Hydrogen is expected to play a key role in the decarbonization of the energy system. As of June 2022, more than 30 hydrogen strategies and roadmaps have been published by governments around the world. Hydrogen has been identified as a potential safety issue based on the fact that it is the smallest molecule that exists and can easily pass through materials. To date, however, very little attention has been paid to the potential contribution of hydrogen leakage to climate change, driven by hydrogen’s indirect global warming effect through mechanisms that extend the lifetime of methane and other greenhouse gases (GHG) in the atmosphere (Paulot et al. 2012; Derwent et al. 2020).
A literature analysis turns up very little data on hydrogen leakage along the existing value chain, and that which does exist comes from theoretical assessments, simulation, or extrapolation rather than measures from operations. As the production methods and uses of hydrogen evolve over time, there is even less data available on what could represent key parts of the hydrogen economy going forward. In the future, leaked hydrogen will likely be concentrated in a few key processes (e.g., green hydrogen production, delivery, road transport, and chemical production). There is a risk of increased leakage rates in the future mostly because the leaking processes that will be key by 2050 do not exist at scale today. A high-risk scenario based on hydrogen demand from the International Energy Agency (IEA) net-zero scenario (528 million tons [Mt] by 2050) (IEA 2021) could potentially lead to a 5.6 percent economy-wide leakage rate, compared with an estimated 2.7 percent in 2020.
Using a wide analytical lens encompassing hydrogen leakage detection, prevention, and regulation, this commentary identifies the following three main requirements for mitigating this risk:
- Gathering and analysis of data, especially cross-referenced data from actual measures, to better understand current and future hydrogen leakage rates.
- Research and development to improve hydrogen leakage detection, prevention, and mitigation. Hydrogen sensors must be able to detect leakage at much lower detection thresholds than those existing and among various types of applications. Such technologies are available but need to be transferred and developed at scale.
- Regulations that look beyond safety concerns related to hydrogen’s flammability to include the use of hydrogen in different parts of the energy system and tackle leakage of substances more broadly, including hydrogen. It is important that the regulating entities involved coordinate at national and international levels to achieve coherent regulations.
Hydrogen Use and Related Climate Risk
Hydrogen is emerging as a central pillar of the transition to a net-zero emissions energy system to address the climate crisis. Today, hydrogen is used at scale in several key industrial processes, namely, chemicals, refineries, and iron and steel, totaling around 90 Mt-H2/yr globally (IEA, Net Zero by 2050, 2021). More than 90 percent of the hydrogen produced today is gray hydrogen, meaning it is produced through carbon-intensive methods using fossil fuels. Under the IEA’s net-zero emissions scenario, hydrogen use would more than quintuple by 2050, increasing to 528 Mt-H2/yr (IEA 2021), and come to span a much wider range of applications, including energy storage mediums and fuel for power generation, industrial heat, low-carbon fuel feedstock, natural gas blending, and transportation fuel. In the interim, low-carbon hydrogen production, both green (based on low-carbon electricity electrolysis) and blue (based on reforming fossil fuels with carbon capture and storage), will gradually make up more and more of the total share of hydrogen production. By 2050, it will comprise the overwhelming majority at 520 Mt-H2/yr globally or 97 percent of total supply (see Figure 1).
Most analyses of climate risks related to hydrogen are limited to GHG emissions from various hydrogen production processes—a point highlighted by the attempt to color-code these processes according to their footprint range. However, hydrogen molecules themselves pose a particular climate risk in the atmosphere. Though hydrogen molecules (H2) does not directly trap heat, it has an indirect global warming effect by extending the lifetime of other GHGs. Certain GHGs such as methane, ozone, and water vapor are gradually neutralized by reacting with hydroxide radicals (OH) in the atmosphere. When H2 reaches the atmosphere, however, the H2 molecule reacts with OH instead, depleting atmospheric OH levels and delaying the neutralization of the GHGs, which effectively increases the lifetime of these GHGs (Derwent et al. 2020). Hydrogen molecules last only a few years in the atmosphere, so they exert a substantial near-term warming effect. A recent preprint study modeling continuous emissions of H2 estimated that over a 10-year period hydrogen has an approximately 100 times stronger warming effect than carbon dioxide (CO2) (Ocko and Hamburg 2022). The indirect global warming effect of hydrogen leakage into the atmosphere is rarely considered on a large scale.
