I had my back pack with flight helmet questioned for an international flight PH to JB 18 months ago.
Apparently it returned 2 positive spikes for fertilizer based explosives, Ammonium Nitrate I guess, and another spike for smokeless rifle powder, and confirmed on re-test.
Got ushered off to a small room with 2 security chaps and 2 senior FA's.
Couldn't really explain it myself so I simply stated that most country blokes smell a bit that way, it's our lifestyle and blowing things up and shooting are perfectly valid and educational past times in the country. Although it did stump me a bit as I hadn't been near either product for ages.
They seemed pretty happy with that and I boarded my flight to JB.