Safety
Assessing Damaged Pipelines Transporting Hydrogen
Jun 2022
Publication
There is worldwide interest in transporting hydrogen using both new pipelines and pipelines converted from natural gas service. Laboratory tests investigating the effect of hydrogen on the mechanical properties of pipeline steels have shown that even low partial pressures of hydrogen can substantially reduce properties such as reduction in area and fracture toughness and increase fatigue crack growth rates. However qualitative arguments suggest that the effects on pipelines may not be as severe as predicted from the small scale tests. If the trends seen in laboratory tests do occur in service there are implications for the assessment of damage such as volumetric corrosion dents and mechanical interference. Most pipeline damage assessment methods are semi-empirical and have been calibrated with data from full scale tests that did not involve hydrogen. Hence the European Pipeline Research Group (EPRG) commissioned a study to investigate damage assessment methods in the presence of hydrogen. Two example pipeline designs were considered both were assessed assuming a modern high performance material and an older material. From these analyses the numerical results show that the high toughness material will tolerate damage even if the properties are degraded by hydrogen exposure. However low toughness materials may not be able to tolerate some types of severe damage. If the predictions are realistic operators may have to repair more damage or reduce operating pressures. Furthermore damage involving cracking may not Page 2 of 22 satisfy the ASME B31.12 requirements for preventing time dependent crack growth. Further work is required to determine if the effects predicted using small scale laboratory test data will occur in practice.
Safety Compliance Verification of Fuel Cell Electric Vehicle Exhaust
Sep 2021
Publication
NREL has been developing compliance verification tools for allowable hydrogen levels prescribed by the Global Technical Regulation Number 13 (GTR-13) for hydrogen fuel cell electric vehicles (FCEVs). As per GTR-13 FCEV exhaust is to remain below 4 vol% H2 over a 3-second moving average and shall not at any time exceed 8 vol% H2 and that this requirement is to be verified with an analyzer that has a response time of less than 300 ms. To be enforceable a means to verify regulatory requirements must exist. In response to this need NREL developed a prototype analyzer that meets the GTR metrological requirements for FCEV exhaust analysis. The analyzer was tested on a commercial fuel cell electric vehicle (FCEV) under simulated driving conditions using a chassis dynamometer at the Emissions Research and Measurement Section of Environment and Climate Change Canada and FCEV exhaust was successfully profiled. Although the prototype FCEV Exhaust Analyzer met the metrological requirements of GTR-13 the stability of the hydrogen sensor was adversely impacted by condensed water in the sample gas. FCEV exhaust is at an elevated temperature and nearly saturated with water vapor. Furthermore condensed water is present in the form of droplets. Condensed water in the sample gas collected from FCEV exhaust can accumulate on the hydrogen sensing element which would not only block access of hydrogen to the sensing element but can also permanently damage the sensor electronics. In the past year the design of the gas sampling system was modified to mitigate against the transport of liquid water to the sensing element. Laboratory testing confirmed the effectiveness of the modified sampling system water removal strategy while maintaining the measurement range and response time required by GTR-13. Testing of the upgraded analyzer design on an FCEV operating on a chassis dynamometer is scheduled for the summer of 2021.
Development of Risk Mitigation Guidance for Hydrogen Sensor Placement Indoors and Outdoors
Sep 2021
Publication
Guidance on Sensor Placement remains one of the top priorities for the safe deployment of hydrogen and fuel cell equipment in the commercial marketplace. Building on the success of Phase l work reported at TCHS20l9 and published in TJHE this paper discusses the consecutive steps to further develop and validate such guidance for mechanically ventilated enclosures. The key step included a more in-depth analysis of sensitivity to variation of physical parameters in a small enclosure. and finally expansion of the developed approach to confined spaces in an outdoor environment.
