Paramedic Stopped at Airport Security for Nitroglycerine Residue

At least we know those chemical-residue detectors are working:

The punch line is that my bag tested positive for nitroglycerine residue. Which is, in hindsight, totally not unexpected, since it has been home to several bottles of nitro spray that at one point or another have found their way into my pockets and then into my bag. (Don't look at me like that -- I'm not stealing the damn drug. It's just that it's frequently easier to shove them in a pants pocket rather than keep fishing for one at the bedside or whatever, and besides, we've now gone to single-patient use sprays so that once you use one on one patient, it's fininshed.) Whether one discharged, or leaked, or whatevered in my bag, it somehow got NTG molecules all over the place, and that's what the detector picked up. The guy said this happens all the time but I'm not so sure, and in any event I'm not even remotely certain how I could go about getting the NTG residue off my bag so this doesn't happen in the future. NTG spray has a pretty distinctive smell. All I can smell in my bag is consumer electronics, so it must have been some minute amount somewhere.

Posted on October 25, 2006 at 8:59 AM • 44 Comments


KeithOctober 25, 2006 9:16 AM

If this happens "all the time", there's obviously the risk that the security guards, as the one in this story seems to, get relaxed about it. Too many false positives, etc, etc.

RoyOctober 25, 2006 9:51 AM

Modern smokeless powder (what replaced oldfashioned 'gunpowder' of yesteryear) is either single-based (nitrocellulose) or double-based (nitrocellulose and nitroglycerin). All the rifle and pistol ammunition carried by security people contain one or both of these chemicals, yet the airport detectors are unaware of their presence. Why? Because cartridges are sealed with a good friction fit or a thin film of lacquer, so that no nitrogenated molecules escape in a density thick enough to trigger detection.

The fact that the gadget detected nitroglycerin where it was exposed to the air is not surprising. That the gadget fails to detect all the huge number of true positives moving around the airport should be disturbing.

The only difference between the paramedic's bag and a dynamite bomb that would entirely escape detection is that the bag wasn't sealed with a thin film of lacquer.

D-CafOctober 25, 2006 9:56 AM

Well, based on the rest of his story and what he went through (more extensive screening, paper work, interview, etc), I don't know if we can be to worried about the false positive to often affect. I would actually say this account is one of the few times the screening actually worked.

I would say more of the problem is that since the nitro checks are random, there is still probably only like a 1% chance (or less) of someone actually carring a bomb getting caught. Is that random chance enough of a deterent? Doubtfull. Be better if they could do an analysys on every bag that goes through the screener (air sniffer in the xray machine?). I don't know of the limits of the technology, so I'm assuming that's just not technically feasable yet.

LordRichOctober 25, 2006 9:57 AM

They claimed "this happens all the time" when a drugs sniffer dog showed interest in me. They still spent ages questioning and searching me though, so it's not true that they will always become more relaxed when there's lots of false-positives.

D-CafOctober 25, 2006 9:59 AM

Oh, and of course you are trying to detect the actual bomb itself, but the residue left on other things that may have come into contact in the preperation of the bomb or bomb placement. Seal the bomb up in a plastic bag, but did some of it's molecules rub off on the outside seal of the bag as you were placing it in? You can always be super careful, but there is a chance you will miss some form of residual contact (shirt, gloves, hand, all chains of point of contact..)

scottOctober 25, 2006 10:06 AM

Avoiding carry-over is pretty standard - one person does the orginal prep, another seals that up, a third moves that to a different location and does a secondary sealing, last person comes along with the carry-on and puts the double seal into that.

Works better if someone has made some nitrated aromatics and nitro esters from several common ingredients, and has left small puddles of that around the airport entrances and parking areas, giving hundreds of positives over the last few days.

Joe BuckOctober 25, 2006 10:39 AM

A few years ago, my toddler's car seat set off the explosive detectors at an airport. Her diaper had leaked a bit, and apparently the nitrates in her urine were enough. But the security guy said he'd seen this repeatedly.

