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Field Test Series for Development of Mitigation Barriers and its Designs Against Hydrogen Explosion
Sep 2023
Publication
A field test series where a composite pressure vessel for hydrogen is exploded by fire 1) to provide the facts and the data for the safety distance based on overpressure; 2) to validate the current status of mitigation barrier per KGS FP216 and further designs for developments of the codes and standards relating to hydrogen refueling stations. A pair of barriers to be tested are installed approximately 4 m apart standing face to face. The explosion source is a type-4 composite vessel of 175 L filled with compressed hydrogen up to 70 MPa. The vessel is in the middle of the barriers and the body part is heated with an LPG burner until it blows out. The incident overpressures from the blast are measured with 40 high-speed pressure sensors which are respectively installed 2 to 32 m away from the explosion. In the tests with the barrier constructed per the current status of KGS FP216 the explosion of the vessel resulted in partial destruction of the reinforced concrete barrier and made the steel plate barrier dissociated from the foundation then flew away approximately 25 m. The peak overpressure was 14.65 kPa at 32 m. The test data will be further analyzed to select the barriers for the subsequent tests and to develop the codes and standards for hydrogen refueling stations.
Enhancing Safety of Liquid and Vaporised Hydrogen Transfer Technologies in Public Areas for Mobile Applications
Sep 2023
Publication
Federico Ustolin,
Donatella Cirrone,
Vladimir V. Molkov,
Dmitry Makarov,
Alexandros G. Venetsanos,
Stella G. Giannissi,
Giordano Emrys Scarponi,
Alessandro Tugnoli,
Ernesto Salzano,
Valerio Cozzani,
Daniela Lindner,
Birgit Gobereit,
Bernhard Linseisen,
Stuart J. Hawksworth,
Thomas Jordan,
Mike Kuznetsov,
Simon Jallais and
Olga Aneziris
International standards related to cryogenic hydrogen transferring technologies for mobile applications (filling of trucks ships stationary tanks) are missing and there is lack of experience. The European project ELVHYS (Enhancing safety of liquid and vaporized hydrogen transfer technologies in public areas for mobile applications) aims to provide indications on inherently safer and efficient cryogenic hydrogen technologies and protocols in mobile applications by proposing innovative safety strategies which are the results of a detailed risk analysis. This is carried out by applying an inter-disciplinary approach to study both the cryogenic hydrogen transferring procedures and the phenomena that may arise from the loss of containment of a piece of equipment containing hydrogen. ELVHYS will provide critical inputs for the development of international standards by creating inherently safer and optimized procedures and guidelines for cryogenic hydrogen transferring technologies thus increasing their safety level and efficiency. The aim of this paper is twofold: present the state of the art of liquid hydrogen transfer technologies by focusing on previous research projects such as PRESLHY and introduce the objectives and methods planned in the new EU project ELVHYS.
A Model for Assessing the Risk of Liquid Hydrogen Transport through Road Tunnels
Sep 2023
Publication
Among the new energy carriers aimed at reducing greenhouse gas emissions the use of hydrogen is expected to grow significantly in various applications and sectors (i.e. industrial commercial transportation etc.) due to its high energy content by weight and zero carbon emissions. The increasingly widespread use of hydrogen will require massive distribution from production sites to final consumers and the delivery by means of liquid hydrogen road tankers may be a suitable cost-effective option for market penetration in the short-medium term. Liquid hydrogen (LH2) presents different hazards compared to gaseous hydrogen and an accidental release in confined spaces such as road tunnels might lead to the formation of a flammable hydrogen cloud that might deflagrate or even detonate. Nevertheless the potential negative effects on users in the event of accidental leakage of liquid hydrogen from a tanker in road tunnels so far have not been sufficiently investigated. Therefore a 3D Computational Fluid Dynamics model for the release of LH2 and its dispersion within a road tunnel was developed in this study. The proposed model was validated by a comparison with certain experimental and numerical studies found in the literature. Such modeling is demanding for long tunnels. Therefore the results of the simulations (e.g. the amount of hydrogen contained within the cloud) were combined with established simplified consequence methods to estimate the overpressures generated from a potential hydrogen deflagration. This was then used to evaluate the effects on users while evacuating from the tunnel. The findings showed that the worst scenario is when the release is in the middle of the tunnel length and the ignition occurs 90 s after the leakage.
