Where will it end?

Sooner or later someone is going to propose neutron activation scanning; after all, all explosives seem to contain nitrogen, so if we can detect nitrogen....

Except food nearly always contains proteins, which contain nitrogen. Excuse me sir, you can't take those foodstuffs through security.

People are also made of proteins.

Best of all, supposing there was an explosive that didn't contain any nitrogen ... how about ... triacetone peroxide? That 'Mother of Satan' stuff at the centre of the 2005 bombings and the liquids-on-aeroplanes scare?

So, no neutron activation scanning then, which is probably just as well. But I bet some fool is going to propose it anyway.