Hydrogen+. Can you tell us about your work regarding safety and industrial risks related to hydrogen?
Alban Mahon. For eight years, I have been working in the field of quantifying the consequences linked to accidental phenomena. This includes, for example, fires, explosions and releases of toxic products into the atmosphere. The objective of these calculations, and therefore of these studies, is to determine the safety distances to be established based on thresholds predefined in official documents and to size the appropriate prevention and protection measures. This may concern, for example, thermal flows in the event of the release of flammable products or a fire. Any constraints linked to the environment of the industrial site are also taken into account within the framework of these studies.
Since 2021, I have also been working on the Airbus zero-emission aircraft project. I bring my knowledge and expertise on the phenomenology linked to the use of hydrogen as fuel. This of course concerns the question of establishing safety distances between on-board equipment, but also all the impacts linked to fuel modification. In other words, are the requirements currently followed for the use of kerosene still applicable or is it necessary to evolve them specifically for the use of hydrogen? We are therefore assessing all the impacts of this change as well as the consequences in terms of safety in the context of hydrogen storage and distribution.
Regarding the methods and tools currently used in the industry, the assessment of risks and safety distances is based on several ranges of models, from the simplest to the most complex. The latter require a representation of geometry in 3D and allow fine resolution of physics through the use of computers, or even supercomputers. These more complex models allow us, for example, to take into account all physical phenomena without having to resort to strong hypotheses.
The methods used depend in particular on the objectives and issues of the studies. In the context of industrial or airport infrastructures involving hydrogen, methodologies based on experimental correlations are often used. This includes taking into account more or less dimensional hypotheses depending on the maturity of the project in question as well as the engineer’s feedback. It is also important to note that the majority of models used were mainly developed more than 20 years ago, in connection with the use of hydrocarbons.
Therefore, the development of the hydrogen sector must be accompanied by the updating of these calculation methods in order to account for the specificity of hydrogen (extremely flammable product, with specific physicochemical properties) or new conditions of use (cryogenic hydrogen storage, high distribution pressure, etc.).
For example, the storage of hydrogen in a liquid form, with a temperature close to absolute zero, entails the specific consideration of the cryogenic impact.
This updating work is a current consideration for many stakeholders and new models and best practices related to hydrogen are regularly published. Part of our work therefore consists of exploiting these new possibilities and establishing new calculation practices.
However, certain issues related to hydrogen are still poorly understood. This is for example the case of detonation phenomena which are accompanied by shock waves and high combustion rates.
These purely physical considerations are at the heart of the concerns of certain laboratories and their research will undoubtedly fuel future versions of models or the development of new calculation approaches.
Finally, it is important to remember that the critical eye of the engineer responsible for these estimates is essential in order to prudently evaluate the safety distances between the infrastructures and the surrounding populations. The constraints mentioned above can, however, be significantly different in the case of a product where security is at the heart of development. This is for example the case of the hydrogen plane.
Can you tell us about your work on the hydrogen airplane project?
Generally speaking, future airport infrastructure should be distinguished from the aircraft itself. For the former, approaches from industry are used with a view to defining safety distances for both passengers and airport staff. For the aircraft product, the constraints are very important if we want to maintain the current level of safety. It is therefore necessary to push the understanding of physical phenomena to the maximum in order to be able to propose a design that meets all the constraints, including those of safety.
Unlike the development of the latest aircraft (A350, A320neo), for the hydrogen aircraft, we are starting almost from scratch. The approach implemented consists of evaluating whether the requirements defined for kerosene are still valid for hydrogen. This approach makes it possible to identify the points on which significant development is necessary and reveals the need for consolidation of knowledge. For example, is the thermal attack of a kerosene flame similar to that of a hydrogen flame or is it different? Will the requirements on structures capable of containing a kerosene fire be different for hydrogen? This important work is being carried out at the moment and I am actively taking part in it.
This work is also accompanied by updates and development of new tools whose validation needs are carried out in parallel by the implementation of experimental tests and the study of scientific publications. Research focuses in particular on several areas such as hydrogen combustion, structural resistance, cryogenic aspects, etc. The use of hydrogen can be seen as a challenge because it enters the realm of extremes, whether cryogenic storage temperatures or more violent combustions/explosions. This is a real work of exploration in the field of physics.
The objective is therefore to push research further to understand all the accidental phenomena that can occur on a hydrogen-powered aircraft. This increases the spectrum of our knowledge of the factors that can lead to risks. Ultimately, this exploration work allows us to anticipate possible risks, to avoid them and propose solutions, designs or infrastructures with a high level of security.
