D2.4 The risk of not odourising hydrogen

Purpose of this research
This report is part of Work Package 2: odorization of hydrogen. The aim of this work package is to fill some knowledge gaps related to the introduction of an odorant for hydrogen distribution. The specific research goal described in this report is to determine the risks of non-odorization of hydrogen and an inventory of alternative detection methods of hydrogen gas leaks.

Risks of non-odourization in gas distribution
When hydrogen is distributed to the built environment through gas pipelines as a collective energy carrier, it is imperative that the hydrogen is odourised to minimize the risk of escalating from a hydrogen gas leak to an incident. It follows from a study by Bilfinger Tebodin that in the distribution of natural gas, the barrier that odorization creates to prevent the escalation of a gas leak to an accident such as fire, explosion or suffocation is effective in 98% of the cases. Not odourising means that the chance that a gas leak will lead to a serious incident, increases by a factor of 50. In 2020, more than 25,000 natural gas air reports were made in the gas distribution network in the Netherlands. In the absence of the odorant, a large part of these disturbances would have gone undetected and could have escalated into an incident.
There is no reason to believe that this will be any different in the case of hydrogen distribution.

Choosing a hydrogen odorant
A number of studies state that an odorant for hydrogen should have at least the same alarming effect as the odorant used for natural gas. This doesn’t mean that it must necessarily be the same odorant that is in use for natural gas and that is publicly known. Studies conducted as part of the Hy4Heat program warn that changing the type of odorant may pose a risk because the public's response to a new gas smell may be different. When choosing a different odorant, an extra effort will have to be made to familiarize the public with the new odorant.
The first experiences with the odorization of hydrogen are positive and the smell of the odorant in hydrogen is comparable to the smell in natural gas.

Alternative and additional safeties
Static hydrogen gas detectors can play a role in the safety of hydrogen distribution, but there is no uniformity about this in the literature sources found. According to the IFV (Instituut voor Fysieke Veiligheid), hydrogen gas detectors can be used in confined spaces to replace odorization. However, there is concern about the maintenance of these detectors and where they should be placed. No statements are made about the role of hydrogen gas detectors in the hydrogen gas distribution network.

Conclusion
The main conclusion from this literature review is that not odourising distributed hydrogen will lead to a significant increase in the number of hydrogen gas accidents if no other additional measures are taken. At the moment, odorization of hydrogen as a collective energy carrier is a necessary measure due to the lack of a worthy alternative to achieve the same safety level as with odourised natural gas.