Testing with HE is more accurate due to the scarcity of helium in the atmosphere. Nitrogen is typically used as a carrier gas only. Test with helium can allow detection of leaks down to 100 SCF/year.

In any event even if leak tight any flange/connections will be considered as a zone 2 potentially explosive atmosphere and if hydrocarbon only, then the main risk would be associated with explosion/jet fire.

Regards

I'm not really sure why it has been determined that due to no H2S there is no requirement for helium to be used.  There isnt really any link.  Helium is used for several reasons, it is easy to detect using instruments as there is virtually no helium in the atmosphere, it is actually mined rather than taken from the atmosphere.   Most of the atmosphere is nitrogen so its all around us all the time.  Helium has very small molecules so will find smaller leaks.  This is why helium ballons always deflate within a day or two, the gas is leaking through the walls of the ballon, so it will find the tiniest leak.  It is also inert so will not react with anything it comes into contact with.  So very good for leak testing and used as a mix with nitrogen as helium on its own is very expensive.