Safety Challenges Related to the Use of Hydrogen-Natural Gas Blends in Gas Turbines
Sep 2023
Publication
In a context of the decarbonization of the power sector the gas turbine manufacturers are expected tohandle and burn hydrogen or hydrogen/natural gas mixtures. This evolution is conceptually simple in order to displace CO2 emissions by H2O in the combustion exhaust but raises potential engineering andsafety related questions. Concerning the safety aspect the flammability domain is wider and the laminar flame speed is higher for hydrogen than for natural gas. As a result handling fuels with increased hydrogen concentration should a priori lead to an increased the risk of flammable cloud formation with air and also increase the potential explosion violence.<br/>A central topic for the gas turbine manufacturer is the quantification of the hydrogen fuel content from which the explosion risk increases significantly when compared with the use of natural gas. This work will be focused on a risk study of the fuel supply piping of a gas turbine in a scenario where mixing between fuel and air would occur. The pipes are a few dozens of meters long and show singularities: elbows connections with other lines … They are operated at high temperature and atmospheric or high pressure.<br/>The paper will first highlight through CFD modelling the impact of increasing hydrogen content in the fuel on the explosion risk based on a geometry representative of a realistic system. Second the quantification of the explosion effects will be addressed. Some elements of the bibliography relative to flame propagation in pipes will be recalled and put in sight of the characteristics of the industrial case. Finally a CFD model proposed recently for accounting for methane or hydrogen flames propagating in long open steel tubes was used to assess a hydrogen fuel content from which the flame can strongly accelerate and generate significative pressure effects for a flammable mixture initially at atmospheric conditions.
CFD Modelling of Startup Fuelling Phase Accounting for All Hydrogen Refuelling Station Components
Sep 2023
Publication
Further development of hydrogen-fuelled transport and associated infrastructure requires fundamentally based validated and publicly accepted models for fuelling protocol development particularly for heavy-duty transport applications where protocols are not available yet. This study aims to use computational fluid dynamics (CFD) for modelling the entire hydrogen refuelling station (HRS) including all its components starting from high-pressure (HP) tanks a mass flow meter pressure control valve (PCV) a heat exchanger (HE) nozzle hose breakaway and up to 3 separate onboard tanks. The paper focuses on the initial phase of the refuelling procedure in which the main purpose is to check for leaks in the fuelling line and determine if it is safe to start fuelling. The simulation results are validated against the only publicly available data on hydrogen fuelling by Kuroki and co-authors (2021) from the NREL hydrogen fuelling station experiment. The simulation results – mass flow rate dynamics as well as pressure and temperature at different station locations - show good agreement with the measured experimental data. The development of such models is crucial for the further advancement of hydrogen-fuelled transport and infrastructure and this study presents a step towards this goal.
Improvement of MC Method in SAE J2601 Hydrogen Refuelling Protocol Using Dual-zone Dual-Temperature Model
Sep 2023
Publication
The MC method refuelling protocol in SAE J2601 has been published by the Society of Automotive Engineers (SAE) in order to safely and quickly refuel hydrogen vehicles. For the calculation method of the pressure target to control the refuelling stop we introduced a dual-zone dual-temperature model that distinguishes the hydrogen temperature in the tank from the wall temperature to replace the dual-zone single-temperature model of the original MC method. The total amount of heat transferred by convection between hydrogen and the inner tank wall during the filling process was expressed as an equation of final hydrogen temperature final wall temperature final refuelling time tank inner surface area and the correction factor. The correction factor equations were determined by fitting simulation data from the 0D1D model where hydrogen inside the tank is lumped parameter model (0D) and the tank wall is a one-dimensional model (1D). For the correction factor of the linear equation its first-order coefficient and constant term have a linear relationship with the initial pressure of the storage tank and their R2 values obtained from the fitting are greater than 0.99. Finally we derived a new equation to calculate the final hydrogen temperature which can be combined with the 100% SOC inside the vehicle tank to determine the pressure target. The simulation results show that the final SOC obtained are all greater than 96% using the modified pressure target and the correction factor of the linear equation.