An Investigation into the Volumetric Flow Rate Requirement of Hydrogen Transportation in Existing Natural Gas Pipelines and Its Safety Implications
Oct 2021
Publication
As an alternative to the construction of new infrastructure repurposing existing natural gas pipelines for hydrogen transportation has been identified as a low-cost strategy for substituting natural gas with hydrogen in the wake of the energy transition. In line with that a 342 km 3600 natural gas pipeline was used in this study to simulate some technical implications of delivering the same amount of energy with different blends of natural gas and hydrogen and with 100% hydrogen. Preliminary findings from the study confirmed that a three-fold increase in volumetric flow rate would be required of hydrogen to deliver an equivalent amount of energy as natural gas. The effects of flowing hydrogen at this rate in an existing natural gas pipeline on two flow parameters (the compressibility factor and the velocity gradient) which are crucial to the safety of the pipeline were investigated. The compressibility factor behaviour revealed the presence of a wide range of values as the proportions of hydrogen and natural gas in the blends changed signifying disparate flow behaviours and consequent varying flow challenges. The velocity profiles showed that hydrogen can be transported in natural gas pipelines via blending with natural gas by up to 40% of hydrogen in the blend without exceeding the erosional velocity limits of the pipeline. However when the proportion of hydrogen reached 60% the erosional velocity limit was reached at 290 km so that beyond this distance the pipeline would be subject to internal erosion. The use of compressor stations was shown to be effective in remedying this challenge. This study provides more insights into the volumetric and safety considerations of adopting existing natural gas pipelines for the transportation of hydrogen and blends of hydrogen and natural gas.
Protocol for Heavy-duty Hydrogen Refueling: A Modelling Benchmark
Sep 2021
Publication
For the successful deployment of the Heavy Duty (HD) hydrogen vehicles an associated infrastructure in particular hydrogen refueling stations (HRS) should be reliable compliant with regulations and optimized to reduce the related costs. FCH JU project PRHYDE aims to develop a sophisticated protocol dedicated to HD applications. The target of the project is to develop protocol and recommendations for an efficient refueling of 350 500 and 700 bar HD tanks of types III and IV. This protocol is based on modeling results as well as experimental data. Different partners of the PRHYDE European project are closely working together on this target. However modeling approaches and corresponding tools must first be compared and validated to ensure the high level of reliability for the modeling results. The current paper presents the benchmark performed in the frame of the project by Air Liquide Engie Wenger Engineering and NREL. The different models used were compared and calibrated to the configurations proposed by the PRHYDE project. In addition several scenarios were investigated to explore different cases with high ambient temperatures.
Safe Ventilation Methods against Leaks in Hydrogen Fuel Cell Rooms in Homes
Jul 2022
Publication
Hydrogen which has a high energy density and does not emit pollutants is considered an alternative energy source to replace fossil fuels. Herein we report an experimental study on hydrogen leaks and ventilation methods for preventing damage caused by leaks from hydrogen fuel cell rooms in homes among various uses of hydrogen. This experiment was conducted in a temporary space with a volume of 11.484 m3 . The supplied pressure leak-hole size and leakage amount were adjusted as the experimental conditions. The resulting hydrogen concentrations which changed according to the operation of the ventilation openings ventilation fan and supplied shutoff valve were measured. The experimental results showed that the reductions in the hydrogen concentration due to the shutoff valve were the most significant. The maximum hydrogen concentration could be reduced by 80% or more if it is 100 times that of the leakage volume or higher. The shutoff valve ventilation fan and ventilation openings were required to reduce the concentrations of the fuel cell room hydrogen in a spatially uniform manner. Although the hydrogen concentration in a small hydrogen fuel cell room for home use can rapidly increase a rapid reduction in the concentration of hydrogen with an appropriate ventilation system has been experimentally proven.
Review on the Hydrogen Dispersion and the Burning Behavior of Fuel Cell Electric Vehicles
Oct 2022
Publication
The development of a hydrogen energy-based society is becoming the solution for more and more countries. Fuel cell electric vehicles are the best carriers for developing a hydrogen energy-based society. The current research on hydrogen leakage and the diffusion of fuel cell electric vehicles has been sufficient. However the study of hydrogen safety has not reduced the safety concerns for society and government management departments concerning the large-scale promotion of fuel cell electric vehicles. Hydrogen safety is both a technical and psychological issue. This paper aims to provide a comprehensive overview of fuel cell electric vehicles’ hydrogen dispersion and the burning behavior and introduce the relevant work of international standardization and global technical regulations. The CFD simulations in tunnels underground car parks and multistory car parks show that the hydrogen escape performance is excellent. At the same time the research verifies that the flow the direction of leakage and the vehicle itself are the most critical factors affecting hydrogen distribution. The impact of the leakage location and leakage pore size is much smaller. The relevant studies also show that the risk is still controllable even if the hydrogen leakage rate is increased ten times the limit of GTR 13 to 1000 NL/min and then ignited. Multi-vehicle combustion tests of fuel cell electric vehicles showed that adjacent vehicles were not ignited by the hydrogen. This shows that as long as the appropriate measures are taken the risk of a hydrogen leak or the combustion of fuel cell electric vehicles is controllable. The introduction of relevant standards and regulations also indirectly proves this point. This paper will provide product design guidelines for R&D personnel offer the latest knowledge and guidance to the regulatory agencies and increase the public’s acceptance of fuel cell electric vehicles.
