I work with test equipment on a daily basis. I do not believe that there are a large number of what we would call false positives, or the machine alarming for non-dangerous chemicals.

There may be some, and in the initial roll out of the technology there were likely many. However, what we are calling "false positives" are more than likely from one of three sources:

1. Cross-contamination from poor handling practices for the TSO's
   
2. Improper preparation or cleaning of the machine following testing of a known sample for calibration and the subsequent cross contamination
   
3. Random alarms (if they will do it for the WTMD and Scanners, they will do it for the ETD.)

I have observed the first, but I only suspect the other two and I could be wrong.

The testing process they use is very well tested in a variety of situations. It is successfully used across multiple industries and processes. However, it still requires thoughtful preparation of the sample, meticulous cleanliness and avoidance of any source of potential cross contamination. The CP is not conducive to any of these and "false positives" are inevitable. A more correct term for "false positive" would be "alarm from unknown source." That is a lot more words but is more accurate.

If I were doing this testing in industry, let's just suppose it is to check a machine before maintenance, the absolute first-before-anything-else-thing I would do is run another test while verifying that all the the testing parameters were properly done before accepting the result of the test. We would never tear down a machine for repairs based on a single test without verification. Yet that is what they do when they proceed directly to an invasive search without verifying the integrity of the sampling.

But, that testing is done by highly skilled technicians, many with specific certifications in the processes, and the cost of failure can be significant. However, at the CP, the testing is done by... er.... uh.... TSO's, and the cost is ours, not theirs..

Thank you for this very clear and erudite explanation. I wish you had been my "tester" yesterday! :)

I was too shaken in the moment to request a second "test" of my phone. It occurs to me that you are quite right re. cross-contamination. The guy certainly did not change his gloves before/after handling the various discarded test circles and then mine. And it looked like routinely there was no cleaning of the surfaces on the table, in the bins, or in the little paper slot of the machine. I can't believe I didn't think of this or notice it, considering my usual level of neurosis about such things!

What really concerns me is the TSA opinion (even expressed here on FT occasionally) that it is a "zero downside" or "low cost" solution to do the status quo.

If they're not finding actual explosives, just finding ways to violate civil rights, that seems quite inappropriate/foolish as an American policy.

As a side note, I am totally in favor of you know, actual security. I have flown El Al dozens of times, for example. It is a totally different experience. Once my DH was called aside by the El Al person to a separate room (leaving screaming jetlagged kids with me and no contact - now that was stressful) and even his follow-up interview was done incredibly respectfully etc. (It turned out that someone with his [common] name was draft-dodging, so it flagged. But his passport and answers to "what's your father's name" and verifying etc. led to a relatively quick release.)

--LG

No. It takes an incredible amount of energy (e.g. lighting strikes, high pressure at 600 degrees in the presence of a catalyst, highly specialized and evolved bacteria) to convert the nitrogen gas in the atmosphere to any useful form of nitrogen, such as nitrate, nitrite, ammonia, etc. Nitrates may be common, but they are almost universally the result of industrial chemistry used to create commercial and consumer products. (And possibly grilling protein at high temperatures ;))
Really? How? I guess you could use something like MALDI, but having done a few MALDI samples, I can pretty much guarantee it's not a feasible technology for our friends in blue at the moment. Even if there were a benchtop system that was easy-to-use, rugged, and eliminated the need for a skilled operator, it's almost inevitable that some molecules will break into sub components. Explosives, by their very nature, are not the most stable molecules. :D
Agree with everything you said, but I think there is a fundamental disconnect about the definition of a 'false positive'. I understand why golf shoes (heavy use of fertilizer on golf courses) and contact cleaning solution (hydrogen peroxide) and hand lotion (fragrance chemicals) may set off the detector, and that is technically not a 'false positive'.

However, from the perspective of airline safety, and the perspective of a passenger who was just groped, it is quite logical to consider those results to be a 'false positive', as they pose no safety threat.

I absolutely agree. The terminology is deliberately selected to make it sound like one has an explosive residue, when all that has occurred is that a chemical resembling explosive residue has been detected. The TSO's do not have the knowledge to understand the difference. If the machine generates an alarm, to them it is an explosive.

Yes, and not just "to make it sound..." but rather, the machine blinks out the message, "explosive detected" (!!!!!) That gave me quite a panic. I figure for the agents who see that all the time, they must either:
1. become inured to "explosive detected" and therefore not sufficiently on guard
or
2. view normal innocent people as highly dangerous from the first contact, and therefore become incredibly paranoid

--LG

No.

Sorry for ressurecting this old post, but seemed the closest to this question....

I recently alarmed during a pat down after opting out.

Then alarmed at enhanced pat down..... and THEN carry on bag alarmed. Ultimately cleared and flew, about 15-20 minute delay. Treated decently by the senior agents, but it was my home airport and I am flying once or twice a week from there. (One or two of them knowing me, at least a mild recognitiuon, probably helped.)

