Explosives Detection in Security – How it Works, and Decoding “Alarm Resolution”

If you’ve been unlucky enough to have the TSA, for example, “sample” or “swab” your hands for one of their explosives detection tests, and that thing set off some kind of alarm, you’re probably familiar with the hassle that can entail. If you haven’t been through that ordeal, count yourself lucky. You should still read on, because we’re going to tell you what those alarms actually mean, and how they’re usually “resolved”. Why? Because the TSA, amongst others, keep saying that explosives trace detection (ETD) and alarm resolution in explosives detection systems is “SSI” – Sensitive Security Information – and we know that it really isn’t. So here we go.

TSA Attitude to “Explosives Trace Detection”

The TSA’s SOP states that “passengers and other unauthorized individuals must not be allowed to view EDS or ETD monitors and screens” (Screening Management SOP, 2008). The same SOP states that those screens must not be photographed either, of course.

Alarm resolution and procedures is still considered SSI, as well as the two little nuggets we just told you. However, the information is freely available to those who have the means and methods to look for it – and as it happens, we do. That’s why we’ve got no qualms in retelling it to you.

Explosives Detection Systems – What?

Swab and handling tool

Explosives detection really comes in three forms – you can either have a dog sniff around bags and people, have bags go through an “EDS” machine (which stands for Explosives Detection System) that uses x-ray imaging, or you can have machine “sniffers”, which are in use both in airports, public high risk buildings and emabssies, for example. We’re going to focus on the last one, since we all know how dogs work, and the EDS machines are basically x-ray machines with a computer programmed to look for the densities and patterns correlating to a bomb or chunk of explosives. We’ve covered x-ray machines and the likes here and here and here.

So. “Sniffers” are those pesky little machines that eat little strips of paper or teflon and tell the operator if there are traces of explosives on them. Simple enough, really, as long as we don’t get too technical. There are a few “buts” in there, and we’ll get to those. First of all, we’ll let you in on how the sniffers basically work and why the TSA and other security agencies and companies like to use them.

Sniffers can analyse samples relatively quickly, they’re easier to maintain and keep than live animals, and they can be calibrated to detect either a wide range of materials, or a very narrow range. Also, they speak our language, in most cases, so they’re easier to “interrogate” than a dog, for example. Also, anyone can use them after an hour or two of training – unlike dog handling, which takes a lifetime to learn. Some say. Unless your name is Cesar Millan. Then it’s easy.

Sniffers – How?

Sniffers like this one can detect a variety of substances, and can even be calibrated to detect narcotics. In the case of the TSA, the sniffers are supposed to detect explosives only, since their mandate is to look for weapons and prohibited items, not narcotics, but who knows what they’ve set their sniffers to detect… They’re exceedingly simple to use, simply because one has to be able to train large groups of operators in as little time as possible, without a lot of misinterpretation and human errors. That means that anyone can learn to use them, with an hour or so of training and theory. To be blunt, you’ll probably be able to use one after reading through this page.

The process is simple:

– A sample (“swab”) is taken from a surface using whatever media the machine accepts. Any surface – skin, paper, metal, plastic, cloth, etc.
– The sample goes into the machine, which will use Ion-mobility Spectrometry (IMS) to analyse whatever is on the sample.
– Results are available almost instantly, with a more or less detailed analysis of what’s been detected on the sample.
– Results are interpreted by the operator, which can then determine the correct course of action.

Usually, an operator has to don gloves or use some kind of tool to handle the swabs, since they may in other cases be contaminated by the operator himself/herself.

To give things a little perspective; in 2006, more than 10,000 IMS machines were in use for security purposes only. That means military, law enforcement and security agencies like the TSA. The number is worldwide. The number has not decreased since then – exactly the opposite.

Sniffer / ETD Alarms – What and Why?

Sniffers are nice tools for security. We’re not joking – they’re very useful and they do serve a definite purpose both in checkpoint security (like airport checkpoints) and cargo security. Portable sniffersare in use both with port security,

Portable ETD

cargo companies like UPS and FedEx, and with customs agencies looking for contraband. Some of them have attachments that can “poke” into openings or under lids, to sniff out what’s inside. So what makes them go off?