Given that the use of hydrogen is projected to expand significantly across various scenarios consistent with reaching net-zero targets, it is important to ensure that it does not contribute to rather than reduce GHG emissions. There is currently very little information on hydrogen leakage risks beyond safety concerns, and only a few independent studies have systematically studied the topic (Frazer-Nash Consultancy 2022).
Figure 1: Sankey diagrams of global hydrogen flow (million metric tons of H2 per year) by process
Hydrogen Leakage: Knowns and Unknowns
Hydrogen leakage risks have been identified along the entire value chain of hydrogen. In assessing these risks, this commentary divides the hydrogen value chain into three categories: production, delivery, and end use (see Figure 1).
Production Leakage Risks
Gray and blue hydrogen production facilities are typically part of integrated industrial facilities where the hydrogen is directly consumed in the production of, for instance, ammonia, methanol, or direct reduced iron (IEA 2021). These industrial facilities have a well-established history of regulating hydrogen safety with a focus on limiting the concentration of flammable gases, including hydrogen, in the air (Rivkin, Burgess, and Buttner 2015). Measurements of leakage rates from industrial gray and blue hydrogen production are rarely implemented and reported. Most of the studies that address gray and blue hydrogen leakage are simulations based on or extrapolated from similar studies of other gases. Xia et al. (2019) found that gray hydrogen production based on steam methane reforming (SMR) could have a less than 1 percent total leakage rate from SMR facilities based on detected nitrogen leakage. Blue hydrogen production is believed to have a slightly higher risk of leakage due to the added complexities of its production system, including an additional separation process. Its leakage rate has been estimated to be approximately 1.5 percent based on a combination of natural gas leakage data and what is known about the correlation between hydrogen leakage properties and those of natural gas (Barrett and Cassarino 2011).
Green hydrogen production currently represents a small share of global hydrogen production, but that share is expected to play a significant role in the future. Assessing the risk of hydrogen leakage during green hydrogen production is difficult as the topic has rarely been studied. The literature on green hydrogen has instead examined hydrogen “losses,” or the difference between the theoretical, calculated quantity of hydrogen that is supposed to be produced and the amount that is actually measured. As part of the University of California–Irvine’s power-to-gas demonstration with a proton exchange membrane (PEM) electrolyzer, one study suggested that the difference between wet and dry hydrogen after the pressure swing adsorption dryer, which comprises two dryer beds that absorb water at elevated pressure, could be caused by the venting of a fixed amount of hydrogen gas (Stansberry 2018, 81). Similarly, a National Renewable Energy Laboratory (NREL) study of a prototype PEM electrolyzer found that most hydrogen losses (estimated at 3.4 percent) occur in the dryer, resulting in a total loss of about 4 percent (Harrison and Peters 2013). If these hydrogen losses are not properly treated, they will eventually leak into the atmosphere.
Delivery Leakage Risks
Compared with the production and end-use phases, the delivery phase of hydrogen (i.e., transport from production site to end user) is the most widely studied, including through both simulation-based and experimental-based research. There are also existing regulations around hydrogen delivery leakage (e.g., Department of Energy [DOE] targets 2022).
Pipelines, including both dedicated hydrogen pipelines and natural gas blending systems, are the most important systems for hydrogen delivery. In and of themselves, these systems demonstrate a low risk of leakage. Weller, Hamburg, and von Fischer (2020) and Mejia and Brouwer (2019) found a roughly 0.4 percent leakage rate for hydrogen simply passing through a pipeline. In the future, however, full hydrogen delivery systems will include necessary storage facilities (e.g., pressurized tank storage, liquefaction tank storage, and salt caverns) that will incur mechanical loss (e.g., from pressurization, depressurization, permeation leakage, and accidents), and the life-cycle loss of hydrogen from integrated transportation/storage systems is estimated to be 2 percent (Panfilov 2015; US DOE 2022).
Another hydrogen delivery method is truck delivery to fueling stations, which are many in number but have a low capacity of only a few hundred to a few thousand tons (Park et al. 2014). Compared with pipeline systems, this method is both less important in terms of scale and leakier, mostly due to boil-off losses (US DOE 2017; Petitpas 2018). For particularly small facilities (<100 kg per day), the loss can contribute to a significant proportion of total accounted hydrogen, estimated to be above 20 percent. Even for average-sized fueling stations (several hundreds to several thousands of kilograms per day), the leakage rate can be 3–6 percent depending on pressure and charging times (US DOE 2017; Petitpas 2018). Given the average size of fueling stations, this study assumes an average leakage rate of 5 percent for truck transport and storage systems.
