What explosives were to be used on the UK planes?

Watching the news coverage today, I found myself wondering what type of explosive the terrorists were trying to use on the UK planes. I did a web search, and many news services are speculating that the chemical in question could be one called Triacetone Triperoxide.

i-3b2f79af3008fd5cf6769f98b0497d2a-220px-Acetone_peroxide.jpg

Shown above triacetone triperoxide (also called acetone peroxide, peroxyacetone, TATP, or TCAP) is an unstable white powder that is formed from the reaction of hydrogen peroxide and acetone with a strong acid catalyst. From Wikipedia:

Also known as "peroxyacetone", acetone peroxide most commonly refers to the cyclic trimer TCAP (tri-cyclic acetone peroxide, or tri-cyclo), also called triacetone triperoxide (TATP), obtained by a reaction between hydrogen peroxide and acetone (using a catalyst). The cyclic dimer (C6H12O4) and open monomer and dimer are also formed, but under proper conditions the cyclic trimer is the primary product. A tetrameric form was also described. In mildly acidic or neutral conditions, the reaction is much slower and produces more monomeric organic peroxide than the reaction with a strong acid catalyst. Due to significant strain of the chemical bonds in the dimer and especially the monomer, they are even more unstable than the trimer.

At room temperature, the trimeric form slowly sublimates, reforming as the less stable, more sensitive dimer.

TCAP generally burns when ignited, unconfined, in quantities less than about 2 grams. More than 2 grams will usually detonate when ignited; smaller quantities might detonate when even slightly confined. Completely dry TCAP is much more prone to detonation than the fresh product still wetted with water or acetone. The oxidation that occurs when burning is:

2 C9H18O6 + 21 O2 --> 18 H2O + 18 CO2

The explosive decomposition of TCAP, in contrast, results in "formation of acetone and ozone as the main decomposition products and not the intuitively expected oxidation products." [1] It is the rapid creation of gas from a solid that creates the explosion. Very little heat is created by the explosive decomposition of TCAP. Recent research describes TCAP decomposition as an entropic explosion.

The extreme shock, heat, and friction sensitivity are due to the instability of the molecule. Big crystals, found in older mixtures, are more dangerous, as they are easier to shatter - and initiate - than small ones.

More from Scientific American:

Chemists in the Department of Homeland Security (DHS) have declined to comment on the composition of the explosive, but news of the terror plot has sparked considerable speculation about what chemicals were involved--and what ones future terrorists could employ. The laundry list of chemicals that could conceivably be used--in either liquid or solid form--is essentially endless, given the proper expertise. "There a lot of liquid explosives," says chemist James Tour of Rice University, who works on retarding chemical weapons attacks. "There are books on these things." But terrorists often employ the same or similar compounds. Favorites include triacetone triperoxide (TATP) and nitroglycerin, the components of which are individually harmless, but dangerous when combined.

Neither of these is easy to work with, however. TATP is an atypical explosive, relying as it does on the formation of four gas molecules for every solid TATP molecule when triggered--a powerful "entropy burst," as researchers have called it. But TATP is relatively unstable--simply hitting the powder can set off the reaction--and it requires some time to produce the compound. Terrorists would have to blend the constituent chemical brew and then wait for the explosive powder to precipitate over the course of the next day, according to Tours, making it unlikely to be made on board a flight. Nitroglycerin--the explosive ingredient in dynamite (and a common heart medication in small quantities)--would be even more difficult to handle if made on board; early experimenters suffered a slew of explosive mishaps due to its volatile nature. And many other explosives immediately fume or otherwise react as the chemicals are blended, as well as being highly sensitive to jostling. "Peroxides are very dangerous and shock sensitive," notes one university chemist who asked not to be identified.

The New York Times reports on a memo suggesting that this might be the type of explosive used:

A memo issued by federal security officials about the new plot highlighted a type of liquid explosive based on peroxide.