Explosives. That’s the short answer. However, there’s a problem – and this is what will get you, even if you’ve never seen a speck of explosives dust anywhere near you.

The most common substance detected that will set off an alarm is glycerine. Sounds ominous, doesn’t it? Well… it is, and it isn’t. Glycerine is such a common substance that it’s safe to say that every person living in a modern society has come into contact with it, and most do on a regular basis. Glycerine is used in skin products such as moisturizers and a lot of hand sanitizers, for example, since glycerine is what will “rehydrate” your skin and make it feel all nice and soft. It’s also a part of explosives, in the form of nitryglycerine. That stuff goes boom, as Bob Burns of the TSA Blog would have put it. Glycerine on its own is an extremely safe substance.

Another one is potassium nitrate, or salpetre, which is used both in gunpowder and fertilizer – but it’s also a food additive. So there you go. Another alarm. From handling food.

It’s hard to eliminate false positives in sniffers. Actually, there are a lot of substances that are part of explosives that can be found in perfectly safe, perfectly ordinary things such as food, even. That’s why security usually treat alarms on such machines relatively relaxed – the machine will also tell the operator what substance it has detected, and that will, of course, have some impact on how the alarm is treated. If the machine specifies a single, unmistakable explosive, that warrants a more radical course of action, of course.

Explosives detected:

Most of the “sniffers” have a long list of substances that they can detect, and they can be calibrated to several categories. here’s a few of the explosives the sniffers detect:

– RDX
– PETN
– TNT (Tri Nitro Toluene)
– Semtex
– Tetryl
– Nitroglycerine (NG)
– Nitrates
– HMX
– ANFO
Dynamite and C-4 etc. are actually trademark names, and fall under one or more of those categories.

Alarm Resolution?

Alarm resolution is TSA-speak for “finding out what made the thingy go beep”, and that’s what they think constitutes “SSI”. Unfortunately, the TSA isn’t too familiar with the concept of scaling response to the actual threat, and will often go a bit overboard in their efforts to find out. That shouldn’t worry you too much, however. “Alarm resolution” means going through your bags and pockets – nothing more, nothing less.

The best tip we can give you is to clean your hands with alcohol before entering the checkpoint. A brand without glycerine, that is. Unfortunately, that won’t be sufficient for bags, clothes, etc, so if they find traces on those, you’ll just have to endure their rifling through your things for a while.

Questions, comments? Use the comment field down below, or send us an email! We read all comments, and we answer all security related questions. We’re nice like that.

25 thoughts on “Explosives Detection in Security – How it Works, and Decoding “Alarm Resolution”

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  2. I had a very bad experience at London’s Heathrow Airport on 24 April 2015 Terminal 3 at 19:15 when there was a false activation at the security screening by the Ionosphere EDS. It was later found to be a False activation by Harry Singh the senior security officer. Bunch of MORONS AND IMBECILES!!!

  3. We are looking to purchase Explosives Trace Detection Machines Qty 3. We can provide a detailed specs once we establish an initial contact with your sales team.

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  4. Does anyone know what chemicals are present in the swab? Could it contain an arscenic or cancer causing agents after all it is a chemical nonetheless and those handling it wear gloves to protect themselves.

    1. Those handling it wear gloves so as to not contaminate the sample, not because of chemicals on the swab. Most swabs used for explosives detection contain no chemicals, which is logical if you think about it for a few seconds. Chemicals would contaminate the samples.

      1. My hands have been swabbed on several different occasion and each time with in 5 minutes my hands feel like they are on fire and turn bright red. I asked the TEA agents what the swabs are made of but they will not say. They worst was on 12/10/15 at LAX when my hands were rudely grabbed by an older TSA woman and swabbed nothing traced then went through the metal detection screen which flagged my studs on my shirt so I was patted down and my hands were already bright red and burning at this time but the agent claimed I HAD TO have my hands swabbed again then another agent came up holding my belongings and said she had to check my computer and proceeded to swab my computer. I obviously have an allergy to the swab! My hands are still itching after washing them well three times and two hours later. What is the swab made of?