Fred POctober 25, 2006 10:47 AM

"in any event I'm not even remotely certain how I could go about getting the NTG residue off my bag so this doesn't happen in the future"

Wash the bag. Well, and repeatedly. Say, around 3 washings with soapy water and 6 with water will likely get it down to an undetectable level.

merkelcellOctober 25, 2006 10:54 AM

TSA should have a heart attack and not have access to nitro spray. How many of us have used this to deal with heart conditions?

jbOctober 25, 2006 11:02 AM

"This happens all the time" is just to calm down the suspect. If someone gets more nervous after that, it's likely they're carrying some kind of contraband.

AnonymousOctober 25, 2006 11:09 AM

A few years back, pre-911, going through an airport in Canada I was stopped because they found gun powder residue on the backpack I was carrying. This didn't surprise me because I had recently been on a rifle range with that bag. They questioned me for a couple of minutes and I showed them my military ID and they let me through without to much fuss. I wonder what would happen if I tried that now.

mpdOctober 25, 2006 11:23 AM

@ Craig Hughes

A false-positive in this case is if the machine detects nitroglycerine where there isn't any. The author admits that nitro-spray has been in the bag.

antibozoOctober 25, 2006 11:32 AM

This may be apocryphal, but from what I've heard, what happens all the time is a false positive due to residue of glycerine-based products (hand lotions and the like), which are numerous.

AlanOctober 25, 2006 11:52 AM

Sounds like you could make some interesting mischief with this. Have a boss that travels a lot? Leaves his luggage around while going to meetings? Spray a bit of miracle grow on his bags and maybe he won't come back.

MikeOctober 25, 2006 12:01 PM

This happened to my brother-in-law at St. John's airport in Newfoundland. The day before he had been visiting an aged Uncle "in the home" and had handed him is bottle of nitro tablets.

I see a new movie plot terrorist threat - a real terrorist is dressed as an ambulance driver and pretends that he has a been with a patient with a heart condition (better yet have an accomplice fake an angina attack in the security line forcing the "ambulance driver" to give him his nitro for all, including the security guards to see) gets on board with real explosives. Hilarity ensues.

Aw crap, I shouldn't have said that with the Bush Administration listening...

SteveOctober 25, 2006 12:09 PM

In November 2001, I was randomly selected for chemical sniffing at London Gatwick. The BAA employee said that false positives from medication weren't uncommon. She also said that official procedure if the alarm sounded was for a bunch of guys with guns to run up behind me and try to look like they were in control of the situation.

So this report doesn't surprise me at all. I'd expect that quite a lot of people with heart trouble have had similar experiences.

@mpd: from the point of view of the design specification of this particular machine, maybe it's not a false positive (since the machine was designed to detect nitroglycerine, not bombs).

Considering the security system, it certainly is a false positive, because an alarm has sounded when there was no threat. If we could somehow design the machine to tell the difference between traces of medicine, and nitroglycerine in explosive quantities (that is, test for bombs, rather than testing for nitro), then we would. Unfortunately that is not currently possible, so all such systems will generate false positives from trace residues.

JPeOctober 25, 2006 12:14 PM

Few years back, around 2003, I used to work as instructor at military base. At same time, I made some extra hours at place where they were using ITMS "sniffer"
At one excercise, where I was building up some explosive fields out of TNT (to simulate artillery strike) I used my civvy bag to haul about 40 pounds of TNT... Next day, ITMS dind't give alarm out of the bag neither my car I was using during that excercise...

Ed T.October 25, 2006 12:49 PM

"...official procedure if the alarm sounded was for a bunch of guys with guns to run up behind me and try to look like they were in control of the situation.

So this report doesn't surprise me at all. I'd expect that quite a lot of people with heart trouble have had similar experiences."

If a bunch of guys with guns run up behind someone with heart trouble, we might have a totally different type of incident to deal with!


RoyOctober 25, 2006 1:26 PM

Does anyone know how specific the detector is? What functional groups would set off the thing?

JROctober 25, 2006 1:50 PM


My brother is a big hunting and shooting buff, now involved with big game ranching in Texas. He was also an IT executive for Compaq, and as such flew all over the world on business.

He would have his carry-on wiped down, and the machine would register postivie for "explosives" (read gunpowder and residues) and then it would be searched very closely.

Usually, the security folks would then apologize for the false positive, at which point he would explain that it wasn't a false positive at all, but that dove season (or whatever) had just started, and that they were going to get a lot of hits, as well-to-do buisnessmen hunters would be flying in and out on their hunting trips.

They were never quite sure how to react when he said "It isn't a false positive at all..."