So....I have both print outs from the last two scans....

(Annoyingly, it says "explosives detected", and -as TSA Ron points out- this is false. Or may be false- the machine only detects compounds 'consistent with explosives'...whatever.)

Here the thing(s)

1. Same bag flew and screened on Sunday and Monday. On tuesday it alarmed. Only change was fresh laundry, from a home washing machine...no different soaps used.

2. NO: lotion, new soap, nitroglycern/meds, fertilizer, golf, handguns, ammo, etc, etc. Nothing at all in my personal activities profile that would explain a compound that could be confused.

3. The swipe at the enhanced screen shows a positiive for 'substance E14+'. The next swipe, same machine, different agent, of the bag shows a positive for 'substance E6+'. ...???? The spectrum print outs are different for the two. (I do not have the print out for the first swab that was on a different machine.)

I'd scan and post, but I suspect the agents could get in trouble for me having this...and the event is linked to me. Anonomizing it will reduce it to nonsenseIMO

Not much online looking into the details, E6 vs E14 nor any of the other designators they use for unique detection limits.

And I'm flying tonight..same bag, albeit washed with detergent since the trip that had this issue. I'll leave a bit of time just in case. :(

Yes, I must admit, on one of my exploits through the TSA gauntlet in unconstitutional land, the TSA found something dangerous with this stupid exercise -- my temper.

:)

BTW since this original thread, I have had a couple more similar experiences - all departing from ORD, and all with the same luggage/contents used elsewhere with no issues. I think it's the late flight I typically take, with some trainees or something on TSA.

--LG

They're false positives because the TSA treats them as an indication of explosives, and yet explosives are not present. We can argue about the way to resolve the resulting false positive "hit," but it is nonetheless a false positive the way the TSA reacts to it.


True, but they can give an overall signature rather than alarming on just components. The GC/MS machines I've used in a lab setting spit out a chart with peaks for different compounds and fragments, and the distribution of those peaks will correspond fairly well to the overall compounds present. Even back in the early 90s when I worked with that equipment, the computer attached to the GC/MS was able to analyze the overall signature and report on compounds matching the fragments detected in their proportions.

This would at least reduce the false positive rate without significantly compromising the ability to detect explosives.



And if one doesn't find anything in that search, that should be the end of it. Unfortunately, as I and others who have gone through it can attest, rather than admitting their sampling process or machine may be at fault, the TSA continues to treat the pax as a would-be terrorist, making threats, causing the pax to miss their flights, and of course bringing in LEOs for more intimidation.


Several years ago when I "broke the ETD machine" (words by a TSO to me when it alarmed on my swab, but then also on just about everything else they tested), it wasn't a big deal, because the TSO let it drop there.

I think my much more recent experience (this year) of being detained in a back room with threats of "bad things" (calling in the FBI and missing my flight) with the constant refrain of, "You've got to understand it's just the times we live in," was certainly a big deal. And this of course after a complete dumping of all my possessions and of course finding absolutely nothing... yet the TSOs were beholden to their stupid (broken) ETD as if it had to be right and everything else their investigation showed them was wrong.


Like I said above, if only it worked that simply... maybe it even does at some checkpoints.


But they all do have chemical signatures; when analyzed by ETD, there will be some ratio of each of the component parts which matches a known explosive. Yes, for improvised nitrate-based explosives, it's trickier (since you can successfully, to some degree or another, nitrate many common organic bases into an explosive compound)--but then, the ETD should be alarming on the combination of nitrates and those organic bases, not just on the bases themselves.

Also, the level of alarm should be different. Match a signature for a known explosive compound (not just the nitrates or an organic base), and one alarm goes off and requires a more detailed check. Match just the nitrate or an organic base (say, glycerol), and a lesser alarm goes off, requiring just an x-ray and possible hand search of items--not the full back room rigmarole.


I've observed the second on several occasions. One landed me in the back room grope-fest, and the TSOs couldn't understand why the ETD kept alarming. Well, duh, because you're not properly cleaning the machine! Try a different machine, with different TSOs performing the check. Once they finally did that, they let me go--but it took an hour to get them to that point.

I agree with your whole post (though didn't quote the whole thing in the name of brevity).

It's obviously a "big deal" to repeatedly violate people's civil rights. I think it's really clear that the TSA does not have the insight or funding or management to do things that would make technological, scientific, or security sense. They have to spend their limited financial and human resources on showy machines and fundamentally: slowing down travel and adding a layer of intimidation.

I doubt that the TSA was set up to do this slowing/intimidation theatre instead of security, but they're not in a huge hurry to change things, from what I can tell. It would surely be more costly to hire competent personnel, to use accurate machines, to maintain a canine fleet....

--LG

what's the point of the swab check if its not accurate (false positives)?

The piont is the same as most other security procedures - to look like you're providing security so the sheople feel safer, politicians can cover their butts and the "mah authoritee" types can be employed and feel powerful.