The most common peroxide explosive is triacetone triperoxide or TATP, which is made from two liquids: acetone, the primary ingredient of most nail polish removers, and hydrogen peroxide, commonly used as an antiseptic when diluted. TATP, which can be used as a detonator or a primary explosive, has been used in Qaeda-related bomb plots and by Palestinian suicide bombers.

I don't know that this is definitely the explosive that these guys were planning to use. It is possible.

It is made from commonly available materials -- some nail polish has acetone and hydrogen peroxide is available in the drug store. However, both ingredients from the drug store are heavily diluted. I think that the drug store stuff is only 3% hydrogen peroxide. That being said, I am sure someone savvy could get higher concentrations, and I am not certain the concentrations you would need to get an adequate yield.

Also, peroxyacetone is not a liquid so I am not certain where that piece of info fits in. It is a very, very unstable powder. This suggests that it would be very difficult for terrorists to even get it to the airport without blowing themselves up in the process. Most of the stuff that I read about it suggests that even making this stuff can be a very hazardous profession.

I suspect that even small quantities of the stuff would be effective at blowing a hole in a plane. Its explosive velocity is 5300 m/s (by comparison the explosive velocity of nitroglycerin is 7700 m/s). News reports have been suggesting that the detonator to be used was some kind of small battery such as the charger on a disposable camera flash or a cellular phone:

Terrorists could easily slip a few apparently innocuous items past airport security and assemble them into a lethal explosive once aloft, security experts said.

Some envision a group of two or three terrorists mixing up explosives in an airplane bathroom, perhaps even using commonplace materials such as hydrogen peroxide and detonating their bomb with the battery from a cellphone or some other small electronic device.

"In mid-flight you could go into the toilet, attach the mobile phone to the explosives and, as the plane makes a final approach over a densely populated urban area, you detonate it," said Irish security analyst Tom Clonan.

To puncture an aircraft's fuselage would require an explosive charge "half the size of a cigarette packet," he said. (Emphasis mine.)

My gut instinct says that this is reasonable, but frankly I don't know enough about chemistry to tell what other choices they would have. Any chemists who know more want to weigh in on this?

UPDATE: Molecule of the Day has a more educated look. Read the whole thing.

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By somnilista, FCD (not verified) on 11 Aug 2006 #permalink

Since acetone peroxide is not a liquid, it probably was a different organic peroxide (possibly MKEP). The wikipedia entry on the terrorist plot has a decent write up on the types of explosives that might have been used.

Scrupulously pure MEK peroxide is a solid, see here. A liquid formulation of acetone peroxide (or, obviously, MEK peroxide) is a possibility, but they're still rattlesnakes. Oftentimes, really sensitive stuff like this (see, for example, Derek Lowe's entry on polyazides) will detonate with no more provocation than a touch with a 5mm metal spatula. The n-ammine nitrogen triiodide complex, for example, can be ignited with the literal touch of a feather. For some horror stories and more info, see the Yarchive entry on peroxides.

Nitroglycerin--the explosive ingredient in dynamite (and a common heart medication in small quantities)--would be even more difficult to handle if made on board; early experimenters suffered a slew of explosive mishaps due to its volatile nature.

Not true. Nitroglycerine is not nearly as sensitive as portrayed in the movies and in common folklore. I used to fill plastic tubes with it and throw it as far as I could down the street. It never went off until the detonator set it off.

Of course it is too sensitive to be used commercially and that's why it's mixed with powders to plasticize it.

Also, volatile does not mean what most people think it means. It means prone to evaporation. Nitroglycerine is not particularly volatile.

By Riesz Fischer (not verified) on 12 Aug 2006 #permalink

Triacetone Triperoxide is a very unstable organic peroxide and is classed as high primary explosive and when it's atom is disturbed it releases energy and a chain reaction begins and the energy that holds the atom together falls apart and realeses a ery powerful shock wave but it lets no heat just a blast pressure

T.A.T.P. is created when 3 molecules of acetone are reacted with 3 molecules hydrogen peroxide and a strong acid catalyst is used this causes the hyodrogen peroxide to donate 3 oxygen protons to the acetone making C9H1806