JasonOctober 25, 2006 2:52 PM

Do you think it's more likely that it actually 'happens all the time', or that the security folks have been trained to put a suspect at ease by -lying- about the incidence of false positives, in order to discourage a guilty person from doing anything crazy?

ThomasOctober 25, 2006 3:07 PM


"""A false-positive in this case is if the machine detects nitroglycerine where there isn't any. The author admits that nitro-spray has been in the bag."""

The _machine_ worked, it detected NTG, just like it was supposed to do.

The _system_ failed, it false-flagged someone.

A certain false-positive rate must be expected in any system, so a single failure does not mean that the whole system failed.

The question is whether or not this system the best we can do for the cost (money/convenience/liberty).

the other GregOctober 25, 2006 5:48 PM

"The question is whether or not this system the best we can do for the cost..."

And the question before that is, what is the system supposed to do?

Craig HughesOctober 25, 2006 7:08 PM

@ mpd & Steve:

"The guy said this happens all the time", and I bet approximately 0 of those times have been actual terrorists. So the machine is very likely acting to distract security inspectors' time and attention away from terrorists and onto innocent paramedics & heart patients.

True, the machine may have yielded a true-positive in testing for substance X, but the system failed, generating a false-positive in testing for terrorists.

Jon SowdenOctober 25, 2006 8:34 PM

Craig Hughes:
"The guy said this happens all the time", and I bet approximately 0 of those times have been actual terrorists. So the machine is very likely acting to distract security inspectors' time and attention away from terrorists and onto innocent paramedics & heart patients.
Your assumption is that there are any terrorists about for the security inspectors to catch ;)

iwormsOctober 26, 2006 12:17 AM

I asked what was going to happen to the form. "Oh, nothing,"

Why fill out a form that is of no use? Either he's lying or his boss's boss is stupid. Equally bad.

AnonymousOctober 26, 2006 1:54 AM

I work in a lab; this happens to me too. They take it very seriously, and look very hard for real explosives.

But this is not a *false positive* - it's the definition of a screening procedure. Screening procedures are sensitive - tuned to not give false negatives. Then you follow up with an investigation procedure tuned to not give false positives.

Medical diagnostics has worked this way for decades; a fair percent of GDP is spent on this stuff, the maths is well understood.

and....action!October 26, 2006 3:03 AM

Enter, stage left, mad mullahs bent on destruction sporting white coats and stethoscopes

another_bruceOctober 26, 2006 3:49 AM

the paramedic was overly deferential to the security corps. fill out a form? kiss my big, fuzzy ass!
he could only smell consumer electronics in his bag? **sniffs own bag**. somebody packed a lid of sticky bud in here recently!

SteveOctober 26, 2006 4:31 AM


"this is not a *false positive* - it's the definition of a screening procedure. Screening procedures are sensitive - tuned to not give false negatives."

In other words, this *is* a false positive of the screening procedure, which the secondary check reversed, because it's designed to expect and handle false positives. They're still false positives - they can be handled, but they aren't desirable.

If this is "not a false positive", then what would you say if the guy was arrested, convicted of terrorism, and then the conviction overturned on appeal. Is that then "not a false positive", just because one of the checks somewhere up the chain corrected it? No, it's a false positive of some parts of the system, dealt with by another part which expects false positives.

Normally I'd say that the semantics aren't important, but on this occasion the machine's result incurred an additional cost of dealing with a passenger. What's the benefit (other than to government PR, or the PR of the company which builds the machine) of saying that it doesn't count as a false positive?

Dr. HazmatOctober 26, 2006 5:15 AM

I’m the guy this happened to. Reading some of the comments here, I feel that I need to clarify and/or extend my previous remarks…

First of all, please understand that my post was not intended as a commentary on air travel security. I have a personal habit of having horrible things happen to me when I travel, and posted the story to my LiveJournal mostly as a means to amuse my friends; the tone of voice behind the story is one of weary resignation, not frustration or anger. (Though I’ll note that had I known Bruce would repost it here, I might have been more eloquent and thoughtful.)

