Schneier on Security

Clive Robinson • May 28, 2008 2:25 PM

Any one remember “Aunt aggies bomb factory” during the 1970’s.

Well their hands were swabed and came up positive for explosives.

Turns out they had been using old playing cards with a nitro celulose finish (still quite common).

And for those that are realy realy old the exploding billiard balls?

Turns out that various compounds of nitrogen and celulose where the equivelent of the “plastic of their era” and turned up all over the place such as piano keys, billiard balls and even ash trays and knife handles. Oh and of course “celuloid” film stock.

All of these every day items many still in use will leave traces on your hands that will show up as possible explosives on swabs several days after handaling them.

Also don’t shake hands with anybody with a dodgy ticker they might have used their NG spray recently (yup it’s Tri Nitro Glycerin or blasting oil as used for making dynamite).

There are so many ways to come into contact with “nitro compounds” that it is going to be worse than cocaine on twenty dollar bills.

What is needed is not a more sensitive test but a more discriminating test otherwise the false positives are going to be something like 5-15% of the population.