The paper presents an overview of the main results of the EC NoE HySafe activity to estimate an allowable hydrogen permeation rate for automotive legal requirements and standards. The work was undertaken as part of the HySafe internal project InsHyde.

A slow, long term hydrogen release such as that due to permeation from a vehicle into an inadequately ventilated enclosed structure is a potential risk associated with the use of hydrogen in automotive applications. Due to its small molecular size hydrogen permeates through the containment materials found in compressed gaseous hydrogen storage systems and is an issue that requires consideration for containers with non-metallic (polymer) liners. Permeation from compressed gaseous hydrogen storage systems is a current hydrogen safety topic relevant to regulatory and standardisation activities at both global and regional levels.

Various rates have been proposed in different draft legal requirements and standards, based on different scenarios and the assumption that hydrogen disperses homogeneously. This paper focuses on the development of a methodology by HySafe Partners (CEA, NCSRD, University of Ulster and Volvo Technology) to estimate an allowable upper limit for hydrogen permeation in automotive applications, by investigating the behaviour of hydrogen when released at small rates with a focus on European scenarios. The background to the activity is explained, reasonable scenarios are identified, a methodology proposed and a maximum hydrogen permeation rate from road vehicles into enclosed structures is estimated. The work is based on conclusions from the experimental and numerical investigations described by CEA, NCSRD and the University of Ulster in related papers.