Numerical Study on Protective Measures for a Skid-Mounted Hydrogen Refueling Station
Jan 2023
Publication
Hydrogen refueling stations are one of the key infrastructure components for the hydrogen-fueled economy. Skid-mounted hydrogen refueling stations (SHRSs) can be more easily commercialized due to their smaller footprints and lower costs compared to stationary hydrogen refueling stations. The present work modeled hydrogen explosions in a skid-mounted hydrogen refueling station to predict the overpressures for hydrogen-air mixtures and investigate the protective effects for different explosion vent layouts and protective wall distances. The results show that the explosive vents with the same vent area have similar overpressure reduction effects. The layout of the explosion vent affects the flame shape. Explosion venting can effectively reduce the inside maximum overpressure by 61.8%. The protective walls can reduce the overpressures but the protective walls should not be too close to the SHRS because high overpressures are generated inside the walls due to the confined shock waves. The protective wall with a distance of 6 m can effectively protect the surrounding people and avoid the secondary overpressure damage to the container.
Numerical Modeling of a Moderate Hydrogen Leakage in a Typical Two-vented Fuel Cell Configuration
Sep 2021
Publication
Numerical results are presented from two direct numerical simulations (DNS) where a moderate hydrogen leakage is modeled in a typical two-vented fuel cell configuration. The study mimics one of the experimental investigations carried out on the 1 m3 enclosure with a leak flow rate of 10.4 Nl.min−1 [1]. The injection dimensionless Richardson number is at the order of unity and thus characterizes a plume flow which becomes turbulent due to gravitational accelerations. Two large exterior regions are added to the computational domain to model correctly the exchange between the in/out flows at both vents and the outer environment. Two meshes are used in this study; a first consisting of 250 million cells while the second has 2 billion cells to ensure the fine DNS resolution at the level of Kolmogorov and Batchelor length scales. The high performance computation (HPC) platform TRUST is employed where the computational domain is distributed up to 5.104 central processing unit (CPU) cores. A detailed description of the flow structure and the hydrogen dispersion is provided where the sharp effect of the cross-flow on the plume is analyzed. Comparisons versus the experimental measurements show a very good agreement where both the bi-layer Linden regime and the maximal concentration in the top homogeneous layer are correctly reproduced by the DNS. This result is extremely important and breaks the limitations shown previously with statistical RANS approaches and LES models. This study can be considered as a good candidate for any further improvements of the theoretical industrial plume models in general and for the estimation of the non-constant entrainment coefficient in particular.
Hydrogen Leakage Simulation and Risk Analysis of Hydrogen Fueling Station in China
Sep 2022
Publication
Hydrogen is a renewable energy source with various features clean carbon-free high energy density which is being recognized internationally as a “future energy.” The US the EU Japan South Korea China and other countries or regions are gradually clarifying the development position of hydrogen. The rapid development of the hydrogen energy industry requires more hydrogenation infrastructure to meet the hydrogenation need of hydrogen fuel cell vehicles. Nevertheless due to the frequent occurrence of hydrogen infrastructure accidents their safety has become an obstacle to large-scale construction. This paper analyzed five sizes (diameters of 0.068 mm 0.215 mm 0.68 mm 2.15 mm and 6.8 mm) of hydrogen leakage in the hydrogen fueling station using Quantitative Risk Assessment (QRA) and HyRAM software. The results show that unignited leaks occur most frequently; leaks caused by flanges valves instruments compressors and filters occur more frequently; and the risk indicator of thermal radiation accident and structure collapse accident caused by over-pressure exceeds the Chinese individual acceptable risk standard and the risk indicator of a thermal radiation accident and head impact accident caused by overpressure is below the Chinese standard. On the other hand we simulated the consequences of hydrogen leak from the 45 MPa hydrogen storage vessels by the physic module of HyRAM and obtained the ranges of plume dispersion jet fire radiative heat flux and unconfined overpressure. We suggest targeted preventive measures and safety distance to provide references for hydrogen fueling stations’ safe construction and operation.
