Safety

Currently local regulations governing hydrogen installations vary by geographical region and by country leading to discrepancies in safety and separation distance requirements for similar hydrogen systems. This work carried out in the frame of IEA TCP H2 Task 43 (IEA TCP H2 2022) aims to provide an overview of various methodologies and recommendations established for risk management and consequence assessment in the event of accidental scenarios. It focuses on a case study involving industrial electrolyzers utilizing alkaline and PEM technologies. The research incorporates lessons learned from past incidents offers recommendations for mitigation measures reviews existing methodologies and highlights areas of divergence. Additionally it proposes strategies for harmonization. The study also emphasizes the most significant scenarios and the corresponding leakage sizes

The global shift towards cleaner energy sources is driving the adoption of hydrogen as an environmentally friendly alternative to fossil fuels. Among the forms currently available Liquid Hydrogen (LH2) offers high energy density and efficient storage making it suitable for large-scale transport by rail. However the flammability of hydrogen poses serious safety concerns especially when transported through confined spaces such as railway tunnels. In case of an accidental LH2 release from a freight train the rapid accumulation and potential ignition of hydrogen could cause catastrophic consequences especially if freight and passenger trains are present simultaneously in the same tunnel tube. In this study a three-dimensional computational fluid dynamics model was developed to simulate the dispersion and explosion of LH2 following an accidental leak from a freight train’s cryo-container in a single-tube double-track railway tunnel when a passenger train queues behind it on the same track. The overpressure results were analyzed using probit functions to estimate the fatality probabilities for the passenger train’s occupants. The analysis suggests that a significant number of fatalities could be expected among the passengers. However shorter users’ evacuation times from the passenger train’s wagons and/or longer distances between the two types of trains might reduce the number of potential fatalities. The findings by providing additional insight into the risks associated with LH2 transport in railway tunnels indicate the need for risk mitigation measures and/or traffic management strategies.

Hydrogen (H2) is emerging as a key alternative to fossil fuels in the global energy transition. This study presents a comparative techno-economic analysis of H2 and natural gas (NG) focusing on safety hazards energy output CO2 emissions and cost-effectiveness aspects. Our analysis showed that compared to NG and other highly flammable gases like acetylene (C2 H2) and propane (C3 H8) H2 has a higher hazard potential due to factors such as its wide flammability range low ignition energy and high flame speed. In terms of energy output 1 kg of NG produces 48.60 MJ while conversion to liquefied natural gas (LNG) grey H2 and blue H2 reduces energy output to 45.96 MJ 35.45 MJ and 31.21 MJ respectively. Similarly while unconverted NG emits 2.72 kg of CO2 per kg emissions increase to 3.12 kg for LNG and 3.32 kg for grey H2. However blue H2 significantly reduces CO2 emissions to 1.05 kg per kg due to carbon capture and storage. From an economic perspective producing 1 kg of NG yields a profit of $0.011. Converting NG to grey H2 is most profitable yielding a net profit of $0.609 per kg of NG while blue H2 despite higher production costs remains viable with a profit of $0.390 per kg of NG. LNG conversion also shows profitability with $0.061 per kg of NG. This analysis highlights the trade-offs between energy efficiency environmental impact and economic viability providing valuable insights for stakeholders formulating hydrogen and LNG implementation strategies.

The safe removal transportation and long-term storage of fuel debris in the decommissioning of Fukushima Daiichi is the biggest challenge facing Japan. In the nuclear power field passive autocatalytic recombiners (PARs) have become established as a technology to prevent hydrogen explosions inside the containment vessel. To utilize PAR as a measure to reduce the concentration of hydrogen generated in the fuel debris storage canister which is currently an issue it is required to perform in a sealed environment with high doses of radiation low temperature and high humidity and there are many challenges different from conventional PAR. A honeycombshaped catalyst based on automotive catalyst technology has been newly designed as a PAR and research has been conducted to solve unique problems such as high dose radiation low temperature high humidity coexistence of hydrogen and low oxygen and catalyst poisons. This paper summarizes the challenges of hydrogen generation in a sealed container the results of research and a guide to how to use the PAR for fuel debris storage canisters.