        1. I am fortunate to have found your response, because the same thing just happened to me last week and my husband is witness to this! We were leaving from Las Vegas and the silver threads in the top I wore triggered a “pat down” & my hands were swabbed. Within 5 minutes my hands felt like they were on fire, red, and the veins on the backs of my hands were bulging! I wetted them down, then used hand sanitizer I had in my purse and it took about 10 minutes for the reaction to subside but there is still a very rough dry spot on my right knuckles! I am in the process of investigating this–I want to find out how common this reaction is!

  5. I had a similar scare with Explosive Detection scanners at Heathrow T5 and Nairobi airport. I was carrying my Godox RS-600 Lithium-Ion rated at 102.8 w/h on my way through Heathrow T5 security, I was asked if this my property, they swabbed it and carried out an analysis, the security lady said I was lucky that the reading was just below no go category, and so I asked what did the unit detect? explosives came the reply.
    My way back through Kenya security same type of Explosive Detection scanner read very high no go category for explosive and so ensued a long delay until just before a/c door closed, the security chief cleared me through.
    I’m assuming this will happen everywhere I fly to and a good change one day I might just have to leave the Li-ion battery section behind.

  6. I find this so ineffective and a purposeless cause of grief. If an every day substance can set this “sniffer” off and it seems as though different airports have their machines calibrated differently, what is the point?

    There needs to be an industry standard first off and second, there needs to be a higher level of intelligence and decency on the TSA side. My wife and I have been traveling a lot this year and has had her hand “swabbed” a good number of times and until now was not even looked at twice. This time she was strip searched both going to and coming from our destination. The appalling part is, it doesn’t take a genius to know, that having a common ingredient present does not mean said person was handling explosives. It takes more than one ingredient to make a bomb and lastly if these explosive ingredients are not found on any of the belongings that pretty much negates the threat of that person bringing a bomb with them.

    Lets be smart people who are trying to keep airports “safe”, check the belongings in new and with cutting edge technology and stop harassing the good people who are responsible for the success of the airports. Besides, we all know terrorists are smarter that the average airport security lackey any way.

  7. When this happened to me I actually was given the “Explosives Detected” read-out on a little piece of paper, with all the results. Was that a mistake?

  8. I don’t even know where to begin with my travel experience with TSA.
    It started about a year and a half ago. I walked through the xray machine, and I immediately was pulled to the side by TSA, patted down, then the big black wand came out and traced my body all over. Then I was asked to walk through a different machine that blew air around me. I exit that machine, and I was asked again to step aside and raise my arms. At this point, I am thinking, don’t these people have anything else to do then to bother a little 105 pound, female who by no means can take down the TSA or a plain. After I was hand pat down a second time by female TSA agent I was let go. On my way home from same trip in RSW airport, I walked thru the xray and immediately again, I was asked to step to side, I just happened to look back and I seen on a monitor that my arms and wrist were circled in red. The man pulled out this skinny wand and swiped my hands, then kindly said your all set. Mmm? I thought. What were the red circles, but I didn’t dare ask him that out loud. Now I travel about 4 to 5 times a year. EVERYTIME I walk into the xray, iam asked to step aside for a hand swip. I no longer wear hand lotion, hand sanitizer, or anything prior to my trips and I make sure to wash my hands prior to leaving for the airport. Why does this contiusiously happen to me? I just don’t understand. Any other suggestions or ideas as to why? Please help the constant woman of the hand test.

  9. I’m a chemistry teacher. I got a positive going through Bucharest Airport, they asked me my job and let me go through once they found out. They took repeat samples, the first was a trace positive, the other two negative.

  10. please note these machines are also calibrated to detect narcotics which may also be one of the reasons some of you have been checked again

  11. My husband’s ashes set off the explosive detector. My goodness, I was hard put not to laugh as TSA backed off and apologized.

  12. Can anyone tell me what an E13 alarm means when screening cargo using anow ETD machine ( IONSCAN 500 ST ) ?
    Thanks

  13. I was swabbed along with 3 other passengers unknown to me, only one swab was used on all 4 passengers at precisely the same time then put into the sniffer machine, is this correct? I took this up with the airport afterwards but they waffled around an explanation stating that the ETD was performed in accordance with the requirements of The Australian Government. I do firmly believe that this exercise was definitely not carried out correctly. Please advise.

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