It was a mistake only if one is willing to reduce the idea that alarms always indicate something dangerous. ETD alarms indicate that there is a chemical present that is also present in explosives. In other words, something dangerous.

Splitting hairs serves no useful purpose, and neither makes the other right or wrong, it just makes the conversation inane when one party pretends obtuseness.


Given the number of conversations we have had on this subject I honestly cant think of a more appropriate term. I didn’t call “you” obtuse, only those who intentionally “narrow the definition of "false positive" down to its most basic form”. If this is what you have done then please feel free to apply the term to yourself, with my compliments.

Once again, for those in the cheap seats: ETD systems alarm when a chemical is detected that warrants further investigation by the screening TSO. That does not make the alarm a “false alarm”, it makes it an alarm. One that must be investigated further.

It was a mistake only if one is willing to reduce the idea that alarms always indicate something dangerous. ETD alarms indicate that there is a chemical present that is also present in some explosives. In other words, something dangerous.

Splitting hairs serves no useful purpose, and neither makes the other right or wrong, it just makes the conversation inane when one party pretends obtuseness.


Given the number of conversations we have had on this subject I honestly cant think of a more appropriate term. I didn’t call “you” obtuse, only those who intentionally “narrow the definition of "false positive" down to its most basic form”. If this is what you have done then please feel free to apply the term to yourself, with my compliments.

Once again, for those in the cheap seats: ETD systems alarm when a chemical is detected that warrants further investigation by the screening TSO. That does not make the alarm a “false alarm”, it makes it an alarm. One that must be investigated further.

Many of the chemicals the ETD systems detect have civilian uses other than to make explosives. Their presence in someone’s baggage is not really all that uncommon, but it does require a response from TSA. Maybe that is where you are having your issues, you are having difficulty telling the difference between an ETD alarm and a “false positive”.

I don’t have that issue, so now you have a riddle to solve. Glad I could help you.

"further investigation" meaning you get your testicles rubbed by a TSA clerk in the private room. For having used hand soap.

You are being a stickler for semantic purity without gaining anything from it. Some of us have used the term "bad results" yielded by poor testing methods. Regardless, if a test alarms on commonly used products, it is for all intents and purposes a false alarm or false positive and the shorthand is useful. If the methods used are sensitive to compounds used in explosives but also used in a wide variety of products, the test cannot reasonably be used to justify TSA's genital and anal massages of innocent passengers in the private rooms. After two years, you have all these alarms leading to no discoveries of explosives: it is probably a clue for you folks to try something different.


Like hand soap, shampoo, or any of the other household items that contain these chemicals. After two years, that's all you've found. What exactly is dangerous about these? Oh, they could be used in a bomb...

Only if you accept that since terrorists both reason and breathe, all reasoning and breathing beings should have their privates investigated. That's the kind of test you have. One too broad to be either useful or decently used on innocent human beings.

We are fortunate that our TSA clerks have the education and work background in chemistry and test methodology to set us all straight.

Ron, you've crystallized the entire problem with TSA screening. To the TSA, something can be "dangerous" even though it poses no threat.

As an aside, you should ask your local supermarket to put the hand lotion behind the counter. Your training teaches you that it is "dangerous"!

It is not so much that the testing method is useless than it is the inappropriate application of the technology. Furthermore, the method of resolution is highly inappropriate for the nature of the alarm.

Since everyone is a suspected terrorist, the TSA must have some method to weed out people that do not need further checks. They pretend that the ETD is to find problems. What they are looking for are people that need no further check as they do not "trip" the alarm. The ETD used as an indicator of innocence by the lack of an alarm is correct almost 100% of the time.

I believe the point being made, as well as the request for data, is to help determine whether the testing is effective or not. If the testing is effective at finding WEI, then people would likely be less resistant to it. As of now, the amount of WEI found through this testing appears to be negligible based on what has been reported to date.

I am personally of the opinion that any WEI found to date via this method actually falls within or below the actual margin of error and that searching people at random would likely give as good a result - and at a significant cost savings.

Ron: I don't know if you have access to any, or all, of the data, but with what you do know (or can observe in your position) and since the purpose is to find WEI:

1. Take the amount of actual WEI found by this method and divide it by the number of passengers where the machine has alarmed and multiply by 100 for a percentage. (Effective percentage of postive test results.)
2. Take the amount of actual WEI found by this method and divide it by the total passengers tested and multiply by 100 for a percentage. (Percentage of true positive test results.)
3. Take the total direct costs of testing (equipment, swabs, personnel, etc.) and divide that by the number of actual WEI found by this method. (Average direct cost per true positive test result.)

My guesses are that 1 is small, 2 is very small, and that 3 is significantly large, especially when reviewed against 1 and 2.

My point? The cost / benefit ratios would not appear to point to this an effective test method for finding WEI - a primary goal of the administrative searches by TSA.

As all of life comes with risks, the struggle is to learn how to balance those risks against the costs and rewards. Sometimes it works out that the costs involved (ETD testing) exceed the reward (finding WEI via ETD testing) for the limited risk that is present (number of WEI found via ETD testing). The sad part is, the same could be said for the (in)effectiveness of the AIT scanners.

...and that the inappropriate idiots performing the useless tests are useless.

TSA claims that they screen about 1.8 million travelers each day. I have no idea how many of those are screened with ETD but given that TSA cannot claim to have ever identified or deterred a terrorist the percentage of dangerous items found by ETD is infinitesimally small.

You misread the quoted text. I believe he was saying that explosives were dangerous, not the detected chemicals.

Splitting hairs indeed serves no useful purpose, but if there's a discussion involving a term and the people in the discussion don't agree on the meaning of the term, it's hard to have communication.

I do understand your definition of "false positive", but realize that the "E" in ETD stands for "explosive". So an equally possible definition is that a "false positive" means that no explosives were found.

TSORon, I love how you contradict yourself within a single posting:

You use two different definitions of an "ETD alarm" in use here. They differ significantly. Which would you like to use?

What he said was this:
"ETD alarms indicate that there is a chemical present that is also present in explosives. In other words, something dangerous."

I don't think I misread that at all. Read in isolation, you may have one of two possible interpretations. Read in the context of the thread, he's saying the chemicals are dangerous. Recall that ha started the banter by saying that ETD systems are particularly good at identifying something dangerous, and now he apparently wants to justify the statement by saying that because an ETD identifies chemicals present in explosives, it identifies something dangerous.

But the fact that we read the text differently does highlight his lack of clarity.

#3 would be an imaginary number, since Ronnie would be dividing by zero. ;)

The problem with methodologies like that is that it ignores the deterrent effect, which is actually, in my opinion, the primary purpose of all checkpoint security.

aaand we will never know how many sociopathic raging psycho terrorists masterminding horrible and terrible mayhem upon us have suddenly come to their senses due to this invaluable deterrence factor which brings us back to the point that no point is needed for any of these exercises at all. :eek:

So why haven't all of these terrorists chosen softer targets?

It's not like there's a shortage of targets that would obtain even higher moral outrage than blowing up a plane, or a checkpoint line.