Hydrogen is widely regarded as a promising carbon-free alternative fuel. However the development of low-emission marine gas turbine combustion systems has been hindered by the associated risks of combustion instability also termed as thermoacoustic oscillations. Although there is sufficient literature on hydrogen fuel and combustion instability systematic reviews addressing the manifestations and mechanisms of these instabilities remain limited. The present study aims to provide a comprehensive review of combustion instabilities in hydrogen-enriched marine gas turbines with a particular focus on elucidating the characteristics and underlying mechanisms. The review begins with a concise overview of recent progress in understanding the fundamental combustion properties of hydrogen and then details various instability phenomena in hydrogen-enriched methane flames. The mechanisms by which hydrogen enrichment affects combustion instabilities are extensively discussed particularly in relation to the feedback loop in thermoacoustic combustion systems. The paper concludes with a summary of the key combustion instability challenges associated with hydrogen addition to methane flames and offers prospects for future research. In summary the review highlights the interaction between hydrogenenriched methane flames and thermoacoustic phenomena providing a foundation for the development of stable low-emission combustion systems in industrial marine applications incorporating hydrogen enrichment.

This programme of work aims to generate empirical evidence of gas concentration with respect to distance from the vent tip for a range of hydrogen releases. The measured data is to be compared to the Zone 2 exclusion distances specified by the IGEM/SR/25 hydrogen supplement.

Test cases have been shared with Steer Energy that calculate the new hazardous areas as per the hydrogen supplement for common infrastructure such as pressure regulating installations/stations. The result of these test cases was a significant increase in the calculated hazardous zone distances for hydrogen compared to those for Natural Gas. The overall programme aims are to measure gas releases replicating these test cases and to compare the measured hazardous zones to the calculated hazardous zones. This report covers Stage 1 of the programme of work which comprised an initial examination using small releases as a fast and economical method to assess the likelihood of differences between measured and calculated zones.

Experimental equipment was setup to release gas at controlled flow rates to match those of the IGEM/SR/25 hydrogen supplement tables. A moveable array of gas detectors was positioned above the vent tip to measure the shape and magnitude of the resulting gas plume from the release.

In all 22 tests were conducted with gas released from two different vent diameters 13 mm and 48 mm. Two gas types hydrogen and methane were used. Ideal and non-ideal vents were tested across a limited range of flows. The measured data enabled colourmaps of the vents to be created showing the shape and magnitude of the resulting gas plumes.

The results of the study have shown that in all cases the shape of the plumes from the measured vents are significantly different to the dispersion distances specified in the relevant tables of IGEM/SR/25. In most cases no gas was detected throughout the majority of the specified hazardous area instead a thin vertical cylindrical plume of gas was measured often extending above the specified dispersion zones. This was seen in both hydrogen and methane tests.

The test results from this initial phase of the project cast some doubt on the findings from the previous NIA project ATEX Equipment & SR/25 Modification Assessment that used the SR/25 calculator developed from the hydrogen supplement tables. In some instances the horizontal dispersion distance for hydrogen was calculated to be over 6 times the value for Natural Gas (see Figure 2) with its resulting hazardous area exclusion zone having potentially serious consequences on the viability of the corresponding AGIs without mitigations. However results from the initial tests undertaken during this phase of work demonstrate significant inconsistencies between the calculated results and empirical tests. This should be further investigated in phase 2 as initial conclusions show that the larger hazardous zones mentioned above are seemingly overstating the risk. The previous work also modelled the hazardous areas using full bore releases whereas relief valves on the network tend to incorporate flow limiting orifices therefore further exacerbating the perceived increased risk.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

This project has built on the Hazardous Area Impact Mitigation (HAIM) Phase 1 project (NIA2_SGN0041) results that identified a disparity between hazardous zones measured during initial testing and those specified in the IGEM/SR/25 Hydrogen supplement. The aim of the HAIM Phase 2 project is to scale up the measurements to confirm the behaviour of larger vents equivalent to the test cases presented in the ATEX Equipment & IGEM/SR/25 Modification Assessment (NGNG_NIA_346) project.

