Eine Kleine Nichtmusik

Witty and pertinent observations on matters of great significance OR Incoherent jottings on total irrelevancies OR Something else altogether OR All of the above

Thursday, April 03, 2008

You can't change the laws of physics....

....as Star Trek's Scotty used to insist. Funnily enough, though, the "terrorism experts" who advise the Home Office seem to imagine that those laws, when applied to chemical reactions, take on a much more malleable and provisional form. The news is full right now of the trial of the men who plotted to cause "mass murder on an unimaginable scale" by using liquid explosives to destroy transatlantic aircraft.

What a pity it wouldn't work. At worst the bombers might have managed to set the aeroplane toilet on fire. If they actually made something big enough and strong enough to destroy an airliner (and the link to the article about Aloha Airlines Flight 243 shows that it ain't that easy) they'd undoubtedly have attracted suspicion when carrying their ice-packed payload aboard. Either that or they'd have made a series of neat holes in the ground when their taxis went over speed bumps.

But wait! What's this? Now we hear rather than TATP the dastardly brown chappies were planning to use HMTD. (Or maybe that was only the detonator: though why would they need one, since apparently hydrogen peroxide itself is capable of being "detonated to deadly effect".)

Let's ignore for now the game of if-we-change-the-accusations-often-enough-and-use-enough-confusing-abbreviations-people-will-stop-trying-to-follow-the-arguments-and-assume-the-experts-know-best that's going on here. Let's ignore even the fact, readily verifiable via the links above, tha HMTD and TATP share similar drawbacks for the job under consideration. Maybe slightly less fumes from HTMD synthesis, but that's all. Let's just return to our prosecutor, briefed by our government's experts in explosives and terrorism, telling us that hydrogen peroxide can be detonated. Well, here's some information on hydrogen peroxide.

Spilling high concentration peroxide on a flammable substance can cause an immediate fire fueled by the oxygen released by the decomposing hydrogen peroxide. High strength peroxide (also called high-test peroxide, or HTP) must be stored in a vented container to prevent the buildup of oxygen gas which would otherwise lead to the eventual rupture of the container. Any container must be made of a compatible material such as PTFE, polyethylene or aluminium (not stainless steel) and undergo a cleaning process (passivation) to remove all contamination prior to the introduction of peroxide. (Note that whilst compatible at room temperature, polyethylene can explode with peroxide in a fire.)

I've seen the spilling-HTP-onto-a-piece-of-clothing trick demonstrated (when I attended my first RAF camp as an Air Training Corps cadet at school - it was part of the fuel for the air-launched nuclear missiles deployed on 617 Squadron's Vulcans.) Combustion, certainly, but no detonation. Difficult to make the stuff at home, and any attempt to smuggle that sort of hydrogen peroxide concentration in Gatorade bottles would pretty much guarantee a steep rise in London's reported cases of spontaneous human combustion. No, I think I'm more worried about policy being dictated by self-styled "explosives experts" who don't know the difference between detonation and deflagration than I am by supposed "Islamic fanatics" arrested for having flight timetables on a memory stick.

It's easy to see where this is going, though. Play on the public's ignoraance of chemistry, persuade the ignorant that this was a real plot with real explosives, then when the jury throws the whole thing out after someone explains the science to them the government can "prove" that jury trials allow "terrorists" to walk free, maybe with a side order of clever defence lawyers "confusing" the jury.

The author of the piece in The Register worried that real terrorists who do understand chemistry would be operating unhindered while the credulous oafs charged with our protection worrried about all the wrong things. Undoubtedly true, but in my opinion it' s less about catching terrorists than about discrediting due legal process.

Update: more interesting discussion here, here and especially here.

Also here, here and here.

And in case the somewhat flaky nature of the last link worries you, the British Army think it's bollocks as well.

Yes, I think Britain and the USA are finally beginning to "get it" about the "war on terror".