End-Use Leakage Risks
End-use leakage risks are the least understood of the three categories, especially in terms of future hydrogen end uses that do not exist today. The largest consumers of hydrogen by scale are and will remain within the industrial sector (see Figure 1). Among the current end users of hydrogen, the overwhelming majority are chemical plants, refineries, and iron and steel producers (IEA 2019). In the IEA’s net-zero scenario, these end users are expected to consume around 200 Mt of hydrogen by 2050. Like the case of the chemical industry, current regulations around hydrogen leakage focus on safety measures: how refineries and chemical plants can minimize hydrogen leakage to prevent large-scale hazards (e.g., fires and explosions) as evidenced in quantitative risk analysis studies (Mohammadfam and Zarei 2015; Spouge 2005) and plant surveys (Pattabathula, Rani, and Timbres 2005). The task of quantifying and monitoring small, distributed leaks is not a priority and is therefore largely absent from the literature. To the knowledge of the authors, no explicit leakage rates have been published for industrial facilities, most of which use hydrogen produced on-site as an integrated system. Combining knowledge of integrated systems with that of gray hydrogen production leakage, this analysis assumes a leakage rate of around 0.5 percent for industrial facilities such as chemicals and synthetic fuel, iron and steel, and refineries (excluding the production process).
Other end-use cases include the following:
- Electricity generation: The IEA’s net-zero scenario expects 88 Mt/yr of hydrogen to be used for power generation. Combining Alvarez et al. (2011), which analyzed methane leakage for turbines, with Mejia and Brouwer (2019), which analyzed the correlation between methane and hydrogen leakage, the authors estimate that the process of converting hydrogen to power based on gas-turbine technology has a 3 percent hydrogen leakage rate.
- Transportation: Shen et al. (2021) conducted a simulation study to analyze the effect of the diameter of a storage tank leakage point. Hao et al. (2020) analyzed the leakage leading to hydrogen concentration in a confined space. This study assumes that road transport leakage is similar to hydrogen storage tank leakage during delivery, with the exception of potential boil-off loss during charging, leading to a leakage estimate of 2.3 percent (Alvarez et al. 2011; Mejia and Brouwer 2019). The leakage rates for shipping and aviation have been extrapolated from, in the former case, road transport for similar fuel-cell based technologies (2.3 percent) and, in the latter case, power generation based on turbine-based technologies (3 percent).
- Buildings: Buildings using hydrogen represent a relatively small risk of leakage. Most fuel used by buildings (about 16.2 Mt/yr) is for heating via various kinds of appliances. Borrowing from a study of California’s natural gas emissions from homes and again accounting for methane versus hydrogen leakage correction, this commentary assumes a leakage rate of about 0.8 percent (Fischer et al. 2018; Mejia and Brouwer 2019).
Table 1: Hydrogen leakage summary
Table 1 summarizes the hydrogen leakage rates reported in the existing literature. Most of this literature cannot be cross-referenced, so some results were extrapolated from comparisons with similar technologies. Given that data on industrial facilities is missing, the leakage rate is assumed to be 0.5 percent. Production and delivery leakage are better understood than end-use leakage, data on which is largely absent. Table 1 enables a coarse estimate of the economy-wide hydrogen leakage rate by multiplying the hydrogen scale (tonnage) and the associated leakage rate (percentage). The summarized leakage rates are for the current situation (2020) and are used as a basis for estimates concerning the high-risk case by 2050, which assumes that the hydrogen leakage rates will not drop over the next three decades (i.e., the leakage rate will remain the same). Another set of leakage rates for the 2050 low-risk case is assumed to represent the technical/regulatory improvement (generally divided by two), leading to a lower risk compared with 2020.
Economy-Wide Leakage Risk Summary
Figure 2 shows the results for economy-wide hydrogen leakage in terms of both tonnage (Mt) and percentage (of total hydrogen produced). The total economy-wide leakage for 2020 is estimated to be 2.4 Mt or 2.7 percent. This relatively low result is driven by both the scale of hydrogen demand (approximately 90 Mt/yr) and a generally small leakage rate assumption for industrial end uses.