Second, as mpd and the anonymous poster above me have noted, this was not a false positive result. The detector correctly detected (and identified) the nitroglycerine residue on my bag, and it functioned exactly as expected. The screening personnel also functioned exactly as expected: They investigated the source of the alarm, asked me reasonable questions to determine why the alarm condition occurred, and, having been satisfied that I did not represent a threat to air safety, allowed me to board my flight. The alarm condition was thus valid (I had nitroglycerine molecules on me), but irrelevant to the overall goal of preserving the safety of the flying public (I’m not a terrorist, so who cares if I have nitroglycerine residue on me?).

Third, keep in mind this was at a Canadian airport. CATSA isn't a whole lot better than the TSA, but it is marginally less stupid, and the margin seems to make a difference.

The anonymous poster's comments regarding medical diagnostics are particularly astute and I think the comparisons are very valid: If you spot a suspicious lump on ultrasound, you naturally biopsy it. When the biopsy comes back benign, we don't turn around and say the ultrasound was a waste of time -- we say that the diagnostic process worked more or less as expected.

For a variety of reasons, though, it feels as though there was some kind of failure here, although it's difficult to figure out exactly where the failure occurred and what should have been done differently. It's tough to argue that we shouldn't be checking for explosives, it's tough to argue that we shouldn't additionally screen people found to have explosive residues on their personal effects, and it's tough to say that we shouldn't document instances where residues were found but posed no threat. It may be that we need to take situations like this in stride and recognize that they will happen, and design the system in such a way that these situations do not escalate into something bigger than they need to be. Viewed in that light, I think The System worked fairly well overall (though I would have preferred that it worked on someone else).

My biggest concern about the whole incident is what happens to the report that was filed as a result of the positive explosives test; not being one to have much faith in the government, I’m not at all convinced that “nothing��? is going to happen to the document. Insofar as there are other risks here, I think the biggest one is the personal shock that may come from being suddenly yanked out of line and subjected to a more intensive screening process.

As to some specific comments...

Thomas: "The question is whether or not this system the best we can do for the cost (money/convenience/liberty)." I agree. After having had about a week to think about it, I've come to the tough-to-swallow conclusion that it is the best we can do for the relative costs. The whole thing seems excessive but on further reflection, as I said, it's tough to argue against any one aspect of it. It pains my libertarian soul to say this, but this may be about as good as we're going to get.

One final risk comes to mind: Because this event was related to airport security, and because we're used to thinking of airport security as being mostly useless, we run the risk of writing off those procedures which actually do result in a net increase in safety to the traveling public.

SkipOctober 26, 2006 7:23 AM

This happened to my sister in law as well. She works in a cardio unit in a Hospital. Had enough traces of nitro on her purse to set the detectors off.

solinymOctober 26, 2006 4:40 PM

I don't have exact details, nor would I post them, but I've seen sensors that detect the major categories of explosive residue; I recall seeing labels on one for dynamite, TNT, RDX, PETN, HMX, Semtex, etc.

Most explosives have a nitrate in them, as an oxidizer. I wouldn't be surprised if some less-expensive sensors just checked for those.

DougCOctober 26, 2006 7:31 PM

@Dr Hazmat,
Nitroglycerin is soluble in alchohol (just about any common kind), acetone, etc, and probably will wash off OK with soap. It also has a decent vapor pressure at reasonably elevated temps, so just leaving the thing in the sun should do it.

Were I designing an explosives detector for the popular (stolen military) terrorist explosives, I'd sure be looking for nitrates/nitrites and other decomposition products. Good place to start, most anything you didn't manufacture yourself would be caught in that test.

Were I designing a real one that I cared about, that would only be the start. There's lots of ways to make something go bang that don't use any nitrates at all...

Anyone who has read Tenny Davis book "Chemistry of powder and explosives" will have found quite a number of alternatives that are currently unchecked for.

In normal commercial use, explosives are literally all about "bang per buck". The nitrate ones tend to be best tradeoff there, so are popular. The military adds a requirement that they not go off when hit by a bullet, for reasons that ought to be obvious, so they use things like TNT, RDX and so on. They don't use PETN in bulk as it will go off when struck hard -- it's used only in detacord.

Some WWII (and I) history shows that as countries are stressed by wartime shortages, they turn to other things than nitrates, because they still have them at all - cost becomes less of an issue than not losing the war. We are currently lucky these are all gone except for custom manufacture, as some are quite hard to detect, or detecting them would give huge numbers of false positives.