Risk Management in a Containerized Metal Hydride Storage System
Sep 2023
Publication
HyCARE project supported by the Clean Hydrogen Partnership of the European Union deals with a prototype of hydrogen storage tank using a solid-state hydrogen carrier. Up to 40 kilograms of hydrogen are stored in twelve tanks at less than 50 barg and less than 100 °C. The innovative design is based on a standard twenty-foot container including twelve TiFe-based metal hydride (MH) hydrogen storage tanks coupled with a thermal energy storage in phase change materials (PCM). This article aims at showing the main risks related to hydrogen storage in a MH system and the safety barriers considered based on HyCARE’s specific risk analysis.<br/>Regarding the TiFe MH material used to store hydrogen experimental tests showed that the exposure of the MH to air or water did not cause spontaneous ignition. Furthermore an explosion within the solid MH cannot propagate due to internal pore size. Additionally in case of leakage the speed of hydrogen desorption from the MH is self-limited which is an important safety characteristic since it reduces the potential consequences from the hydrogen release scenario.<br/>Regarding the integrated system the critical scenarios identified during the risk analysis were: explosion due to release of hydrogen inside or outside the container internal explosion inside MH tanks due to accidental mix of hydrogen and air and asphyxiation due to inert gas accumulation in the container. This identification phase of the risk analysis allowed to pinpoint the most relevant safety barriers already in place and recommend additional ones if needed to further reduce the risk that were later implemented.<br/>The main safety barriers identified were: material and component selection (including the MH selected) safety interlocks safety valves ventilation gas detection and safety distances.<br/>The risk management process based on risk identification and assessment contributed to coherently integrate inherently safe design features and safety barriers.
Study on the Inherent Safety of On-board Methanol Reforming Hydrogen Production Fuel Cell System
Sep 2023
Publication
Methanol as a liquid phase hydrogen storage carrier has broad prospects. Although the on-board methanol reforming hydrogen fuel cell system (MRFC) has long been proposed to replace the traditional hydrogen fuel cell vehicle the inherent safety of the system itself has rarely been studied. This paper adopted the improved method of Inherently Safer Process Piping (ISPP) to evaluate the pipeline inherent safety of MRFC. The process data such as temperature pressure viscosity and density were obtained by simulating the MRFC in ASPEN HYSYS. The Process Stream Characteristic Index (PSCI) and risk assessment of jet fire and vapor cloud explosion was carried out for the key streams with those simulated data. The results showed the risk ranks of different pipelines in the MRFC and the countermeasures were given according to different risk ranks. Through the in-depth study of the evaluation results this paper demonstrates the risk degree of the system in more detail and reduces the fuzziness of risk rating. By applying ISPP to the small integrated system of MRFC this paper realizes the leap of inherent safety assessment method in the object and provides a reference for the inherent safety assessment of relevant objects in the future.
Engineering Models for Refueling Protocol Development: Validation and Recommendations
Sep 2023
Publication
Fouad Ammouri,
Nicola Benvenuti,
Elena Vyazmina,
Vincent Ren,
Guillaume Lodier,
Quentin Nouvelot,
Thomas Guewouo,
Dorine Crouslé,
Rony Tawk,
Nicholas Hart,
Steve Mathison,
Taichi Kuroki,
Spencer Quong,
Antonio Ruiz,
Alexander Grab,
Alexander Kvasnicka,
Benoit Poulet,
Christopher Kutz and
Martin Zerta
The PRHYDE project (PRotocol for heavy duty HYDrogEn refueling) funded by the Clean Hydrogen partnership aims at developing recommendations for heavy-duty refueling protocols used for future standardization activities for trucks and other heavy duty transport systems applying hydrogen technologies. Development of a protocol requires a validated approach. Due to the limited time and budget the experimental data cannot cover the whole possible ranges of protocol parameters such as initial vehicle pressure and temperature ambient and precooling temperatures pressure ramp refueling time hardware specifications etc. Hence a validated numerical tool is essential for a safe and efficient protocol development. For this purpose engineering tools are used. They give good results in a very reasonable computation time of several seconds or minutes. These tools provide the heat parameters estimation in the gas (volume average temperature) and 1D temperature distribution in the tank wall. The following models were used SOFIL (Air Liquide tool) HyFill (by ENGIE) and H2Fills (open access code by NREL). The comparison of modelling results and experimental data demonstrated a good capability of codes to predict the evolution of average gas temperature in function of time. Some recommendations on model validation for the future protocol development are given.