The formation of a technical review group has informed the project team of the parameters and some of the assumptions used for the modelling leading to the development of the SR/25 Hydrogen Supplement. The difference between the modelled and measured data seen in the HAIM Phase 1 project has been attributed to the modelled data being carried out under a minimum of 0.5 m/s cross winds. Completely still conditions are not expected to occur hence this 0.5 m/s minimum. The result of this wind on the model leads to a significant reduction of the height of the resulting plume and a corresponding increase in the radial displacement of the plume from the vent tip. This has shifted the focus of this project towards examining wind influenced vents.

Two sets of experiments are provided in this interim report: measurements of plumes from wind influenced vents and plumes from fixtures and fitting leaks. The report also includes early results from plume ignition studies which have shown that ignition is not instantaneous for high velocity plumes.

The wind influenced plume tests have measured 0.0005 kg/s hydrogen releases from 50 mm and 15 mm vent pipes. The largest hazardous zone for these releases stipulated in IGEM/SR/25 hydrogen supplement is Xr = 2.5 m and Xh = 1.5 m so these were used as the extent of measurement. With no wind the plume rises vertically from the vent tip with no radial deflection. Measured concentration peaks have exceeded the lower flammable limit (LFL) at the 1.5 m measurement height. The influence of wind radially displaces the plume the higher the wind the larger the displacement. Concentration peaks are reduced but a wind of 0.5 m/s still permitted levels above the 4 % LFL value. Wind levels of 1.0 m/s displaced the plume to the end of the 2.5 m measurement array. Wind levels of 1.5 m/s broke up the plumes potentially driving pockets of gas beyond the 2.5 m measurement array.

Partial ignition of both vent types was possible at 1.5 m above the vent tip but complete sustained ignition was only possible when closer than 1 m to the vent tip.

Plumes from higher pressure (above 0.1 barg) fixture and fitting leaks have shown a good correlation between the shapes of modelled and measured vents. Except for the lowest pressure leaks which are momentum-dominated jets the resulting plumes are long and thin unaffected by buoyancy. The concentration decay in measured plumes is observed to be faster with distance compared to modelled values. Typically the measured distance to reach 2 % volume from the leak position is about half of the specified zone distances.

Limited ignition tests have been conducted but ignition from a 2 barg adverse downward pointing leak was challenging beyond 30 cm from the leak. The hydrogen jet also repeatably extinguished the methane flame used as pilot light during tests.

The next steps for the project are to carry out more measurements and to scale up the magnitude of the gas releases. This will provide more evidence supporting specified magnitudes of hazardous zones. In addition it is proposed that mitigation measures are explored that could reduce the specified hazardous zones for given vents. This could include design guidelines for hydrogen vents.

Further ignition tests will also be conducted to assess required conditions such as flow direction and gas concentration required to achieve both partial and stable ignition of hydrogen vents.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

Multiple Occupancy Buildings (MOBs) account for 21% of the UK’s domestic heating demand and tackling the challenge to decarbonise these properties will be key to meeting Government net zero targets.1 There is therefore a requirement for gas distribution network operators (GDNOs) to understand the cost safety and practicality of converting gas supplies to hydrogen. This project aimed to address evidence gaps centred around commissioning and decommissioning of risers associated with MOBs in particular purging operations.

The project has carried out a review of processes procedures and tooling used for purging MOBs examined site surveys and discussed purging with operators. Riser systems in MOBs are branched systems often comprising many vertical and horizontal elements taking a single supply source and distributing it to multiple individual dwellings in the building. Purging this network of elements is caried out in a routine manner as dictated by standards and procedures. Routine purging of MOBs is not challenging and this will continue to be the same when using hydrogen. The greatest challenge identified to purging MOBs is when each individual dwelling needs to be accessed to complete the purge. If an individual dwelling is inaccessible and individual lateral isolation valves are not installed then unpurged branches can remain. A consequence of leaving branches unpurged is a mixing of the air and fuel into a flammable mixture in the riser.