Effect of Ignition Energy and Hydrogen Addition on Laminar Flame Speed, Ignition Delay Time, and Flame Rising Time of Lean Methane/Air Mixtures
Mar 2022
Publication
A series of experiments were performed to investigate the effect of ignition energy (Eig) and hydrogen addition on the laminar burning velocity (Su 0 ) ignition delay time (tdelay) and flame rising time (trising) of lean methane−air mixtures. The mixtures at three different equivalence ratios (φ) of 0.6 0.7 and 0.8 with varying hydrogen volume fractions from 0 to 50% were centrally ignited in a constant volume combustion chamber by a pair of pin-to-pin electrodes at a spark gap of 2.0 mm. In situ ignition energy (Eig ∼2.4 mJ ÷ 58 mJ) was calculated by integration of the product of current and voltage between positive and negative electrodes. The result revealed that the Su 0 value increases non-linearly with increasing hydrogen fraction at three equivalence ratios of 0.6 0.7 and 0.8 by which the increasing slope of Su 0 changes from gradual to drastic when the hydrogen fraction is greater than 20%. tdelay and trising decrease quickly with increasing hydrogen fraction; however trising drops faster than tdelay at φ = 0.6 and 0.7 and the reverse is true at φ = 0.8. Furthermore tdelay transition is observed when Eig > Eigcritical by which tdelay drastically drops in the pre-transition and gradually decreases in the post-transition. These results may be relevant to spark ignition engines operated under lean-burn conditions.
Hydrogen Non-premixed Combustion in Enclosure with One Vent and Sustained Release: Numerical Experiments
Sep 2013
Publication
Numerical experiments are performed to understand different regimes of hydrogen non-premixed combustion in an enclosure with passive ventilation through one horizontal or vertical vent located at the top of a wall. The Reynolds averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) model with a reduced chemical reaction mechanism is described in detail. The model is based on the renormalization group (RNG) k-ε turbulence model the eddy dissipation concept (EDC) model for simulation of combustion coupled with the 18-step reduced chemical mechanism (8 species) and the in-situ adaptive tabulation (ISAT) algorithm that accelerates the reacting flow calculations by two to three orders of magnitude. The analysis of temperature and species (hydroxyl hydrogen oxygen water) concentrations in time as well as the velocity through the vent shed a light on regimes and dynamics of indoor hydrogen fires. A well-ventilated fire is simulated in the enclosure at a lower release flow rate and complete combustion of hydrogen within the enclosure. Fire becomes under-ventilated at higher release flow rates with two different modes observed. The first mode is the external flame stabilised at the enclosure vent at moderate release rates and the second mode is the self-extinction of combustion inside and outside the enclosure at higher hydrogen release rates. The simulations demonstrated a complex reacting flow dynamics in the enclosure that leads to formation of the external flame or the self-extinction. The air intake into the enclosure at later stages of the process through the whole vent area is a characteristic feature of the self-extinction regime. This air intake is due to faster cooling of hot combustion products by sustained colder hydrogen leak compared to the generation of hot products by the ceasing chemical reactions inside the enclosure and hydrogen supply. In general an increase of hydrogen sustained release flow rate will change fire regime from the well-ventilated combustion within the enclosure through the external flame stabilised at the vent and finally to the self-extinction of combustion throughout the domain.
Numerical Study on Shockwave Attenuation by Water Mist in Confined Spaces
Sep 2021
Publication
Hydrogen safety has become the first consideration especially after fuel cell automobiles were pushed into commercial auto market. Tunnels are important parts of traffic infrastructure featured in confinement or semi-confinement. Hydrogen detonation is a potential accident scenario while hydrogen fuel cell vehicles are operated in a traffic tunnel with a confined space. Pressure shockwaves are mostly produced by hydrogen detonation and propagate along the tunnel. As a designed safety measure water mist injection is hopefully to mitigate the pressure loads of such shocks. To model the interaction between shockwaves and water droplets a droplet breakup model has been developed for the COM3D code which is a highly validated three-dimensional hydrogen explosion simulation code. By using the model the hydrogen detonation shockwave propagation in confined volumes is simulated in the study. The attenuation effects of water mist on the pressure shocks in the simulations are elaborated and discussed based on the simulation results.
