Hydrogen incident statistics 1999-2023
Hydrogen economy as a key to achieving climate goals of end-to-end decarbonisation poses a number of fundamentally new challenges for mankind. The unique physical and chemical properties of hydrogen, including its lowest molar mass, minimum ignition energy, wide range of ignition limits and high energy density place the safety of hydrogen production, distribution, and utilisation at the forefront. This text briefly reviews retrospective studies of available hydrogen accident statistics using different analytical approaches and databases, covering events that occurred mainly in the USA, France, Japan from 1999 to the present. The purpose of this publication is to clearly confirm the high urgency of hydrogen safety problems, the most frequent problems leading to accidents, as well as to draw attention to the need for scientific study of the behavior of significant volumes of hydrogen, including under pressure in mixtures with air in different concentrations.
The first research (Yang et al. Tsinghua University) statistics based on data from the U.S. Department of Energy for 1999-2019. The research funded by the Ministry of Science and Technology (MOST) of China, results entitled “Review on hydrogen safety issues: Incident statistics, hydrogen diffusion, and detonation process” http://doi.org/10.1016/j.ijhydene.2021.07.005. All event data for 120 incidents came from factories, governments, research institutes, and other institutions worldwide. Laboratories were the most accident-prone locations, accounting for 38.3% of incidents, followed by Hydrogen fueling stations and hydrogen-related Commercial facilities, accounting for 10.6% and 9%, respectively.

Further analysis of the details of laboratory incidents revealed that human error and equipment failure are two major causes of the incident. Equipment failure is the main cause of the incidents, accounting for 35.78%. In-stances of equipment failure include hydrogen leakage resulting from piping rupture, fitting, and valve failure. Human error and design flaws – 14,2% and 9%.

Piping/fitting/valves (38.2%),Hydrogen storage equipment (15.5%), FCEV and refueling systems (12.2%) are the hydrogen-related facilities that have been found to be most susceptible to failure. In particular, rupture of pipework and valve failure are the main manifestations of hydrogen incidents. According to further analysis of the facility problems, hydrogen embrittlement and equipment fatigue are the main causes of incidents. Failure of the storage equipment occurs mainly due to two causes: damage to assembled in-cylinder taps due to valves such as regulators, and failure of ties securing the hydrogen cylinder.

According to an analysis of the damage and injuries resulting from these incidents, the damage is mainly related to material loss and accounts for 41.83%. In addition, 10.27% of all accidents will result in human injuries and 5.32% will result in fatalities. When compared to the injury and fatality rates for gas incidents (10.87% and 2.65% respectively), although the injury rates are almost equal, the fatality rate for hydrogen incidents is twice as high as for gas incidents. To be fair, statistics studied only two fatalities in one incident belonged to professional chemists who made a fatal error while attempting to correct a previous error in refueling a cylinder with hydrogen.

The scientific study of the сhinese authors, based on the statistics of hydrogen incidents, further investigates the diffusion, leakage and behavior of hydrogen jet in mixtures with air, including the problems of ignition, self-ignition, combustion stages, combustion-to-detonation transition, and thermobaric effects. For a number of key issues, such as diffusion and leakage, the researchers note the need to confirm the results of mathematical modeling with experimental studies.
In looking at the potential risks of large-scale hydrogen leaks, scientific assessments of their climate impacts should be considered. https://www.nature.com/articles/s43247-023-00857-8
Reacting with other greenhouse gases, including methane, ozone and water vapour, hydrogen has an unrivalled binding rate, altering established patterns of chemical reactions and physical processes in different layers of the atmosphere. In general, the effects of hydrogen on the atmosphere and climate are diverse and poorly understood, but studies of its reflective potential as an independent gas have raised the GWP100 index of hydrogen to 4.5-8 in mean values with the highest confidence, and with indirect factors up to 12 depending on the measurement technique and atmospheric layer. Thus, hydrogen leaks are a source of atmospheric pollution and will fall under the supervision of regulatory authorities.
Though many experiences have been obtained in the design and running of specific hydrogen utilization systems, new seintific data about the hydrogen and hydrogen system properties is desperate needed. To mitigate such an issue, some valuable data collecting and sharing platforms have been established, e.g., HIAD and HyRAM. Based on these collected data, reliable models can be established in combination with physical based information, enabling the quantitative risk assessment of both existing and under constructing systems. Incidentally the first repository of data from more than 700 incidents recently received an update that led to the release of a review last year entitled “Statistics, lessons learned and recommendations from analysis of HIAD 2.0 database”. https://doi.org/10.1016/j.ijhydene.2022.03.170
This study provides an excellent overview of American and European experience in collecting information on hydrogen incidents. The authors, who are members of the European Hydrogen Safety Panel (EHSP) of the Joint Fuel Cell and Hydrogen Programme (FCH 2 JU), assessed and classified each of the 576 incidents found to be statistically significant.

Most оf events contained in HIAD 2.0 occurred in the period from the 1990s to the 2000s. One of the causes of reduction of the incidents after 2000 is attributed to the improved safety design and operative provisions in chemical and petrochemical industries. Other causes might also include under-reporting or delay in reporting of the events even though there is no evidence to support this.

Geographically as illustrated more than half of the considered events occurred in Europe while one quarter occurred in North America. Asia accounts for less than a sixth of the events while the events from other regions account for only 2%. It should be borne in mind that the information was collected from open sources, so this geographical distribution should not be generalised as indicative of real geographical distributions of historical events in the world.

