Given the extraordinary number of explosive compounds you will a complete laboratory analysis of *every* liquid, powder and solid that goes on an aircraft.
That isnt practical.
Okay, remember, my point isn't that this is terrorist prevention. If a terrorist wants to take a plane down, they're most likely going to find a way. I'm more worried about "psycho nutjob" prevention with the lighters. Some are probably well-versed in chemistry, but most are more likely to be pyromaniacs.