Hydrogen Generation on Orkney: Integrating Established Risk Management Best Practice to Emerging Clean Energy Sector
Sep 2021
Publication
The European Marine Energy Centre’s (EMEC) ITEG project (Integrating Tidal Energy into the European Grid) funded by Interreg NWE combines a tidal energy and hydrogen production solution to address grid constraints on the island of Eday in Orkney. The project will install a 0.5MW electrolyser at EMEC’s existing hydrogen production plant. EMEC and Risktec collaboratively applied best practice risk assessment and management techniques to assess and manage hydrogen safety. Hazard identification (HAZID) workshops were conducted collaboratively with design engineers through which a comprehensive hazard register was developed. Risktec applied bowtie analysis to each major accident hazard identified from the hazard register via virtual workshop with design engineers. The bowties promoted a structured review of each hazard’s threat and consequence identifying and reviewing the controls in place against good practice standards. The process revealed some recommendations for further improvement and risk reduction exemplifying a systematic management of risks associated with hydrogen hazards to as low as reasonably practicable (ALARP). Hardware based barriers preventing or mitigating loss of control of these hazards were logged as safety critical elements (SCE) and procedural barriers as safety critical activities (SCA). To ensure that all SCEs and SCAs identified through the risk assessment process are managed throughout the facility’s operational lifetime a safety management system is created giving assurance of overall safety management system continued effectiveness. The process enables the demonstration that design risks are managed to ALARP during design and throughout operational lifetime. More importantly enabling ITEG to progress to construction and operation in 2021.
Assessment and Lessons Learnt from HIAD 2.0 – Hydrogen Incidents and Accidents Database
Sep 2019
Publication
The Hydrogen Incidents and Accidents Database (HIAD) is an international open communication platform collecting systematic data on hydrogen-related undesired events (incidents or accidents). It was initially developed in the frame of the project HySafe an EC co-funded NoE of the 6th Frame Work Programme by the Joint Research Centre of the European Commission (EC-JRC) and populated by many HySafe partners. After the end of the project the database has been maintained and populated by JRC with publicly available events.<br/>Starting from June 2016 JRC has been developing a new version of the database (HIAD 2.01). With the support of the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) the structure of the database and the web-interface have been redefined and simplified resulting in a streamlined user interface compared to the previous version of HIAD. The new version is mainly focused to facilitate the sharing of lessons learnt and other relevant information related to hydrogen technology; the database is publicly released and the events are anonymized. The database currently contains over 250 events. It aims to contribute to improve the safety awareness fostering the users to benefit from the experiences of others as well as to share information from their own experiences.<br/>The FCH 2 JU launched the European Hydrogen Safety Panel (EHSP2) initiative in 2017. The mission of the EHSP is to assist the FCH 2 JU at both programme and project level in assuring that hydrogen safety is adequately managed and to promote and disseminate hydrogen safety culture within and outside of the FCH 2 JU programme. Composed of a multidisciplinary pool of experts – 16 experts in 2018 - the EHSP is grouped in small ad-hoc working groups (task forces) according to the tasks to be performed and the expertise required. In 2018 Task Force 3 (TF3) of the ESHP has encompassed the analysis of safety data and events contained in HIAD 2.0 operated by JRC and supported by the FCH 2 JU. In close collaboration with JRC the EHSP members have systematically reviewed more than 250 events.<br/>This report summarizes the lessons learnt stemmed from this assessment. The report is self-explanatory and hence includes brief introduction about HIAD 2.0 the assessment carried out by the EHSP and the results stemmed from the joint assessment to enable new readers without prior knowledge of HIAD 2.0 to understand the rationale of the overall exercise and the lessons learnt from this effort. Some materials have also been lifted from the joint paper between JRC and EHSP which will also be presented at the International Conference on Hydrogen Safety (ICHS 2019) to provide some general and specific information about HIAD 2.0.
Numerical Prediction of Lean Premixed Hydrogen Deflagrations in Vented Vessels
Sep 2021
Publication
In water-cooled nuclear power plants hydrogen gas can be generated by various mechanisms during an accident. In case combustion of the resulting hydrogen-air mixture within the facility occurs existing containment structures may be compromised and excessive radio-active material can be released to the environment. Thus an improved understanding of the propagation of lean hydrogen deflagrations within buildings and structures is essential for the development of appropriate accident management strategies associated with these scenarios. Following the accident in Fukushima Japan the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes in both closed and vented vessels has become more widespread. In this study a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in vented vessels. The LES methodology makes use of a flamelet- or progress-variable-based combustion model coupled with an empirical burning velocity model (BVM) an anisotropic block-based adaptive mesh refinement (AMR) strategy an accurate finite-volume numerical scheme and a mesh independent subfilter-scale (SFS) model. Several different vessel and vent sizes and configurations are considered herein. The LES predictions are compared to experimental data obtained from the Large-Scale Vented Combustion Test Facility (LSVCTF) of the Canadian Nuclear Laboratories (CNL) with both quiescent and turbulent initial conditions. Following descriptions of the LES models LES results for both variable chamber sizes and single- and double-vent cases are presented to illustrate the capabilities of the proposed computational approach. In particular the predicted time histories of pressure as well as the maximum overpressure achieved within the vessels and combustion compartments are compared to those from the LSVCTF experiments. The influences of the modelled ignition process initial turbulence and mesh resolution on the LES results are also discussed. The findings highlight the potential and limitations of the proposed LES approach for accurately describing lean premixed hydrogen deflagrations within vented vessels.
