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┬ácan 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:

– TNT (Tri Nitro Toluene)
– Semtex
– Tetryl
– Nitroglycerine (NG)
– Nitrates
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.