At 10 April, 2008 22:42, Blogger Sal said...

umm. i hate to risk sounding rude, especially after you were so nice to me above, but although i agree with you about the security theatre being just that, the materials they had really were capable of being used safely (pre-detonation :) ) and of being more than powerful enough to bring down the aircraft.

your points re deflagration vs detonation are all valid, as are the points re LONG-TERM storage of one of the ingredients pre-admixture.

nevertheless, those chemicals are more than capable of being used in the manner intended in a completely stable, safe, and near-undetectable fashion. the "secret"'s in the proportions, just like most explosives. petrol vapour (in air) is effectively inert unless spot on 10,000ppm. nitroglycerine will explode if tapped hard but dynamite can be thrown on the fire. slightly wrong gunpowder is just non-burning antibiotic batshit. give me a bag of fertiliser, a petrol station, and £1, and i can give you with 10 seconds work (and a few hours "curing" time) the globally standard industrial-strength commercial explosive-- totally stable sans detonator. (and if you're RAF-trained, you probably can too)

i've answered properly elsewhere, -- if you have 2 minutes, have a look at that post then read my comments below it.

>actually, all the professional high-yield explosives in the US (eg, used by police & FBI explosives specialists) are (clear) liquids, with slightly higher post-mix yield (by volume) than dynamite. so 300ml is more than sufficient to bring down an aircraft and even 100ml could do it if used "sensibly", eg placed & braced against the fuselage by say wedging a vial between wall & chair leg on a window seat. they are stable at quite high temperatures in a normal-living sense (eg, under summer time california sun) both before and after mixing.

so, much though i loathe security-theatre, in this case it's a valid concern.

>>"Some people are confusing deflagration and catalytic decomposition of peroxide mixtures with detonation. The way HTP is used as rocket fuel is not comparable to its use as an explosive. Proper HTP mixes are powerful and brisant high explosives, on a par with TNT or better."

At 11 April, 2008 03:50, Blogger Rob said...

But as I understand it organic peroxides are not the kind of stuff you sling about gaily unless you intend to lose digits: plus acetone peroxide is a crystalline rather than a liquid. It was the precursor chemicals they were supposed to be intending to take aboard the aircraft. I don't deny that these are capable of being turned into explosives in the loo, but without lot of care and (especially) attention to cooling the mix will explode when only a little of it has actually formed the explosive end-product. By definition it will do that wherever you're trying to make your explosive, not where you'd like it to be placed to bring down the aircraft. And if you sort out the cooling somehow, the process takes longer than most tranatlantic flights.

Now if they'd smuggled aboard a load of carbon tetrachloride and sulphuric acid with the intention of gassing economy class with phosgene, I'd agree on the practicality. Or formic acid to make carbon monoxide (harder to detect, easier to treat victims). But the whole TATP thing is a non-starter.

At 12 April, 2008 22:05, Blogger Sal said...

yeah, if that was what they were going to do, all your observations are quite valid. in which case, the court case will rest on their intent to do the deed, regardless of their poor competence to fully achieve the deed. similar to if i attack you with a knife but it turns in my hand and bounces off your throat -- "attempted murder" only.

but here's the key point (which i clearly made poorly): the precise details of _exactly_ how they were intending to _use_ those chemicals was not documented and is now unlikely to be admitted to, and as is pointed out in that thread, their documentedly intended means of taking the chemicals on board was in a form which could have been the raw chemicals, or could just as easily have been preprepared chemicals in a stable but fully explosive state.

At 13 April, 2008 14:35, Blogger Rob said...

I agree the court case should hinge on intent: the question is whether so much concentration on their supposedly sophisticated chemistry will end up sowing doubt in the jury's minds and getting the whole lot flung out. Which might fit with the government's overall intention but can't be good news in general. Depends precisely how the charges are framed.

You'll just have to colour me unconvinced regarding the carry-on stability of ready-mixed "clear liquid" explosives in general. However, going by what chemicals they had, our current bunch were planning to make TATP or something similar. They could have mixed it in the bath all right, but the end product is a powder (or a slurry which has to be dried out before use) not a liquid. Now if the authorities had started getting worried about baby powder and such, it would have made more sense. This guy agrees.

Of course the really dumb thing is that even with the current liquid limits a single terrorist could take on board enough dimethyl mercury (colourless, highly volatile,absorbed through the skin even with rubber gloves on, and 10 ml is a fatal dose for 10,000 people) to wipe out everyone on a plane. OK, they'd probably mostly die after landing, but the fear factor once people realise that they could be murdered without even knowing until it's too late would be huge.


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