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 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.

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, 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.