potential for zero-carbon emissions particularly in maritime applications. However owing to its wide flammability range (4–75%) significant safety concerns persist. In confined spaces hydrogen leaks can lead to explosions posing a risk to both lives and assets. This study conducts a numerical analysis to investigate hydrogen flow within hydrogen storage rooms aboard ships with the goal of developing efficient ventilation strategies. Through simulations performed using ANSYS-CFX this research evaluates hydrogen diffusion stratification and ventilation performance. A vertex angle of 120◦ at the ceiling demonstrated superior ventilation efficiency compared to that at 177◦ while air inlets positioned on side-wall floors or mid-sections proved more effective than those located near the ceiling. The most efficient ventilation occurred at a velocity of 1.82 m/s achieving 20 air exchanges per hour. These findings provide valuable insights for the design of safer hydrogen vessel operations.

Combustion of hydrogen-enriched natural gas is a valuable short-term strategy for reducing CO2 emissions from high temperature industrial heating. This paper presents several experiments on combustion characteristics and the formation of nitrogen oxides. The experiments included hydrogen contents up to 100% and fuel heat inputs up to 75 kW. Water-cooled lances were used to influence the furnace temperature. The analysis includes the distribution of furnace temperatures the composition of flue gas the cooling capacity of the lances under steady-state operating conditions and OH*-chemiluminescence imaging of the near burner region. The presented results demonstrate the dependence of furnace conditions and NOX formation on various factors such as different air inlet fluxes furnace temperature and fuel composition for constant heat inputs. Efficiency increased by up to 5.5% and significant changes in flame shaped along with a maximum increase in NOX emissions when comparing natural gas to hydrogen was measured at 167%.

Accidental hydrogen releases from pipelines pose significant risks particularly with the expanding deployment of hydrogen infrastructure. Despite this there has been a lack of thorough investigation into hydrogen leakage from pipelines especially under complex real-world conditions. This study addresses this gap by modeling hydrogen gas dispersion jet fires and explosions based on practical scenarios. Various factors influencing accident consequences such as leak hole size wind speed wind direction and trench presence were systematically examined. The findings reveal that both hydrogen dispersion distance and jet flame thermal radiation distance increase with leak hole size and wind speed. Specifically the longest dispersion and radiation distances occur when the wind direction aligns with the trench which is 110 m where the hydrogen concentration is 4% and 76 m where the radiation is 15.8 kW/m2 in the case of a 325 mm leak hole and wind under 10 m/s. Meanwhile pipelines lacking trenching exhibit the shortest distances 0.17 m and 0.98 m at a hydrogen concentration of 4% and 15.8 kW/m2 radiation with a leak hole size of 3.25 mm and no wind. Moreover under relatively higher wind speeds hydrogen concentration stratification occurs. Notably the low congestion surrounding the pipeline results in an explosion overpressure too low to cause damage; namely the highest overpressure is 8 kPa but this lasts less than 0.2 s. This comprehensive numerical study of hydrogen pipeline leakage offers valuable quantitative insights serving as a vital reference for facility siting and design considerations to eliminate the risk of fire incidents.

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces. The sudden failure of a pressurised hydrogen vessel was identified as a scenario of concern due to the severity of the consequences associated with such an event. In order to investigate this scenario experimentally HSE designed a bespoke and reusable ‘sudden release’ vessel. This paper presents an overview of the vessel and the results of a series of 13 tests whereby hydrogen was released from the bespoke vessel into a tunnel at pressures up to 65 MPa. The starting pressure and the volume of hydrogen in the vessel were altered throughout the campaign. Four of the tests also included congestion in the tunnel. The tests reliably autoignited. Overpressure measurements and flame arrival times measured with exposed-tip thermocouples enabled analysis of the severity of the events. A high-pressure fast-acting pressure transducer in the body of the vessel showed the pressure decay in the vessel which shows that 90% of the hydrogen was evacuated in between 1.8 and 3.2 ms (depending on the hydrogen inventory). Schlieren flow imagery was also used at the release point of the hydrogen showing the progression of the shock front following initiation of the tests. An assessment of the footage shows an estimated initial velocity of Mach 3.9 at 0.4 m from the release point. Based on this an ignition mechanism is proposed based upon the temperature behind the initial shock front.

A quantitative risk assessment on a representative liquid hydrogen storage system was performed to identify the main drivers of individual risk and provide a technical basis for revised separation distances for bulk liquid hydrogen storage systems in regulations codes and standards requirements. The framework in the Hydrogen Plus Other Alternative Fuels Risk Assessment Models (HyRAM+) toolkit was used and multiple relevant inputs to the risk assessment (e.g. system pipe size ignition probabilities) were individually varied. For each set of risk assessment inputs the individual risk as a function of the distance away from the release point was determined and the risk-based separation distance was determined from an acceptable risk criterion. These risk-based distances were then converted to equivalent leak size using consequence models that would result in the same distance to selected hazard criteria (i.e. extent of flammable cloud heat flux and peak overpressure). The leak sizes were normalized to a fraction of the flow area of the source piping. The resulting equivalent fractional hole sizes for each sensitivity case were then used to inform selection of a conservative fractional flow area leak size of 5% that serves as the basis for consequence-based separation distance calculations. This work demonstrates a method for using a quantitative risk assessment sensitivity study to inform the selection of a basis for determining consequence-based separation distances.