PyersOctober 27, 2006 4:41 AM

Not surprised a medic (of some form) would have glyceryl tinitrate (that is what nitroglycerine is called when used by the quack industry) What does surprise me is that is was detected. Pharmacological doses of GTN are in the milligram (or even microgram - sprays deliver 200ug whereas tabets give about 500ug) quantity ......

PS As a BTer welcome aboard!

Max HyreNovember 15, 2006 5:00 PM

Why bother with the form, or anything else? Why should being a paramedic make a difference? Why even care what his name is? Once you've searched the person and verified he has no explosives, you've done your job---no plane go `boom'.

The only non-theatrical purpose I can imagine is to check for terrorist connections, and given the number of non-bomb-carrying people detected, we know how effective that will be.

AlDecember 13, 2006 4:33 PM

I'm a doctor and my partner is a nurse. We are about to fly in to London soon and then around to 5 other european countries...
With the recent scares in the UK this should make for an interesting trip. As we cover the high dependency ward and have LOTS of patients with GTN infusions, patches, sprays, etc...

To the person who described this as a screening test you are exactly right. This is designed not to miss false negatives ie high sensitivity. The flagged cases are then further investigated as a screening test does not need to have high specificity to be useful.

It's also worth noting that GTN preparations like Rectogesic cream are used to relax the internal anal sphincter and facilitate healing in patients with anal fissures or sometimes after haemorrhoid surgery... thus these patients and family/contacts or general surgical nursing staff may also be 'contaminated' with residue.

AlDecember 13, 2006 4:51 PM

EDIT: though hopefully this last group of patients wouldn't have to sit for long periods of time in economy!

Just had another thought... one of the ppl mentioned here that _nitrites_ are tested for as well as nitrates... when someone has a possible urinary tract infection we do a ward screening test (dip stick) on their urine looking for leukocyte esterase (product of white blood/immune cell metabolism) and NITRITES (product of bacterial metabolism).
Some1 I think mentioned their babies nappy earlier... I wonder how many little old ladies with bladder infections would be picked up... (probably not usually a target of the 'randon' screening process tho..)
just a thought... And yeah, running at some old guy with a heart condition carrying guns could indeed get interesting ;)

namahaFebruary 7, 2007 7:28 PM

I had an episode at an airport recently where a bottle I was carrying that contained a homeopathic remedy tested positive for nitroglycerine. I have absolutely no idea how this could have occurred. They brought out the bomb-sniffing dog, filled out an incident form -- whole shebang. There were several other bottles in the bag. I begged them to let me have the one bottle as it contained a remedy for Lyme disease, which is critical for me to continue taking. They tested the bottles again and this time the original one turned up negative, but two others tested positive. The guy doing the testing speculated that it was because the substance rubbed off through THEIR handling of it. They confiscated the two bottles regardless. I would love to know how to understand all this, and how any of my belongings could have come in contact with nitro. I am not a medical person and do not own or use weapons of any sort.

medic1July 16, 2007 4:34 PM

I'm a Paramedic instructor. I often have to travel for work purposes. One of the topics I teach in the program is pharmacology. I always put the pharmaceuticals, including nitro spray, in checked luggage. I've never been questioned or checked.

Obviously, pharmaceutics and needles for giving injections are not in my carry on luggage.

Sparky SantosDecember 23, 2008 12:40 AM

A month after 9/11 while heading back from Japan, I had my bag opened to reveal 12 Japanese 12-inch GI-Joe type dolls. The baggage guys told me they thought I was carrying a suitcase full of plastique. They were happy to be wrong.

AltairDecember 29, 2009 11:02 PM

Was stopped in 2004 in FL and carry on swabbed ?ion mobility spectrometer? IIRC the machine was by Perkin Elmer. The trigger seemed to be a home remedy by my GF for a skin rash, mainly petrolatum skin lotion ("Bag Balm") plus powdered sulfur. No nitration to my knowledge.

I explained and yielded the home remedy, carried in a zip-loc bag, after numerous cleaning wipes and swabs they let me keep a cell phone charger and some data cables that were also contaminated.

Fortunately I had allowed plenty of road time for traffic and did not miss my flight. I did offer to pack my GF's bags for her next trip ;-)

The "social contract" question is stated here as well as anywhere on the www, I dont have all the answers but personally base from the US Constitution.

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