An Improved Passive Scalar Model for Hazardous H2-Air Ignition Prediction
Sep 2023
Publication
As hydrogen becomes an increasingly popular alternative fuel for transportation the need for tools to predict ignition events has grown. Recently a cost-effective passive scalar formulation has been developed to address this need [1]. This approach employs a self-reacting scalar to model the hydrogenair chain-branched explosion (due to reactions of the type Reactant + Radical → Radical + Radical). The scalar branching rate is derived analytically from the kinetic Jacobian matrix [2]. The method accurately reproduces ignition delays obtained by detailed chemistry for temperatures above crossover where branching is the dominant process. However for temperatures below the crossover temperature where other phenomena like thermal runaway are more significant the scalar approach fails to predict ignition events correctly. Therefore modifications to the scalar framework have been made to extend its validity across the entire temperature range. Additionally a simple technique for approximating the molecular diffusion of the scalar has been developed using the eigenvector of the Jacobian which accounts for differences in the radical pool’s composition and non-unity Lewis number effects. The complete modified framework is presented and its capability is evaluated in canonical scenarios and a more challenging double mixing layer.
Calculating the Fundamental Parameters to Assess the Explosion Risk Due to Crossover in Electrolysers
Sep 2023
Publication
With the predicted high demand of hydrogen projected to support the neutral carbon society transition in the coming years the production of hydrogen is set to increase alongside the demand. As electrolysis is set to be amongst the main solutions for green hydrogen production ensuring the safety of electrolysers during operation will become a central concern. This is mainly due to the crossover risk (hydrogen into oxygen or the other way around) in the separators as throughout the years several cases of incidents have been reported. This study aims to evaluate the methodologies for calculating H2/O2 detonation cell size and laminar flame velocity using detailed kinetic mechanisms at the operating conditions of electrolysers (up to 35 bar and 360 K). Therefore the modeling of H2/O2 and H2/Air shock tube delay times and laminar flame speeds at initial different pressures and temperature based on the GRI mech 3.0 [1] Mevel et al.[2] Li et al.[3] Lutz et al. [4] and Burke et al. [5] kinetic mechanisms were performed and compared with the available experimental data in the literature. In each case a best candidate mechanism was then chosen to build a database for the detonation cell size then for the laminar flame speeds up to the operating conditions of electrolysers (293-360K and 1-35 bar).
Impact on Canadian Residential End Use Appliances with the Introduction of Hydrogen into the Natural Gas Stream - An Application
Sep 2023
Publication
Canada’s commitment to be net-zero by 2050 combined with ATCO’s own Environmental Social and Governance goals has led ATCO to pursue hydrogen blending within the existing natural gas system to reduce CO2 emissions while continuing to provide safe reliable energy service to customers. Utilization of hydrogen in the distribution system is the least-cost alternative for decarbonizing the heating loads in jurisdictions like Alberta where harsh winter climates are encountered and low-carbon hydrogen production can be abundant. ATCO’s own Fort Saskatchewan Hydrogen Blending Project began blending 5% hydrogen by volume to over 2100 customers in the Fall of 2022 and plans to increase the blend rates to 20% hydrogen in 2023. Prior to blending ATCO worked together with DNV to examine the impact of hydrogen blended natural gas to twelve Canadian appliances: range/stove oven garage heater high and medium efficiency furnaces conventional and on demand hot water heaters barbeque clothes dryer radiant heater and two gas fireplaces. The tests were performed not only within the planned blend rates of 0-20% hydrogen but also to higher percentages to determine how much hydrogen can be blended into a system before appliance retrofits would be required. The testing was designed to get insights on safety-related combustion issues such as flash-back burner overheating flame detection and other performance parameters such as emissions and burner power. The experimental results indicate that the radiant heater is the most sensitive appliance for flashback observed at 30 vol% hydrogen in natural gas. At 50% hydrogen the range and the radiant burner of the barbeque tested were found to be sensitive to flashback. All other 9 appliances were found to be robust for flashback with no other short-term issues observed. This paper will detail the findings of ATCO and DNV’s appliance testing program including results on failure mechanisms and sensitivities for each appliance.
