In that case, what could somebody possibly put in that would give the machines a false positive? I can’t think of anything (other than cocaine or heroin, since they are all ‘CHON’ (carbon, hydrogen, oxygen, and nitrogen) molecules. Regardless, those positives wouldn’t exactly be false. Are there other CHON compounds that are legal to take on a plane? In other words, on what basis are you disagreeing?
ETA: That also has a molecular mass in the 200+ g/mol range.
Ah, but what if they put in a security checkpoint before the security checkpoint? Then they’d be 100% terrorist proof!
I don’t know, but false positives do occur. For obvious reasons, the TSA isn’t exactly publicizing the sorts of things which false trigger so I haven’t found any specific examples, but it’s not unreasonable to imagine that major news media outlets have the resources to discover such things.
OTOH, the new agency which “smuggled” in a box with the word bomb written on it made me :rolleyes:.
A three pound block of cheddar cheese, or chocolate. Take your pick.
Don’t ask me how I know this. 
No doubt. The point I’m trying to make is that you can’t really fake a bomb, and then not get a false positive, and say you were able to sneak a bomb through. It simply doesn’t make sense. It’d be like putting a bag of oregano in your luggage and then claiming you were able to sneak fake pot through.
Was it discovered by an x-ray machine they send the bags through? I can imagine them looking quite similar on one of those types of machines. I’m not as familiar with that type, though. All of my research has been on equipment and methods that look for specifically explosives and illicit drug detection. Maybe these fake bombs are just wires stuck into cheese? 
Only about eleventy bazillion of them. Almost anything you can think of that originally comes from a living thing is primarily CHON. And 200 g/mol is positively tiny, as organic molecules go.
For example, CHUDs are made of CHON.
It’s people! Soylent CHON is made of people!
You joke, but I remember an incident a few years ago where someone pulled a gun at the ticket counter and some people were saying that we needed to move the security to the front doors of the airport.
Obviously we can both see where this goes. Then you will have attacks right outside the front door, so we set up security a mile away. Then there are attacks there, rinse and repeat until security is fifty miles from the airport and we are still moving back to stop the attacks…
So clearly the only answer is a security checkpoint outside every house…anyone got Cheney’s email address…?
Oregano doesn’t false-trigger the schnozzes of sniffer dogs. But, if Substance X can reliably false-trigger the bomb detection apparatus, how is it not reasonable to say that a fake bomb built with Substance X allowed to pass through undetected isn’t a reasonable, if not 100% accurate, indication that the system has failed in some way?
This Substance X you speak of. What is it? I don’t think it exists.
I wasn’t thorough enough earlier. A lot of energetic materials that the average terrorist is going to be able to get his hands on are going to be in the 200 to 300 g/mol range. I only have a cursory knowledge of organics, but it seems to me that would rule out a lot of things. Also, one of the tests used is a GCMS, which, as I understand it, is pretty much impossible to fool.
Well, for one thing, medical nitroglycerine has been known to trigger certain types of explosives detection systems since it’s, y’know, an explosive.
They can be made to be pretty much impossible to fool, but the more foolproof you want the test to be, the longer it takes and the more expensive it is, especially if the list of things you want to be able to detect is very long. I don’t know how long it would take for a fully thorough test, but I suspect it would be significantly longer than most people woud be willing to wait at a checkpoint.
Any organic chemistry analysis experts out there?
…and they had half a brain on them… enough of them don’t to make the checks actually work to a reasonable degree.
How smart do you think suicide bombers are?
Since it’s, y’know, an explosive, would it be allowed on a plane? I know nothing about glyceryl trinitrate (pharmacological name, according to Wiki), but Wiki shows the molecules as identical. Do they put a binder in that prevents detonation? I’m not sure if I would consider this a false positive. I’ll concede that if this is getting through undetected, there is a problem. However, if the systems are finding it, like you say, then they’re not getting snuck through.
IIRC, those puffer systems you stand on blow air over you, catch the large organic molecules on a filter, wash the filter with a solvent, and then GCMS the solvent. the list becomes quite a bit shorter when we know that most explosives are going to be very high in nitrogen, and generally have at least one oxygen for every hydrogen, and one to two oxygens for every carbon. It doesn’t take as long when we can narrow down the list like that.
It seems that those systems take about 20 - 30 seconds. Of course, to prevent backing up the lines, they assign you to lanes ‘randomly’, creating holes in the security system (the scope of which is probably more in line with the OP than my semi-hijack). At a lot of airports, this same puffer system is employed on checked luggage as well. It is very difficult to not get residue on the outside of containers.
Yes, but what do they do in the actual GCMS process? If they just find molecular masses, then there’s going to be a lot of false positives. If they also heat the molecules to crack them, and then get the molecular masses of the fragments, too, that would tell them a lot more.
I think they do the latter, since I seem to recall a FFT being done with the data. It’s been a couple years since I’ve researched them, and I wasn’t familiar with FFTs at the time. I think I still have the journal articles on my office computer, I’ll try to dig them up tomorrow.
Well, is she coming?
We promise. As long as she stays out of the the Pit, what could possibly go wrong?