So What Are These Liquid Explosives?

by CKR

My curiosity is piqued. I hadn’t paid much attention to this business of liquid explosives until last week. Nitroglycerin, yes, is an explosive liquid. But which are the exciting compounds are that are odorless and inert by themselves and detonate when mixed?

After googling a few pages of links to uninformative news stories, QandO reminds me of GlobalSecurity.org, who list some liquid and sort-of-liquid explosives, although the article lapses back into a discussion of cartridged explosives, which are solid or at least pasty or gels. None of these liquids or mixtures, however, fit the sensational news descriptions of inert compounds that magically detonate when mixed.
Nitroglycerin. Very sensitive. Already said that.
Astrolite, a mixture of ammonium nitrate and anhydrous hydrazine
Nitromethane with a sensitizer
Kinepak, a mixture of ammonium nitrate and nitromethane
Binex, a mixture of a sodium perchlorate solution and aluminum powder.

Ammonium nitrate is grass fertilizer. It's a solid. It can be mixed with things like fuel oil to make explosives, as was done for the Oklahoma City bombing. It can explode by itself, too. The enormous Texas City explosion of 1947 was of a shipload of ammonium nitrate. Apparently anhydrous hydrazine can dissolve it to form a liquid that is called Astrolite. Anhydrous hydrazine is also known as rocket fuel and is considered an explosive itself. Anhydrous means that it doesn’t have any water in it, and that adjective is usually applied to substances that pick up water easily. You’ve seen how sugary things can sort of melt on a humid day. The sugar is dissolving itself in water pulled from the air by chemical attraction. Hydrazine picks up water that way too. It’s a poison and is hard to buy, unless you’re NASA.

Nitromethane is easier to buy. It’s used in model airplane engines and drag racers. It’s extremely flammable. The sensitizers are amines and other things that are hard to buy. Since nitromethane is more energetic than fuel oil, ammonium nitrate can be combined with it in the same way to produce an explosive that is a paste or moist powder, not a liquid. The two components don’t have to be stored as explosives, which simplifies things for commercial handlers. We’re talking about regulations, having the proper signs and transporting and storing them in the proper ways. Terrorists don’t care about that. Nitromethane is a liquid, but ammonium nitrate is a solid, and the mixture is a paste or moist powder.

For Binex, the sodium perchlorate solution is a liquid, and powdered aluminum is a solid. Seems to me because the aluminum would fall to the bottom of the solution. I don’t know whether this would make a difference to its explosive qualities, but I suspect it would. So a gel or suspension would be necessary. Most of the gelling agents are organics, though, and I’m wondering if they wouldn’t react with the perchlorate prematurely.

So how do all these stack up against the sensational claims in the media?

None are two liquids that detonate when mixed together.

The only ones that are liquids are nitroglycerin, Astrolite, and sensitized nitromethane. You can’t get anhydrous hydrazine for Astrolite on the open market, and even if you could, it’s very, very hard to handle. The nitromethane sensitizers are difficult to obtain.

The GlobalSecurity.org article is confusing, but I think it says that all the mixtures need a blasting cap to set them off. This is more than the electrical detonators described in the media; a blasting cap has an electrical detonator attached to a primary (sensitive) explosive. It is the primary explosive that then sets off the main charge. We can hope that the TSA x-ray readers know what a blasting cap looks like.

Most of these components are pretty stinky, far from odorless. The perchlorate solution with aluminum would come closest to odorless. The odor of the amines for sensitizing nitromethane starts from dead fish and gets worse. It really doesn’t come off your hands, either.

There’s also a question of how much is needed. Nitroglycerin is one of the more powerful explosives in this group. A Russian expert estimates that one to one and a half kilograms of nitroglycerin would be necessary to bring down an airliner. Nitroglycerin is much denser than water, so that amounts to between one and two. Gatorade bottles would indeed be required for something like that, hardly those little tubes of hand cream some of us carry in our purses and for which a transatlantic flight was diverted yesterday.

Bottom line: There are a few more liquid explosives in addition to nitroglycerin, but the scenarios we’re hearing from the media would be very, very hard to carry off, some impossible. Unless there’s still more kinds of liquid explosive out there, and, oh yes, all those things that the government can’t tell us, but the terrorists know…

Comments

[Xan]

Cheryl, thanks for the crib sheet. I keep hearing talk (CBS News just tonight, and other sources earlier) going on and on about hydrogen peroxide. However the bottles they showed on the tape as being picked up as "terrorist bomb-making supplies" in the local park looked just like the bottles of the 3% shit I pick up at the grocery when I need to clean wax out of my ears.

What concentration of h. peroxide would be needed to be all or part of an explosive, how many bottles of the common 3% would be needed to make the requisite airliner-bringing-down amount, and how...well, you probably wouldn't want to tell how to get it concentrated enough here on an open board, so let me phrase it as "how likely is it that these apparent stone amateur chemists could achieve this feat and then carry it onto the plane afterwards"?

[CKR]

The reports I've seen are that the British investigators picked up a suitcase that contains "chemicals, hydrogen peroxide, and electrical components." This doesn't tell us much. My carryons (and most people's) could be described in the same way if I put hydrogen peroxide in them, which I don't. I didn't see any pictures of the contents, so I can't comment on that.

I don't know about the TATP synthesis from experience; as I said earlier, I haven't worked with explosives myself, but I've worked closely with people who do, and they stayed away from explosives as sensitive as TATP and nitroglycerin. However, as I pointed out before, my colleague Jimmie Oxley doubts that TATP is strong enough to bring down a plane. Probably enough would do the trick, but if you need a liter or so of nitroglycerin, you might need a few pounds of TATP.

The Wikibooks synthesis of TATP says you can use 3% hydrogen peroxide, but it also says that higher concentrations will give you more product more quickly. You can boil the hydrogen peroxide to concentrate it, but this risks setting things on fire. Handling concentrated hydrogen peroxide is something I did look into for one of my projects, and it's harder than you might think. It also may contain stabilizers that would also be concentrated and might interfere with a synthesis. My 3% solution doesn't say it contains stabilizers, but the label isn't too informative. It's very old. I don't use it much.

I've seen 70% hydrogen peroxide mentioned for syntheses. Twenty-some bottles of 3% hydrogen peroxide equal one bottle of 70%.

I wasn't explicit about my judgment of the probability that amateurs could successfully carry off the synthesis. I would put it at very low. There's the danger of fire with hydrogen peroxide, the danger of explosion or fire during the synthesis and handling of the crystals, and the danger of explosion in transporting the crystals around. Concentrated sulfuric acid has its own dangers; I've had jeans and labcoats dissolve in the wash after I've used it and didn't think I was splashing it around. It can cause nasty burns on your skin.

The nearest I can figure to the magic "two inert liquids mixed to detonate" is concentrated hydrogen peroxide and acetone. But they wouldn't detonate. Most likely, the worst you would get is a quick flash of flame, maybe a puff or small bang. It would be upsetting, but it wouldn't necessarily bring down a plane.

[Jimmie Oxley's comments and this last paragraph depend on the difference between detonations, deflagrations, and rapid exothermic reactions. I won't go into that much technical detail unless someone asks me to, but those terms refer to how rapidly the energy is released, the most from a detonation. That, in turn, determines how much damage they can do.]