Comments on: Blowing air from airport security.

Question: Blowing air from airport security.

Sreiny — Sun, 05 Feb 2006 21:48:58 -0800

I went through airport security today, and had to go through a large apparatus that blew bursts of air at me from about 30 little air jets. What was that? What does it do? What were they looking for?

This was at the Indianapolis International Airport for those who were wondering. I'd never seen it before. It was like an oversized metal detector that you walk into, stand in the middle and then are shot with air. The air nozzles are from the floor to about six feet high and shoot air progressively down your body. Interesting contraption.

By: rob511

rob511 — Sun, 05 Feb 2006 21:55:05 -0800

Did they ask you to sing, "Happy Birthday, Mr. President"?

Seriously, those are the new puffers, designed to test for explosive traces that might be lodged in terrorists' clothing and skin folds.

By: scoria

scoria — Sun, 05 Feb 2006 21:57:16 -0800

Could it have been a new explosives screening device? Indianapolis International Airport is known to have them.

The bursts of air are intended to release microscopic particles on your skin or clothing, which are then inspected for any residue that might indicate the presence of an explosive device.

By: smackfu

smackfu — Sun, 05 Feb 2006 21:59:28 -0800

The same machines can also detect narcotics as a side-benefit. Woo.

By: loquax

loquax — Sun, 05 Feb 2006 22:00:34 -0800

They use those at the CN Tower in Toronto too. Why didn't you ask? I sure did when they asked me to step into a bizarre nozzle-filled chamber.

By: rob511

rob511 — Sun, 05 Feb 2006 22:07:05 -0800

Not to hijack, but has anybody gone through the backscatter X-ray machines that the TSA was supposed to install at the end of '05? (Shades of Total Recall!)

By: ikkyu2

ikkyu2 — Sun, 05 Feb 2006 22:34:29 -0800

Does it detect anything besides explosives? I've heard that some of these can detect drugs and/or cash.

By: disillusioned

disillusioned — Mon, 06 Feb 2006 01:33:40 -0800

ikkyu2- Please to see smackfu's comment.

The machines are pretty neat... They blow the particulates and based on their molecular weight, they'll each fall a certain distance apart, which is used to categorize them. What will they think of next?

By: elisabeth r

elisabeth r — Mon, 06 Feb 2006 04:56:12 -0800

Were you warned that you were going to have air blown at you from several tiny airjets? Because I'm easily startled, and this would scare the pants off me.

By: intermod

intermod — Mon, 06 Feb 2006 05:57:49 -0800

They blow the particulates and based on their molecular weight, they'll each fall a certain distance apart, which is used to categorize them.

disillusioned, do you have a source to back that up? I seriously doubt it works the way you make it sound: particles blown off then fall to a collector array that discriminates molecular weight based on where they fall. That would take forever to do, far more than the 15 seconds claimed.

What's more likely is that the air is sucked back in somewhere and run through detectors. Now, inside those detectors it's certainly likely that there's some sort of molecular weight discriminator thing going on that uses acceleration, but on a microscopic scale. Probably a molecular analyzer that looks for certain known signatures -- there are plenty of benign things that have heavy molecular weights (e.g. plastics), so they can't just discriminate on weight.

No details in the above links ...

By: ludwig_van

ludwig_van — Mon, 06 Feb 2006 05:57:54 -0800

I went through one of these for the first time recently and was rather bewildered as well, so I'm glad you asked this question. I believe it was in the Philadelphia airport, though I may be mistaken, as I've been through several recently. I wasn't warned about what it was going to do, and the air jets were indeed rather startling.

By: Mitheral

Mitheral — Mon, 06 Feb 2006 06:46:47 -0800

rob511 writes "those are the new puffers, designed to test for explosive traces that might be lodged in terrorists' clothing and skin folds."

Yep, make sure you haven't been fertilizing the lawn in the last few weeks when flying.

By: furtive

furtive — Mon, 06 Feb 2006 06:51:22 -0800

Heh, I'm rubbing some hexamine fuel tablet on my jacket next time I go through the airport to see what happens.

By: bonehead

bonehead — Mon, 06 Feb 2006 07:06:35 -0800

It's an ion mobility spectrometer (IMS). There's a paper describing how one of these machines is built here (PDF). These machines are sometimes known as "artificial noses".

How these work:

A puff of air off your body is slurped into a small chamber. In this chamber is a cloud of very low energy (<<eV) electrons. Any strongly electrophillic chemicals in the air will grab one of these, making a negative molecular ion. Electrophillic species are those that have lots of nitrogen, phosphorus, or oxygen in them. Most illegal drugs, explosives and chemical warfare agents are all strong electrophiles.

The ions are then drawn through a small hole (by a weak positive charge), accelerated across a large electric gradient to give them all the same kinetic energy (since all the ions have the same charge: -1). Since each chemical has a different mass, their speeds will be different (remember that KE=1/2mv²).