The 2050 economy-wide leakage rate and total tonnage amount are higher than those for 2020 because the scale of the hydrogen economy will be much broader (528 Mt/yr), and certain leaky processes will be more widely used (if they were used at all) than they were in 2020 (see Figure 1). The leakage rate stands between 2.9 percent (low-risk case) and 5.6 percent (high-risk case), and the total leakage volume stands between 15.3 Mt and 29.6 Mt. This can represent a non-negligible contribution to global warming and up to a $59 billion/yr value loss of hydrogen (assuming $2/kg-H2).
Figure 2: Economy-wide hydrogen leakage by process, 2020 and 2050
Detection, Monitoring, and Prevention Technologies
Hydrogen sensors, leak detection, and other safety infrastructure and techniques are still not at the scale of commercial production required to cover desired application scenarios. As the market has begun to adapt to meet new demands for hydrogen use, however, several technologies have been developed or are being refined to meet the challenge of fast, reliable hydrogen leakage detection across a range of production and fueling environments.
The highly flammable nature of hydrogen-air mixtures at concentrations above 4 percent and the conditions under which hydrogen is stored and transported require specific and concrete goals in the realm of hydrogen sensors. The DOE has set targets for hydrogen sensors using the parameters of accuracy, response recovery time, detection limit, ambient humidity, temperature, and pressure. After more than a decade of research, these targets have not yet been met (Granath 2015), but technology is improving, and several types of sensors are now available for production facilities, pipelines, and indoor and outdoor use.
Table 2: Performance targets for hydrogen sensor development
Some of the simplest and most effective methods of hydrogen detection (detection tape and smart coatings) have been developed over the past few decades with input from several research and engineering institutions. The National Aeronautics and Space Administration (NASA), one of the largest consumers of liquid hydrogen in the US, uses hydrogen extensively in its space shuttle program as a rocket propellant and to operate electricity-generating fuel cells. A leak in the space shuttle Endeavor in 2007 led to research and development on chemochromic tape. Patented in 2014, this new technology changes colors in less than three minutes and at concentrations as low as 0.1 percent hydrogen in the air (Granath 2015), well below the combustion threshold of 4 percent (Darmadi, Nugroho, and Langhammer 2020).
Further research into detection tape and smart coatings has ensued through public-private research partnerships with the support of the US DOE Hydrogen and Fuel Cell Technologies Office and NREL. Made of a silicone base, the chemochromic detection tape relies on partial oxidation of a transition metal oxide, resulting in a change in color in the presence of hydrogen. The tape can be readily used on flanges, welded seams and joints, rigid pipelines, and flexible tubing, as well as in indoor and outdoor hydrogen fueling stations and production facilities. Though lab testing is ongoing, the tape has been shown to respond under conditions of continually changing temperatures and humidity and to be UV resistant (US DOE 2016).
A similar technology is a thin film, vacuum-deposited pigment that changes color and resistance in the presence of hydrogen and can be used with wireless radio-frequency identification sensors for remote detection. Testing of this technology is likewise ongoing, but preliminary results indicate that it has a slightly faster response time and a slightly less durable pigment coating (Lee et al. 2015).
The preceding discussion alludes to several key considerations in developing hydrogen-sensing technologies: What is the precise concentration of hydrogen required for detection to occur? What ambient conditions are necessary in terms of temperature, humidity, and background gas composition? What is the working lifetime of the sensor technology?
Other methods and devices are also in use, including thermal conductivity, semiconducting oxides, ultrasonic physical principles, and drive hydrogen detection. These technologies may have potentially longer working lifetimes but require skilled operators or continual maintenance and upkeep to function properly.
A solid-state sensor has been developed that is capable of continuous monitoring and assessment of a cumulative, yearly leakage rate. Consisting of a metal hydride thin film and a microelectromechanical system (MEMS) structure with a palladium-nickel capping layer, this technology has demonstrated subsecond response times to 0.25 percent hydrogen in air and sensitivity to hydrogen concentrations below 200 parts per million (ppm) (DiMeo et al. 2006). Over the past decade, optical gas imaging cameras have come into use for leak detection, and hydrogen applications are being tested. Generally, CO2 is added to the hydrogen as a tracer gas in concentrations of less than 5 percent, after which the camera visualizes the leaking tracer gas at its source as the leak occurs (Beynon 2015). This technology is useful in outdoor applications, but factors such as dispersion conditions, wind direction/speed, plume polarity, ambient temperature, and background complexity can affect the accuracy of the camera detection and must be considered (Zeng and Morris 2020).
