Pre-normative Research On Hydrogen Odorisation: Enhancing Safety And Detection Along The Hydrogen Value Chain

Expected Outcome:

In the European Union, depending on the Member State, natural gas is odorised, primarily for safety reasons, according to ISO16922^[1]. This standard provides guidelines for odorising natural gas and other methane rich gases. However, with a switch to hydrogen, new risk mitigation strategies need to be developed or existing adapted.

With the switch from natural gas to 100 % hydrogen, especially in hard-to-abate industries, safety measures have to be established. Historically, odorisation proved to be an easy applicable safety measure.

Due to different requirements for hydrogen, such as purity and physical properties of the molecule, different odorants have to be used for hydrogen than the ones currently used for natural gas. Therefore, odorants, that are non-toxic and environmentally benign and that provide sufficient olfactory warning, need to be developed and tested. The olfactometric properties should be similar to what is already known and trigger a similar reaction as to natural gas. Especially with sensitive end-users in mind, possible de-odorisation might be needed as well, if the applied odorant is not tolerated by the end-use applications.

A thorough data analysis based on literature as well as already conducted research, such as for example Ready4H2^[2], Hy4heat^[3], Met4H₂^[4], sets the basis for testing new and old odorants. The focus should be on the odorant in hydrogen, for example masking effects, degradation and other technical aspects.

Project results are expected to contribute to all of the following outcomes:

• Providing data on different odorants or chemical families of odorants to regulatory bodies to ensure that hydrogen gas grids and appliances meet safety and performance standards throughout the European Union, including the tolerance of materials used that come in touch with odorants (and its degradation products if any);
• Harmonised standards and guidelines to reduce over-conservatism and ensure consistent safety measures;
• Standard methods for odorisation and de-odorisation of hydrogen.

Project results are expected to contribute to the following objectives of the Clean Hydrogen JU SRIA:

• By 2030 hydrogen safety is understood and lived holistically and odorisation is one of the applied safety measures;
• By 2030 public awareness of odorised hydrogen is enhanced and the use of hydrogen as an energy carrier widely accepted in the EU, as a target group especially the non-experts.

Scope:

While the goal is to have an entirely decarbonised gas grid by the end of 2030, safety measures are needed when switching to 100 % hydrogen. For a safe operation, pipeline components not only need to be checked for hydrogen tolerance, but also whether they tolerate the odorants themselves. Pre-Normative Research (PNR) and the development of regulations, codes and standards (RCS) require an open communication and knowledge transfer across project boundaries and beyond project terms. Generation of experimental data, collaboration and coordination with international partners and stakeholders are essential to ensure that this goal is achieved in the EU and even worldwide.

The warning scent of an odorant should be detectable at very low concentrations. Therefore gas-air-mixtures in indoor areas should reliably be olfactorily detectable at 20% of the lower flammability limit in air²⁵⁰. The lower flammability of hydrogen is 4%, therefore the odorised hydrogen should be detectable at 0,8% in air. Olfactory tests in laboratory scale should therefore be executed to ensure the desired detectability.

The development and characterisation of new odorants is encouraged but not mandatory. Additional to this data analysis, literature research for hydrogen detection methods shall be provided, assessing general application possibilities to give a full picture of available leak detection methods. The odorants found suitable for testing should be subjected to tests according to DIN EN ISO 13734^[5] and the gathered data publicly shared according to FAIR principles. Additionally, the odorant(s) should be thoroughly analysed and characterised including, but not excluding any other analysis, such as the following:

• Chemical characterisation of the odorant molecule (if already known, based on literature) for example by using GC-MS/MS, NMR and elemental analysis for new compound;
• Provide analytical methods to quantify the lowest concentration (ppb/ppt levels) of the odorant/s detectable by olfactory test, as well as methods suitable for controlling fraud in the odorant employed at hydrogen (i.e. using tracing analysis);
• Stability tests of the odorising molecule and characterisation of possible degradation and transformation products while providing tracing methods to quantify the degree of degradation of the odorising molecule by relevant analytical methods;
• Assessment of in-silico toxicity of the odorant/s at different concentrations, and eventually of the transformation products/degradants;
• Absorption/permeation tests for the odorant (including the degradation molecules (differentiation for example via chromatography)) in hydrogen for different polymers (pipes or seals) and examination of possible material alterations ;
• Impact on end users’ system in term of performance or environmental impact (i.e., fuel cell, combustion, chemical use as for fertiliser etc.).

The odorant itself should be tested in a close to real-world environment or conditions (test bed), to ensure it is tolerated by the materials used for example in pipes, compressors, valves and other materials getting in touch.

With regards to safety, proposals should ensure that the odorant and or its degradation molecules do not enhance hydrogen embrittlement, hydrogen permeability through polymers or other ways of hydrogen corrosion or be corrosive themselves. Tests could be performed for example after ASME B31.12^[6] or be tackled via modelling / numerical studies.

Due to some sensitive hydrogen appliances, at least a validated strategy for the removal of odorant molecules for sensitive appliances, either with fitting absorbents, adsorbents, membranes, PSA or other, should be demonstrated. The purity of the de-odorised hydrogen should meet the requirements according to ISO 14687^[7].

Hydrogen odorisation takes place in specific parts of the transmission and distribution network, usually at feed-in of the gas, but sometimes at compressor and pressure regulator stations. To ensure safety throughout the entire hydrogen supply chain, it's important to study the quality of the hydrogen-odorant mixture, especially how it moves through the pipes of the different networks e.g., transportation or distribution. This involves modelling and simulating how the mixture flows under different pressures and different flow velocities. By doing this, it can be understood how the odorant spreads, including how its concentration changes over time and how much of it is lost at different points in the network.

The expected results, aim to support the definition of regulatory standardisation frameworks. Given the scope of this topic, the involvement of formal standardisation bodies as part of the consortia is encouraged, with the aim of facilitating the uptake of the project results. Furthermore, participation of gas distributors and regulatory institutions, with practical experiences concerning the odorisation of hydrogen, is encouraged.

Proposals should pay special attention to the dissemination of the results and enhance exchanges with relevant stakeholders mentioned above, e.g via annual workshops and by working in synergies with others as follows.

The proposal should complement, built and create synergies with relevant projects. In particular, synergies should be foreseen with the project supported by the European Partnership on Metrology, EURAMET, Met4H2^[4], where standards for sulfur-free odorants were developed with support of the hydrogen distribution sector.

Furthermore, proposals should create synergies and collaborate with relevant recent and new developments on regulation, codes and standards including but not only, the project HyQualNet, whose results should be taken into account ^[9].

For additional elements applicable to all topics please refer to section 2.2.3.2

[1] https://www.iso.org/standard/83835.html

[2] https://www.ready4h2.com/

[3] https://www.hy4heat.info/

[4] https://met4h2.eu/

[5] https://www.iso.org/standard/56767.html

[6] https://www.asme.org/codes-standards/find-codes-standards/b31-12-hydrogen-piping-pipelines

[7] https://www.iso.org/standard/82660.html

[8] https://met4h2.eu/

[9] https://www.cencenelec.eu/media/CEN-CENELEC/News/CallForTender/Documents/2025/HyQual/hyqualnet_opencallfortender.pdf