An experimental programme of work has been developed to investigate dispersion in unpurged branches of risers using methane and hydrogen. The experiments started with single pipes and developed in complexity to a branched system with six laterals. The main conclusions are: • If an unpurged branch is left over time the flammable volume at the interface between purged and unpurged sections will increase. Pipe diameter is the dominant parameter that dictates the speed of mixing of the two gases. • Gas dispersion occurs through a combination of buoyancy and diffusion buoyancy effects are diameter dependent becoming more dominant in pipe diameters greater than 50 mm. Below 50 mm gas dispersion is slow being dominated by diffusion alone. • Diffusion driven dispersion acts in the direction of concentration gradient from high to low. This acts to reduce the driving concentration gradient and slows down subsequent diffusion. In vertical pipes concentration gradients have been seen to act upwards or downwards. • Buoyancy effects act preferentially upwards but also promote mixing of different density gases in horizontal pipes. • In tests hydrogen dispersion was up to twice as fast as methane dispersion.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

In line with the UK government’s de-carbonisation strategy Northern Gas Network’s (NGN) H21 project aims to demonstrate the feasibility of converting the existing <7barg gas distribution network to 100% hydrogen. Following progress on Phase 1 of the H21 programme Phase 2 was proposed to build on the knowledge acquired to provide further quantified safety-based evidence on the suitability of the GB networks to transport 100% hydrogen. Phase 2 consisted of a number of Project Phases. Phase 2b evaluates network operational procedures identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve this a gas demonstration network was built at South Bank Middlesbrough TS6 6LF to accommodate full scale network parameters and typical network components. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the HSE and DNV to address various aspects of existing network procedures and operations including:

♦ Emergency Response and bad practice demonstrations

♦ Finding Leaks

♦ Accessing Leaks

♦ Assessment of repair techniques

♦ Planned live gas operations

♦ Isolation techniques

♦ Commissioning and decommissioning activities

♦ Pressure regulation and maintenance procedures

♦ Pressure and flow validation

Each of these areas of testing and assessments were then divided in individual tests or tasks and identified with a unique ID name.

This current report details the work conducted in the NGN H21 testing facility at South Bank in RedCar with the maintenance of a Honeywell MP-LP Twin Stream Governor. The programme included the maintenance functional checks and a major overhaul operation conducted on the twin stream governor. This was completed on the hydrogen network within the facility.

This report details the Honeywell Twin Stream Regulator and the flow demands in section 3. The demonstrations set-up maintenance procedure and method statement used in Section 4; the results and main observations in Section 5 followed by interpretation of results and conclusions in Section 6. Appendix A at the back of the document contains site evidence for the demonstration.

In line with the UK government's de-carbonisation strategy Northern Gas Network's (NGN) H21 project aims to enable the conversion of the UK gas networks to pure hydrogen. After conversion of the gas networks hydrogen is transported from various sources through new and existing gas networks to industrial and domestic customers.

Following progress on Phase 1 of the H21 programme Phase 2 consisted of a number of Project Phases. Phase 2a evaluates network operations tools and procedures identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve this a gas demonstration network was built at DNV Spadeadam Research and Testing to accommodate full scale network parameters and typical network components. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the HSE S&RC and DNV to address various aspects of existing network procedures and operations including:

♦ Emergency Response and bad practice demonstrations

♦ Finding leaks

♦ Accessing leaks

♦ Assessment of repair techniques

♦ Live gas operations

♦ Isolation techniques

♦ Commissioning and decommissioning activities

♦ Pressure regulation and maintenance procedures

♦ Pressure and flow validation

Each of these areas of testing and assessments were then divided in individual tests or tasks and identified with a unique ID name.

The current report details the work conducted in the H21 demonstration grid at Spadeadam herein referred to as ""Microgrid"" in relation to commissioning and decommissioning activities. The programme included commissioning and decommissioning of straight mains branched networks and service pipes in each of the pressure tiers in the microgrid (IP MP and LP). In line with recommendations by the HSE S\&RC in their procedure review conducted earlier in Phase 2a; pipe diameters above 32 mm were commissioned or decommissioned indirectly (by displacing air with inert fluid followed by displacement of the inert fluid with hydrogen or vice versa). Pipe diameters under 32 mm (service pipe tests) were purged directly (air displaced by fuel gas or vice versa) according to a bespoke test procedure employing exclusion zones around pipes and vents.

Conversion style commissioning was also carried out in IP MP and LP mains i.e. converting pipes previously commissioned with Natural Gas to contain 100% hydrogen. This was also carried out by direct displacement of one fuel gas for the other.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.