MEMS are currently used to detect hydrogen leaks from electronic products such as mobile phones with a detection limit of 10–500 ppm (Darmadi, Nugroho, and Langhammer 2020). This low detection limit could have implications for the immediate detection of leaks in production facilities if the technology could be transferred to and applied in industrial facilities on a large scale. Nanostructured palladium transducer materials are capable of very high sensitivity and fast detection for hydrogen-air mixtures, but more research is needed to bring them into the consumer realm.
Pellistor sensors, which come in two subtypes (catalytic and thermal conductivity), use the differential resistance of ceramic pellets to determine changes in gas concentrations. Coated with supported palladium, these sensors have been used to detect hydrogen at levels of 0.1–2.0 percent in the air at atmospheric pressure, though the accuracy of their response is reduced when the pellistor overheats (Jones and Nevell 1989). Like other more complex hydrogen leakage technologies, pellistor sensors represent a promising area but will need more testing under controlled conditions before they can be applied widely in commercial settings.
Other notable technologies include electrochemical sensors that use a liquid electrolyte, mass spectrometers, and gas chromatographs. These tend to be affected by varying temperatures or have long response times that may make them challenging to use in commercial settings, but research is ongoing. For indoor applications in places such as storage areas, portable, handheld hydrogen gas sensors offer ease of use and have been demonstrated to detect hydrogen at a minimum of 550 ppm (Mandelis 2013).
Review of Current Regulations
Production, Transportation, Delivery, and Storage of Hydrogen
In 2020, several countries with ambitious decarbonization goals and a desire to be part of the global hydrogen market announced new national hydrogen strategies. These strategies are currently outpacing the development and enforcement of hydrogen-specific regulatory frameworks and policies (e.g., safety codes and protocols, infrastructure standards, best practices, and certifications) for the production, transportation, storage, and use of hydrogen.
Although international standards for hydrogen use have been developed by the International Organization for Standardization, the International Electrotechnical Commission, and the European Industrial Gases Association, most of the countries that have announced national hydrogen strategies and roadmaps lack comprehensive and robust regulatory frameworks and oversight bodies to support their transition to hydrogen economies. A summary of the existing landscape of hydrogen regulations in major hydrogen markets can be found in the appendix (see Table A1).
Notably, South Korea and Japan were first movers in the nascent global hydrogen market back in 2017. South Korea holds the additional distinction of introducing the world’s first “hydrogen law” (Economic Promotion and Safety Control of Hydrogen Act 2021) to support its domestic and international hydrogen ambitions. In the United States, both public and private sector stakeholders are looking to the Federal Energy Regulatory Commission (FERC), Pipeline and Hazardous Materials Safety Administration (PHMSA), Department of Energy (DOE), and state and local regulators to lay the regulatory groundwork for a well-functioning national hydrogen ecosystem.
Countries seeking to develop well-rounded hydrogen economies—such as Finland, Norway, and Spain—will need to expand their existing (gas) regulatory frameworks to include hydrogen, while others such as Belgium, Chile, France, Germany, Morocco, and the United Kingdom will need to propose new laws and policies to accommodate their hydrogen goals. Despite several encouraging developments in some European Union (EU) countries and sectors, the EU as a whole lacks a comprehensive regulatory system to attract the requisite financing for establishing an EU-wide hydrogen economy as part of meeting the EU’s ambitious 2050 decarbonization goals. Developing this system will require a massive, well-coordinated effort. Other countries aspiring for regional or global hydrogen dominance—such as Australia, China, Denmark, India, Mexico, Russia, Saudi Arabia, and the United Arab Emirates (UAE)—will need to develop dedicated hydrogen laws, bodies, and policies to provide the necessary oversight for pilots, demonstrations, hydrogen hubs, and the full-scale production, transportation, storage, and application of hydrogen, in addition to careful monitoring of hydrogen leakage.
Presently, with very few exceptions, most aspiring leaders of the emerging global hydrogen market lack the dedicated legislation, regulatory frameworks, and internationally recognized standards to be considered best in class in the global hydrogen economy.