Explosion Replication Test of FCEV Hydrogen Tank
Sep 2023
Publication
Due to the increased interest in alternative energy sources hydrogen device safety has become paramount. In this study we induced the explosion of a hydrogen tank from a fuel cell electric vehicle (FCEV) by igniting a fire beneath it and disabling the built-in temperature pressure relief device. Three Type 4 tanks were injected gaseous hydrogen at pressures of 700 350 and 10 bar respectively. The incident pressure generated by the tank explosion was measured by pressure transducers positioned at various points around the tank. A protective barrier was installed to examine its effect on the resulting damage and the reflected pressure was measured along the barrier. The internal pressure and external temperature of the tanks were measured in multiple locations. The 700- and 350-bar hydrogen tanks exploded approximately 10 and 16 min after burner ignition respectively. The 10-bar hydrogen tank did not explode but ruptured approximately 29 min after burner ignition The explosions generated blast waves fireballs and fragments. The impact on the surrounding area was evaluated and we verified that the blast pressure fireballs and fragments were almost completely blocked by the protective barrier. The results of this study are expected to improve safety on an FCEV accident scene.
Experimental Characterization of the Operational Behavior of a Catalytic Recombiner for Hydrogen Mitigation
Sep 2023
Publication
One of the significant safety concerns in large-scale storage and transportation of liquefied (cryogenic) hydrogen (LH2) is the formation of flammable hydrogen/air mixtures after leakages during storage or transportation. Especially in maritime transportation hydrogen accumulations could occur within large and congested geometries. The installation of passive auto-catalytic recombiners (PARs) is a suitable mitigation measure for local areas where venting is insufficient or even impossible. Numerical models describing the operational behavior of PARs are required to allow for optimizing the location and assessing the efficiency of the mitigation measure. In the present study the operational behavior of a PAR with a compact design has been experimentally investigated. In order to obtain data for model validation an experimental program has been performed in the REKO-4 facility a 5.5 m³ vessel. The test procedure includes two phases steady-state and dynamic. The results provide insights into the hydrogen recombination rates and catalyst temperatures under different boundary conditions.
UK HSE Hydrogen for Heating Evidence Review Process
Sep 2023
Publication
As part of the UK Government’s Net Zero targets to tackle Climate Change the Health and Safety Executive (HSE) aims to reach an authoritative view on the safety of using 100% hydrogen for heating across the UK to feed into Government policy decisions by the mid-2020s. This paper describes the background and process of a programme of work led by HSE in support of the Department for Energy Security and Net Zero (formerly BEIS) that will inform strategic policy decisions by 2026. The strategic framework of HSE’s programme of work was defined between BEIS and HSE. HSE’s programme of work follows on from a previous project which engaged with HSE policy regulatory and scientific colleagues working with industry stakeholders identifying knowledge gaps for the safe distribution storage and use of hydrogen gas in domestic industrial and commercial premises. These knowledge gaps were subsequently used in discussions with stakeholders to prioritise research projects and evidence gathering exercises. To review this scientific evidence HSE developed a review framework and convened Evidence Review Groups (ERGs) to cover all evidence areas encompassing topics such as quantified risk assessment material compatibility and operational procedures. These ERGs include representation from relevant divisions across HSE (policy regulation and science). The paper explains the structure of HSE’s input into the hydrogen for heating programme the ERG process and timelines along with the proposed outputs. Additional activities have been undertaken by HSE within the programme to highlight specific issues in support of the review process which will also be discussed.
Computational Fluid Dynamic (CFD) Analysis of a Cold-adsorbed Hydrogen Tank During Refilling
Sep 2023
Publication
Hydrogen has the potential to be an important source of clean energy but the development of efficient and cost-effective methods for storing hydrogen is a key challenge that needs to be addressed in order to make widespread use of hydrogen as a possible energy sourc. There are different methods for storing hydrogen (i.e. compressed it at high pressures liquefied by cooling the hydrogen to a temperature of -253°C and stored with a chemical compound) each with its own advantages and disadvantages.<br/>MAST3RBoost (Maturing the Production Standards of Ultraporous Structures for High Density Hydrogen Storage Bank Operating on Swinging Temperatures and Low Compression) is a European project which aims to provide a solid benchmark of cold-adsorbed H2 storage (CAH2) at low compression (100 bar or below) by maturation of a new generation of ultraporous materials for mobility applications i.e. H2-powered vehicles including road and railway air-borne and waterborne transportation. Based on a new generation of Machine Learning-improved ultraporous materials – such as Activated Carbons (ACs) and high-density MOFs (Metal-organic Frameworks) – MAST3RBoost project will enable a disruptive path to meet the industry goals by developing the first worldwide adsorption-based demonstrator at the kg-scale.<br/>The design of the tank is supported by numerical investigation by mean of the use of Computational Fluid Dynamic (CFD) commercial code. In this a paper a preliminary analysis of the refilling of tank is presented focused on the effect of different tank configurations on the hydrogen temperature and on the hydrogen adsorption.
