All Blake has to do is spend 5 minutes in the same room. “Gunpowder Residue” has been shown to get onto everything, and into everywhere. It’s another forensic pseudo-science like voice-prints, hair examination, blood detection, lie detectors, bite-mark patterns, ear prints, handwriting analysis, podiatry, odontology, bullet tool marks, friction ridge analysis etc.
It’s chief value is in investigation, not in proof. Now they’ve got the gunpowder residue on Blake, what’s his excuse, and why didn’t he mention it before?
Gunpowder and high explosives aren’t the same thing. Gunpowder deflagrates, i.e. the reaction front progresses through the mixture at subsonic velocity. High explosives detonate, i.e. the reaction front progresses through the mixture at supersonic velocity. The chemistry is different. Most high explosives are nitrogen-rich, so that’s what most detectors are looking for.
I’m not a TSA agent, but my guess is that the explosives detection machines deliberately don’t look for gunshot residue. Shooting guns is a common enough hobby in civilian life that if the machines did detect GSR, it would probably be sidetracking a lot of passengers. In the US, you’re allowed to fly with guns and ammo in your checked baggage - which means gun owners will probably end up with some GSR on their hands merely from having packed those items before their trip.
If I recall my high school chemistry, a key ingredient of (traditional) gunpowder is potassium nitrate (saltpeter). Are you saying those nitrates involved are not sufficient to set off TSA detection? Which brings to mind - what about people who use a lot of fertilizer? The Oklahoma bomb was fertilizer and diesel fuel…
The vast majority of guns that people fire today, including virtually all premade cartridges, use smokeless powder, not black powder. Black powder is pretty much only used for black powder hunting season and replica or antique guns fired recreationally. It’s readily available at gun stores, but is a specialized hobbyist thing, not a general purpose thing. Smokeless powder may well set off bomb detection (it’s sometimes used to make pipe bombs), I’m not sure about that, but wanted to clarify that black powder is not that common to encounter.
It looks like smokeless powder does have nitrogen-bearing compounds in it. It may be that someone who has recently handled unburnt smokeless powder (like a competition shooter who loads their own ammo) would trigger a bomb detector, but as Pantastic notes, most gun owners don’t handle unburnt smokeless powder - they handle pre-assembled rounds, and they handle firearms that have GSR on them (which probably doesn’t have much unburnt powder).
People who handle large quantities of fertilizer might indeed be subjected to extra scrutiny if they set off the explosives detector. I don’t think triggering the detector means you don’t fly, it just means you get a lot of extra questions, a pat-down, and a careful inspection of your carry-on (and probably also your checked baggage). Unless you’ve got a “get out of jail free” letter like my acquaintance.