Findings and Recommendations
Finding 1: There is almost no data on and regulation of present hydrogen leakage rates and risks beyond required safety management. Hydrogen leakage data is not available for many industrial production and application processes. Most sources are not cross-referenced for those processes where leakage data is available but are rather simulation based and sometimes extrapolated from similar studies. Moreover, the data does not include device-level analysis and therefore cannot support bottom-up analysis, which is the typical way of assessing economy-wide, aggregated leakage rates. The current literature does not provide a clear understanding of the actual status of hydrogen leakage today.
Finding 2: Few technologies are available for hydrogen leakage detection and monitoring. Few commercial products have been identified to support hydrogen leakage detection, a step that is essential to fully understanding the current and future situation. This market shortage is partially due to lack of regulation: many countries have not developed dedicated legislation and regulatory frameworks for hydrogen production, transportation, storage, and end use, including in regard to hydrogen leakage monitoring. The need for more commercial products may be exacerbated by the expansion of the hydrogen economy, especially distributed sources such as fueling stations, fuel-cell vehicles, and end-use appliances.
Finding 3: Hydrogen leakage seems to be concentrated in a few key processes. By 2050, green hydrogen production, transportation, and storage (both pipeline and trucks); road transport vehicles; electricity generation; and chemical synthetic fuel production are expected to become the major sources of leakage. Together, they would contribute 77 percent of economy-wide hydrogen leakage. The main reasons for this large contribution are their broad scale (chemical and synthetic fuels production), high leakage risks (road transport vehicles, truck transportation, and storage), or both (green hydrogen production and pipeline transportation and storage).
Finding 4: Initial analysis suggests an increased risk of higher economy-wide hydrogen leakage rates in the future chiefly from new production and delivery expansion. Many key leakage processes for 2050 scenarios do not exist in the current hydrogen system. With the expansion of the hydrogen economy, the scaling up of production/use and deployment of new processes will increase the chance of leakage and therefore risk levels. The 2050 high-risk scenario will lead to a 5.6 percent economy-wide leakage rate. In short, hydrogen leakage is expected to be a challenge for the hydrogen economy.
Recommendation 1: Develop research and data-gathering programs to better understand the existing hydrogen systems. A lack of understanding of the current hydrogen system and the significance of leakage prevents the development of realistic solutions and appropriate regulations. The current hydrogen system is mostly based on industrial production and applications, and the research and data gathering on leakage that is required will likely be impossible without support from industrial partners. In order to understand and rigorously estimate the scale of hydrogen leakage, new regulations and policies should emphasize hydrogen leakage detection.
Recommendation 2: Require monitoring programs for new hydrogen pilots and scale up programs to assess the leakage risk of new processes. In the future, the real leakage risk will likely be new processes such as green hydrogen production, fuel-cell vehicles, and dedicated hydrogen deliveries. If the goal is to address this potential leakage, monitoring programs will need to be implemented for all new processes at the production, delivery, and end-use stages. Active control of these processes through regulations and policies before they scale up can help reduce risks and potential economic losses associated with the future hydrogen economy.
Recommendation 3: Devote special attention to certain key processes that demonstrate potential to be scaled up or to address high leakage risks. Based on the available data at this stage, it is estimated that a handful of processes identified in Finding 3 would contribute to an estimated 77 percent of total hydrogen leakage in the 2050 scenarios. Significant resources have been dedicated to scaling up the production and use of hydrogen but not to controlling leakages in the process. To the extent that leakage estimates are confirmed and leakage is concentrated around key processes, research on leakage prevention and regulations for a few key processes will have greater impact than that for others if the goal is to effectively reduce overall hydrogen leakage.
Recommendation 4: Expand support for research and development programs on hydrogen leakage detection, prevention, and mitigation. There is insufficient research on how to prevent and mitigate hydrogen leakage. Moreover, the commercial products that currently exist for this purpose do not meet the requirements of device level, high sensitivity, and distributed small hydrogen leakage source detections. If the goal is to develop a thriving hydrogen economy without hydrogen leakage, research and development funding should be prioritized for hydrogen leakage detection, prevention, and mitigation, with special attention dedicated to bringing technologies currently at the research level to the commercial level.
Table A1: Current regulations for the production, transportation, delivery, and storage of hydrogen
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