Experimental Study on Flame Characteristics of Cryogenic Hydrogen Jet Fire
Sep 2021
Publication
In this work cryogenic hydrogen fires at fixed pressures and various initial temperatures were investigated experimentally. Flame length width heat fluxes and temperatures in down-stream regions were measured for the scenarios with 1.6-3 mm jet nozzle 106 to 273 K 2-5 barabs. The results show that the flame size is related to not only the jet nozzle diameter but also the release pressure and initial temperature. The correlations of normalized flame length and width are proposed with the stagnation pressure and the ratio of ambient and stagnation temperatures. Under constant pressure the flame size total radiative power and radiation fraction increase with the decrease of temperature due to lower choked flow velocity and higher density of cryogenic hydrogen. The correlation of radiation fraction proposed by Molina et al. at room temperature is not suitable to predict the cryogenic hydrogen jet fires. Based on piecewise polynomial law
Fuel-scale Tunnel Experiments for Fuel Cell Hydrogen Vehicles: Gas Dispersion
Sep 2021
Publication
In the framework of the HYTUNNEL-CS European project sponsored by FCH-JU a set of preliminary tests were conducted in a real tunnel in France. These tests are devoted to safety of hydrogen-fueled vehicles having a compressed gas storage and Temperature Pressure Release Device (TPRD). The goal of the study is to develop recommendations for Regulations Codes and Standards (RCS) for inherently safer use of hydrogen vehicles in enclosed transportation systems. In these preliminary tests the helium gas has been employed instead of hydrogen. Upward and downward gas releases following by TPRD activation has been considered. The experimental data describing local behavior (close to jet or below the chassis) as well as global behavior at the tunnel scale are obtained. These experimental data are systematically compared to existing engineering correlations. The results will be used for benchmarking studies using CFD codes. The hydrogen pressure range in these preliminary tests has been lowered down to 20MPa in order to verify the capability of various large-scale measurement techniques before scaling up to 70MPa the subject of the second campaign.
Safety Assessment of Hydrogen Jet Fire Scenarios within Semi-Confined Spaces
Jan 2023
Publication
Hydrogen fuel cell vehicle (HFCV) technology poses great promise as an alternative to significantly reduce the environmental impact of the transport sector’s emissions. However hydrogen fuel cell technology is relatively new therefore confirmation of the reliability and safety analysis is still required particularly for fire scenarios within confined spaces such as tunnels. This study applied the computational fluid dynamics (CFD) simulations in conjunction with probabilistic calculation methods to determine the associated thermal risk of a hydrogen jet fire in a tunnel and its dependency on scenarios with different tunnel slopes longitudinal and transverse ventilation velocities and fire positions. A large-scale model of 102 m in which the effects of outlined parameter variations on the severity of the fire incident were analysed. It is found that both tunnel ventilation techniques and slope were critical for the effective ejection of accumulated heat. With ventilation playing a primary role in the ejection of heat and gas and slope ensuring the stability of the ejected heat probabilities of thermal burns were found to be reduced by up to approximately 35% with a strong suggestion of critical combinations to further reduce the dangers of hydrogen tunnel fires.
Analysis of a Large Balloon Explosion Incident
Sep 2021
Publication
On December 19 2017 a large balloon containing about 22 thousand cubic meters of hydrogen was deliberately torn open to initiate deflation at the completion of a filling test. An inadvertent ignition occurred after about two seconds and caused an explosion that produced extensive light damage to a large building near the balloon test pad. The analysis described here includes an estimate of the buoyancy induced mixing into the torn balloon and the blast wave produced by assumed constant flame speed combustion of the 55% to 65% hydrogen-in-air mixture. Comparisons of calculated blast wave pressures are consistent with estimates of the pressure needed to cause the observed building damage for flame speeds in the range 85 m/s to about 100 m/s.
No more items...