I was thinking that that despite you not being able to smell the gas some may have been present setting off the "alarm bells" however if they thought it was dangerous why send it back ...??? Even if you do get through to customs [as I have in the past] you really end up speaking to someone on a computer , they will say yes its here, and sorry I cant help you further than that ..Pfft!  I had a set of special wire twisting pliers sent, harmless, yet ended up in customs for weeks on end.. A lady walked up my driveway saying I think this package might be yours  ,of course on top of the delay they sent it to the wrong address and it arrived a day late for what I needed it for ..Great!
Its amazing how sensitive those machines can be at picking up drugs , fumes, explosives etc.. Just ask me I got detained at the Long Beach Airport... Well I got worried when after several inspections they invited me into the small room ..  ; o 0

"Came too close to dying to stop living now!"