Fig.4 illustrates percentages of events initiated by hydrogen or non-hydrogen systems (outer circle) and those related to different consequences (the inner circle). The outer circle illustrates that the majority 75% of the events were initiated by hydrogen systems. The inner circle reveals that apart from the 15% unignited releases and 6% near misses, hydrogen was ignited in 79% of the events with 48% involving explosions. Excluding the events, which involved fires following explosions, 31% of the considered events involved only fires. A combination of reasons was attributed to the 15% unignited releases, including prompt termination of the unintended releases and the releases being very small, etc. The 6% near misses give a promising message that early detection and prompt mitigation of any potential releases can successfully avoid escalation of the event following an unwanted release.

As most incidents had multiple causes, the individual percentages add up to more than 100%. About half of the events were related to Organizational and management factors. Material/manufacturing errors are the second main cause with a share of 35%. Other main factors include Individual and human factors 29%, System design errors 27% and Job factors 14%. Only 11% of the incidents were related to Installation errors.
Six cause categories were adopted in the analysis. The first three are related to system design, material, manufacturing, and installation:
-System design error: The system was not properly designed for the operating conditions or the use of hydrogen. Examples include components not compatible with hydrogen, lack of ATEX components when required, the unforeseen occurrence of the hazardous gas mixture, unforeseen pressure or temperature loads, wrong type of solenoid/electromechanical valve selected, etc.
-Material/manufacturing error: Although the correct component was selected and implemented, it did not work properly due to material failure or due to a manufacturing error.
-Installation error: Although the correct component was selected and implemented, it malfunctioned due to improper installation or maintenance. For example, a thermally activated pressure relief device (TPRD) was not installed on a gas bottle or cylinder or installation instructions of a safety device were disregarded.
Another three cause factors relate to human factors, for which the definition of the Health and Safety Executive (HSE) includes three interrelated aspects: the job, the individual and the organization. In the Seveso Directive, “organisation” is referred to as “safety management system factors”. In several events, the root causes were traced back to the absence of adequate safety culture, clear instruction and staff training.
It is recognised that the definition of each of these categories can vary in different situations and by different analysts. To ensure consistency, the following examples were used by the authors to illustrate how they are classified in the subsequent analysis:
-Job factors: inappropriate design of equipment and instruments, design fault, missing or unclear instructions; poorly maintained equipment; high workload; noisy and unpleasant working conditions; constant disturbances and interruptions, etc.
-Individual/human factors: inadequate skill and competence levels; tired staff; bored or disheartened staff and individual medical problems, etc.
– Safety management system factors: poor planning, leading to the overstressed workforce; lack of safety systems and barriers; failure to learn from previous incidents; biased one-way communication; lack of coordination and clear definition of responsibilities; poor management of health and safety; poor health and safety culture. Several incidents showed poor or not updated operative and maintenance guidelines/instructions, especially in relation to external contractors.
This study was more practical in character, with each incident given a unique identifier to cite as an example to the practice guidelines. Therefore, no further statistics are provided.
In early 2023 NETL published a “Hydrogen Safety Review for Gas Turbines, SOFC, and High Temperature Hydrogen Production” https://netl.doe.gov/node/12813. It contains incident statistics compiled from the state resource h2tools.org. Figure 2 demonstrates the grouping of researchers Weiner and Fassbender (2012) by location type. It confirms laboratories as the leader, followed by incidents at hydrogen refueling stations, commercial facilities, power stations and hydrogen delivery vehicles (excluding the first category “misc”). Damage and injuries (Figure 3), Equipment involved in incidents (Figure 4), Probable causes of incidents (Figure 5), and factors contributing to the incident (Figure 6).


As seen in Figure 3, most reported hydrogen incidents have resulted in property damage and facility closures, with approximately 17% of incidents reporting minor or lost time injuries, as well as fatalities in 5% of reported incidents.

Figure 4 shows that roughly half of reported incidents have involved pressure vessels, piping, and valve systems, and to a lesser extent compressed gas canisters, electrical issues, and measurement sensor failures.

Figures 5 and 6 show that, for the reported incidents, equipment failure and human error (including situational awareness, training, improper maintenance, failure to follow established procedures, etc.) were either the probable cause or a contributing factor to the incident.
Notably, the US government laboratory review subsequently cites data from the study by Yang et al. 2021, with which we started this review, where hydrogen leaks, jet, hydrogen cloud, its ignition, combustion modes, and detonation are considered. Also in this review hydrogen is explicitly called an indirect greenhouse gas, and its negative impact on the atmosphere is explained in a separate paragraph. It also recognises the lack of understanding of the phenomena under study and the need for experimental verification of the mathematical models. Next, the NETL review focuses on safety of hydrogen turbines, solid oxide fuel cells and high temperature electrolysers. Very new data about technical risks in this field.
As can be seen, the economic circulation of hydrogen faces a set of challenges to ensure safe and sustainable operations. The main factors remain technical and design problems of specific units and assemblies, as well as human factor. However, statistics formally show a decline in the number of accidents, which inspires hope for the positive contribution of engineering and work culture. At the same time, the relevance of liquid hydrogen operations is growing, where the safety requirements and consequences of accidents are even greater.
Author-Serge Astafurov