With IR/UV detectors as commonly used in hydrogen vehicle station forecourt applications, what would be the expected size of any leaks and resultant jet fires? What about interference and the tendency for existing technologies to be shut down in situations where there could be false positives from background radiation, lightning, and sun reflection off a vehicle mirrors?

There are many manufacturers of multiple  types of flame detectors and it’s best to seek their input for the advantages of different types for specific applications. Regarding flame detector technology, UV detectors have been prone to false alarms from outside sources such as sunlight, lightning, and welding/cutting torches. The newer triple-IR detectors that are specifically designed and tested for hydrogen flames have been shown to be effective. These detectors are currently in use at many hydrogen systems for detecting both hydrocarbon and hydrogen flames. Also, flame detection will only detect a leak once the hydrogen is ignited.  It is difficult to assess the minimum leak size without specific testing at known hydrogen pressure and the distance of the detector from the leak