Originally Posted by DCA TSO

As was said by Spiff above, ETD and ETP look for high explosives not low explosives (gunpowder, flash powder, etc.). The reason low explosives are ignored in explosive trace testing is because they require a substantial, high-strength casing (e.g., 3/8 steel pipe, etc.) in order to be explosive (i.e., there's 0% chance they're getting through x-ray or WTMD), and any device using them will be haphazard at best.