This just adds confusion as to the purpose of all this.

The motivation behind the liquid limits is that there are extremely powerful explosives that are stable water-like liquids. Average people have never heard of them because they aren’t in popular lore. There has never been an industrial or military use, solids are simpler. Nonetheless, these explosives are easily accessible to a knowledgeable chemist like me.

These explosives can be detected via infrared spectroscopy but that isn’t going to be happening to liquids in your bag. This reminds me of the chemical swipes done on your bags to detect explosives. Those swipes can only detect a narrow set of explosive chemistries and everyone knows it. Some explosives notoriously popular with terror organizations can’t be detected. Everyone, including the bad guys, knows all of this.

It would be great if governments were more explicit about precisely what all of this theater is intended to prevent.

Correct. In the US, the TSA is just a government jobs program for the lowly skilled or unskilled. It's all security theater.

TSA Chief Out After Agents Fail 95 Percent of Airport Breach Tests

"In one case, an alarm sounded, but even during a pat-down, the screening officer failed to detect a fake plastic explosive taped to an undercover agent's back. In all, so-called "Red Teams" of Homeland Security agents posing as passengers were able get weapons past TSA agents in 67 out of 70 tests — a 95 percent failure rate, according to agency officials."

https://www.nbcnews.com/news/us-news/investigation-breaches-...

It's about making people feel safe.

We're not rational beings, so what do you do about an irrational fear? You invent a magical thing that protects from that irrational fear.

You're orders of magnitude more likely to die in a road accident, but people don't fear that. They fear terrorist attacks far more.

You can't protect against an opponent who's motivated to learn the inherent vulnerabilities of our systems, many of which can't be protected against due to the laws of physics and practicality - short of forcing everyone to travel naked and strapped in like cattle, with no luggage. And even then, what about the extremist who works for the airline?

So you invent some theater to stop people from panicking (a far more real danger). And that's a perfectly acceptable solution.

On one hand, I think it's a valid criticism to say it's security theatre, to a degree. After 9/11, something had to be done, fast!, and we're still living with the after effects of that.

On the other hand: defence in depth. No security screening is perfect. Plastic guns can get through metal detectors but we still use them. Pat downs at nightclubs won't catch a razor blade concealed in someone's bra. We try to catch more common dangerous items with the knowledge that there's a long tail of things that could get through. There's nothing really new there, I don't think?

> Average people have never heard of them because they aren’t in popular lore.

Everything I know about liquid explosives I learned from Die Hard 3.

most of airport security rests on the notion of going over a series of long tests will elicit unusual (fear, stress) responses from malicious actors and these can then be flagged for even thorougher checks which will then eventually lead to discovery, banning or removal of luggage

so it's not the test accuracy by itself but rather then the fact that these tests are happening at all

> The motivation behind the liquid limits is that there are extremely powerful explosives that are stable water-like liquids.

The limits were instituted after discovering a plot to smuggle acetone and hydrogen peroxide (and ice presumably) on board to make acetone peroxide in the lavatory. TATP is not a liquid and it is not stable.

https://en.wikipedia.org/wiki/2006_transatlantic_aircraft_pl...

In Zurich, you can buy Swiss army knives in the secure zone.

Security theater and conditioning people into accepting invasions of privacy

These liquids show up as slightly different colors in the new CT scan machines and this can finally be reliably detected by software.

This is also why a bunch of airports no longer ask you to take electronics out of your bags.

From my understanding, the new CT machines are able to characterise material composition using dual-energy X-ray, and this is how they were able to relax the rules.

I'm fine with some liquid potentially being explosives, but the fact that security just throws them all in the same bin when they confiscate them makes me think that not even they believe it makes any sense.

Also, why 100ml? Do you need 150ml to make the explosive? Couldn't there be 2 terrorists with 100ml + 50ml? All these questions, so little answers...

I believe the "theater" is needed precisely for this - to catch bad actors. There could just be a long queue with some blind dog and scary looking guy at the end. What it still does is makes a bad guy sweat, plan against it and etc. You just can't have free entrance for all. However you will never prevent state actors or similar with any kind of theatre because they will always prepare for it.

Is a open flame enough to ignite those liquids and don't they need something to press against to "explode" and not just cause a giant flame like gasoline?

I thought the point of replacing all the xray scanners with CT scanners was to be able to detect this sort of thing?

> These explosives can be detected via infrared spectroscopy but that isn’t going to be happening to liquids in your bag

There are more ways to find them. Look up Z score. TL; DR New detectors can discriminate water from explosives. Old ones couldn’t. None of them are doing IR spectroscopy.

So how does that explain I can take 10 100ml bottles and an empty 1l bottle through security but not 1 full 1l bottle?

Won't asking people to take a swig solve a bunch of those issues?

OP is talking about (mostly) TATP here. It's very easy to make, harder to detect with traditional methods and potent enough to be a problem. It's also hilariously unstable, will absolutely kill you before you achieve terrorism, and if you ask people on the appropriate chemistry subreddits how to make it you'll be ridiculed for days.

> . This reminds me of the chemical swipes done on your bags to detect explosives. Those swipes can only detect a narrow set of explosive chemistries and everyone knows it.

Meanwhile, you get swabbed, the machine produces a false positive, the TSA drone asks you why the machine is showing a positive, you have no fucking idea why, and they just keep swabbing until they get a green light and everyone moves on with life.

The security theatre is there to make people feel safe.

It's about emotion not logic.

I wonder if the improvements can detect trigger mechanisms better rather than testing the liquid itself.

how does it add confusion?

if normal people don’t know, criminals/terrorists do, and the materials are commonplace but not screened for, then everything about the current approach is wrong.

and when has a plane been brought down by the evil explosives or stable liquids in recent memory?

so the theatre put in place is just that, huh?

> Everyone, including the bad guys, knows all of this.

Then satisfy our curiosity and provide more details as to which are the liquid explosives and which common ones are not detected ? ;)

> It would be great if governments were more explicit about precisely what all of this theater is intended to prevent.

Have you considered just going long Palantir?

there's nothing to really understand

Security theatre.

And speaking of theatre in the air, most Indian airlines will make an announcement of turbulence just before food service starts.

This is to make the sheep - strike that - passengers go back to their seats and sit down.

It's obvious. The harder you make it to down or hijack a plane, the fewer downed planes you will see. It didn't have to be perfect to prevent and deter. Some security is better than no security. If you had no security at all you would see planes go down all the time.

And it wouldn't surprise me if some of the detection technology were classified.

It would not be "great" if governments were more open about their detection capabilities; that would cause more terrorism attempts and is one of the stupidest things one could do here.

Ahh, the naïvety of the scientific mind! The security theater is intended to prevent government beaurocrats' mates from having to get real jobs and keep them happily sponging off public money. Also, set themselves up for post-career high paid gigs with those same private sector beneficiaries, so they can't be done for corruption during their career. Yes, really. Ask an AI about mid to late career public sector transitions to private sector and cross-examine 100 top examples across markets perceived as 'low corruption index'.