After being sped up, the ionized molecules drift freely down a longish tube to another plate. When a molecule hits the plate, it dumps its extra electron. So, for each molecule passing through the system, a small electric pulse is generated.

Now remeber that each type of molecule is travelling at different speeds becasue their masses are different. By timing the electric pulses recorded at the end of the drift tube, it's possible to figure out that cocaine takes so long, that TNT travels this fast, and so on. The machine is setup to beep if it sees a chemical that hits the collector plate in one of these interesting times.

So: the machine slups up the air, ionizes it, accelerates the ions through a drift tube and discriminates based on the molecular time of flight. It works best for strong electrophiles, which includes most drugs, explosives and chemical-warfare agents. Done right, these things are extremely sensitive. I've seen a person handle a double-wrapped brick of C4 (no direct contact), then wash his hands and subsequently set-off the machine. There was a real concern that the high level of cocaine in US money would cause problems for these things.

These machines have serious downsides though. They will only detect chemicals that their makers have programmed in to them. If some bright bunny comes up with a new drug or explosive, the machine won't see it. These things have other problems too: ion generation is quite tricky---high humidity is a real problem for these machines. Also, the acceleration timing is hard to get right. These things have a long history of false positives.

Incidentally, these are the same technology as the machines that are used for swabbing electronics.

By: Faint of Butt

Faint of Butt — Mon, 06 Feb 2006 07:22:28 -0800

Could you defeat this (and really piss off the security guards) with a liberal application of talcum powder?

By: bonehead

bonehead — Mon, 06 Feb 2006 07:35:43 -0800

You'd need a fair bit of suspended matter to clog the filters. It would be pretty obvious.

By: whoda

whoda — Mon, 06 Feb 2006 07:36:40 -0800

Faint, having any sort of powder which comes off of you in big enough quantities to be noticed is probably going to get you detained for questioning extremely quickly no matter what else you do.

By: bonehead

bonehead — Mon, 06 Feb 2006 07:42:07 -0800

Incidentally, while it's a good candidate compound, I'm not sure the detectors would be calibrated for hexamine. If you don't mind the body cavity search and possible criminal charges, it might be an interesting experiment to try.

By: CunningLinguist

CunningLinguist — Mon, 06 Feb 2006 07:48:00 -0800

make sure you haven't been fertilizing the lawn in the last few weeks when flying.

Also, no shit, don't use moisturizer. Many have glycerin in them and the test for nitroglycerin can come back with a false positive. I got pulled into a little room in Des Moines once because my shoes tested positive for explosives. I was completely freaked out. Turns out I had used the hotel lotion on my hands just before tieing my sneakers.

By: cactus

cactus — Mon, 06 Feb 2006 09:14:42 -0800

I've been through a few of the puffers, even at the Liberty Bell exhibit in Philly. I didn't set them off, but a buddy of mine, a combat engineer, did when he went on leave from Iraq and used his demo bag as luggage. Caused quite a ruckus.

rob511: They've installed the backscatter x-ray machines at the Tijuana border crossing but I haven't seen them anywhere else.

By: cybercoitus interruptus

cybercoitus interruptus — Mon, 06 Feb 2006 09:41:46 -0800

Thanks for asking this from me too. I went through one at Christmas and asked the security guy who waved me into it what it was all about. He completely ignored me.

By: deaddodo

deaddodo — Mon, 06 Feb 2006 10:34:03 -0800

I got backscattered at Heathrow. I had to hold three different poses (all with feet at diagonals, then arms up, arms down, front and back). I think they were trying to find the best way of seeing everything.

I was going to ask for a peek at my nekkid pictures, but they really weren't in the mood for jokes.

By: five fresh fish

five fresh fish — Mon, 06 Feb 2006 10:35:31 -0800

Make sure you fart loud and long while its running.

By: Ogre Lawless

Ogre Lawless — Wed, 08 Feb 2006 11:58:20 -0800

SFO was using the puffer for domestic-traveling "objectionables" (my term) who for whatever reason got the second-level TSA screening. This appeared to be a replacement for the old "sit in this chair while we very vigorously wand you" methodology, but I could have just missed that.

Candidates on line when I went through the "good person" line were the hippie chick going to Hawaii who insisted that her 200-speed film MUST NOT BE X-RAYED OR ELSE IT WOULD BE RUINED and a startled-looking traveller for whom English was not his principal language.

I assumed the GE-branded machine was doing a bit more than puffing, but maybe that's it?

By: cavalier

cavalier — Thu, 09 Feb 2006 13:31:54 -0800

Saw this at MIA (Miami).. had a lot of time to kill but there was only one machine and a huge line compared to the rest of the scanners.. I saw the huge "GE' contraption and I thought 'cool! what's that fer!'

By: dejah420

dejah420 — Wed, 22 Feb 2006 17:10:35 -0800

Wow, if it's really that sensitive, and if glycerin sets it off, and I'm sure sodium hydroxide will set it off...as a soap maker, I think I may be screwed.