Safety Aspects Related to the Underground Hydrogen Storage
Sep 2023
Publication
The transition from fossil fuels to the renewable energies (wind solar) is a key factor to face climate change and build a sustainable reliable and secure energy system. To balance the intermittent energy demand and supply affecting the renewable sources the surplus of electrical energy may be converted in hydrogen and then storage in geological formations. While the risks associated to the natural gas storage in the sub-surface are well known from decades those associated with hydrogen underground storage (UHS) are relatively underexplored. This paper presents an inventory of risks related to large H2-storage in depleted gas and oil fields salt caverns and aquifers. Different issues such as integrity and durability of materials H2 leakages and interaction with the reservoir H2 uncontrolled outflow from the wellhead with potential combustion of air-hydrogen mixture (fire and explosion) soil subsidence and induced seismicity are analyzed.
Numerical Simulations of the Critical Diameter and Flame Stability for the Hydrogen Jet Flames
Sep 2023
Publication
This study focuses on development of a CFD model able to simulate the experimentally observed critical nozzle diameter for hydrogen non-premixed flames. The critical diameter represents the minimum nozzle size through which a free jet flame will remain stable at all driving pressures. Hydrogen non-premixed flames will not blow-out at diameters equal to or greater than the critical diameter. Accurate simulation of this parameter is important for assessment of thermally activated pressure relief device (TPRD) performance during hydrogen blowdown from a storage tank. At TPRD diameters below the critical value there is potential for a hydrogen jet flame to blow-out as the storage tank vents potentially leading to hydrogen accumulation in an indoor release scenario. Previous experimental studies have indicated that the critical diameter for hydrogen is approximately 1 mm. In this study flame stability is considered across a range of diameters and overpressures from 0.1 mm to 2 mm and from 0.2 MPa to 20 MPa respectively. The impact of turbulent Schmidt number Sct which is the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity on the hydrogen concentration profile in the region near the nozzle exit and subsequent influence on critical diameter was investigated and discussed. For lower Sct values the enhanced mass mixing resulted in smaller predicted critical diameters. The use of value Sct=0.61 in the model demonstrated the best agreement with experimental values of the critical diameter. The model reproduced the critical diameter of 1 mm and then was applied to predict flame stability for under-expanded hydrogen jets.
CO2 Effect on the Fatigue Crack Growth of X80 Pipeline Steel in Hydrogen-Enriched Natural Gas: Experiment vs Density Functional Theory Calculation
Sep 2023
Publication
The influence of hydrogen-enriched natural gas (HENG) and CO2 on the mechanical property of X80 pipeline steel were investigated via fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The results show that the FCGR in H2 was slightly faster than that in HENG while it was slower than that in the N2/CO2/H2 mixtures. The enhanced FCGR by CO2 further increased with the increasing CO2 content. DFT calculation results show that the adsorbed CO2 on the iron surface significantly increased the migration rate of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel.
Ignition and Flow Stopping Considerations for the Transmission of Hydrogen in the Existing Natural Gas Network
Sep 2023
Publication
This work formed part of the H21 programme whose objective is to reach the point whereby it is feasible to convert the existing natural gas (NG) distribution network to 100% hydrogen (H2) and provide a contribution to decarbonising the UK’s heat and power sectors with the focus on decarbonised fuel at point of use. Hydrogen has an ATEX Gas Group of IIC compared to IIA for natural gas which means further precautions are necessary to prevent the ignition of hydrogen during network operations. Both electrostatic and friction ignition risks were considered. Network operations considered include electrostatic precautions for polyethylene (PE) pipe and cutting and drilling of metallic pipes. As a result of the updated basis of safety from ignition considerations existing flow stopping methods were reviewed to see if they were compatible. Commonly used flow stopping methods were tested under laboratory conditions with hydrogen following the methodologies specified in the Gas Industry Standards (GIS). A new basis of safety for flow stopping has been proposed that looks at the flow past the secondary stop as double isolations are recommended for use with hydrogen.
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