Hydrogen could gradually replace fossil fuels mitigating the human impact on the environment. However equipment exposed to hydrogen is subjected to damaging effects due to H2 absorption and permeation through metals. Hence inspection activities are necessary to preserve the physical integrity of the containment systems and the risk-based (RBI) methodology is considered the most beneficial approach. This review aims to provide relevant information regarding hydrogen embrittlement its effect on materials’ properties and the synergistic interplay of the factors influencing its occurrence. Moreover an overview of predictive maintenance strategies is presented focusing on the RBI methodology. A systematic review was carried out to identify examples of the application of RBI to equipment exposed to hydrogenated environments and to identify the most active research groups. In conclusion a significant lack of knowledge has been highlighted along with difficulties in applying the RBI methodology for equipment operating in a pure hydrogen environment.

The measurement of hydrogen concentration in fuel cell systems is an important prerequisite for the development of a control strategy to enhance system performance reduce purge losses and minimize fuel cell aging effects. In this perspective paper the working principles of hydrogen sensors are analyzed and their requirements for hydrogen control in fuel cell systems are critically discussed. The wide measurement range absence of oxygen high humidity and limited space turn out to be most limiting. A perspective on the development of hydrogen sensors based on palladium as a gas-sensitive metal and based on the organic magnetic field effect in organic lightemitting devices is presented. The design of a test chamber where the sensor response can easily be analyzed under fuel cell-like conditions is proposed. This allows the generation of practical knowledge for further sensor development. The presented sensors could be integrated into the end plate to measure the hydrogen concentration at the anode in- and outlet. Further miniaturization is necessary to integrate them into the flow field of the fuel cell to avoid fuel starvation in each single cell. Compressed sensing methods are used for more efficient data analysis. By using a dynamical sensor model control algorithms are applied with high frequency to control the hydrogen concentration the purge process and the recirculation pump.

Hydrogen is one of the most promising alternative sources to relieve the energy crisis and environmental pollution. Hydrogen can be stored as cryogenic compressed hydrogen (CcH2) to achieve high volumetric energy densities. Reliable safety codes and standards are needed for hydrogen production delivery and storage to promote hydrogen commercialization. Unintended hydrogen releases from cryogenic storage systems are potential accident scenarios that are of great interest for updating safety codes and standards. This study investigated the behavior of CcH2 releases and dispersion. The extremely low-temperature CcH2 jets can cause condensation of the air components including water vapor nitrogen and oxygen. An integral model considering the condensation effects was developed to predict the CcH2 jet trajectories and concentration distributions. The thermophysical properties were obtained from the COOLPROP database. The model divides the CcH2 jet into the underexpanded initial entrainment and heating flow establishment and established flow zones. The condensation effects on the heat transfer and flow were included in the initial entrainment and heating zones. The empirical coefficients in the integral model were then modified based on measured concentration results. Finally the analytical model predictions are shown to compare well with measured data to verify the model accuracy. The present study can be used to develop quantitative risk assessment models and update safety codes and standards for cryogenic hydrogen facilities.

Hydrogen leakage and explosion accidents have obvious dangers ambiguity of accident information and urgency of decision-making time. These characteristics bring challenges to the optimization of emergency alternatives for such accidents. Effective emergency decision making is crucial to mitigating the consequences of accidents and minimizing losses and can provide a vital reference for emergency management in the field of hydrogen energy. An improved VIKOR emergency alternatives optimization method is proposed based on the combination of hesitant triangular fuzzy set (HTFS) and the cumulative prospect theory (CPT) termed the HTFS-CPT-VIKOR method. This method adopts the hesitant triangular fuzzy number to represent the decision information on the alternatives under the influence of multi-attributes constructs alternatives evaluation indicators and solves the indicator weights by using the deviation method. Based on CPT positive and negative ideal points were used as reference points to construct the prospect matrix which then utilized the VIKOR method to optimize the emergency alternatives for hydrogen leakage and explosion accidents. Taking an accident at a hydrogen refueling station as an example the effectiveness and rationality of the HTFS-CPT-VIKOR method were verified by comparing with the existing three methods and conducting parameter sensitivity analysis. Research results show that the HTFS-CPT-VIKOR method effectively captures the limited psychological behavior characteristics of decision makers and enhances their ability to identify filter and judge ambiguous information making the decisionmaking alternatives more in line with the actual environment which provided strong support for the optimization of emergency alternatives for hydrogen leakage and explosion accidents.