Liquid Explosives

Two prospective terrorist attacks - a foiled plot in 1995 in Manila to bomb airliners crossing the Pacific and a foiled plan in 2006 in London to bomb trans-Atlantic flights - focused a spotlight on liquid explosives as a threat to aviation. Such weapons are regarded by authorities as extremely difficult to detect by methods currently in place-basic X-rays of carry-on baggage.

Liquid explosives essentially depend on a two-step process: first, a combination of chemicals which, while inert by themselves, create a highly explosive compound; second, detonation of the compound by a low-level electrical spark, such as might be generated by a personal music player or other electronic device. The separate ingredients of such a compound can be obtained over the counter and combined by a suicidal terrorist aboard a plane. Authorities say the combined ingredients can easily be disguised as benign substances, for example, by using dyes.

A major concern is that even a relatively small explosion from a small quantity of chemicals could start a fire that could, in turn, burn through a plane's relatively thin aluminum skin, causing the plane to crash.

The Chemistry

Although liquid explosives are much less common than solids, there are several types of liquid explosives that lend themselves to manufacture by terrorists relying on ingredients easily obtained by consumers. Recipes of varying degrees of detail are readily available on the Internet.

In some cases, the liquid explosives are created by mixing two otherwise innocuous substances together. One expert compared the process to that of mixing a gin and tonic drink. The resulting mixture can become highly explosive very quickly and can be easily set off by an ordinary consumer electronic device such as a wristwatch or music player. It was for this reason that British authorities banned carrying on all such objects in the immediate aftermath of uncovering the August 2006 plot.

Among the liquid explosives of concern to anti-terrorism officials are:

Triacetone triperoxide (TATP). British security officials were quoted anonymously as saying this explosive was intended to be used in the plot to bomb transatlantic airliners that was thwarted in August 2006. TATP was associated with earlier plots by al Qaeda and has been used by Palestinian terrorists. It is made from two liquids-acetone, an ingredient in nail polish removers, and hydrogen peroxide, an ingredient in over-the-counter household antiseptic solutions (in a highly diluted form). It is sometimes used as a bleaching agent or as a medical antiseptic. Although hydrogen peroxide in a solution sufficiently strong to serve as an ingredient in an explosive is not readily available, reduction of it to a usable level is well within the means of a dedicated terrorist. Experts say that even a diluted form could set off a fire that could burn a hole through the thin aluminum skin of aircraft, causing rapid depressurization and a crash.

Nitromethane (CH3NO2). Associated with some forms of auto racing, nitromethane can be used as a substitute for gasoline. In an automobile cylinder, nitromethane delivers more explosive power than a comparable volume of gasoline.

Nitroglycerine (C3N3H5O9). First discovered in 1846, nitroglycerine is the compound usually associated with dynamite. In its liquid state, the substance is highly combustible - it can explode when exposed to a small electrical spark or even to violent jiggling. Nitroglycerine freezes at a relatively high temperature, however, and is often cooled to around 5 to 10 degrees Celsius (40 to 50 degrees Fahrenheit), at which point nitroglycerine is much more stable.

Ammonium nitrate (NH4NO3) is well known as a home-brewed explosive. It is made by combining ammonium nitrate with fuel oil, which creates a mixture called "ammonium nitrate fuel oil (ANFO)," which has the consistency of toothpaste. Simply mixing over-the-counter fertilizer and fuel oil does not make an effective explosive; this requires adding other ingredients that are well within reach of dedicated terrorists.

Terrorism and Liquid Explosives

The alleged plot foiled by British authorities on August 10, 2006, was by no means the first time that terrorists had planned to use liquid explosives to bring down trans-oceanic airliners.

On January 13, 1987, Lebanese citizen Mohammed Hammadi, accused of hijacking a TWA plane in Athens in 1985, was arrested at the Frankfurt airport after security agents discovered liquid explosives in his luggage. Hammadi, whose family was active in Hezbollah, was released in December 2005, well before serving out his sentence on the explosives charge, and to the consternation of US officials.

An earlier plot, code-named Bojinka (a Serbo-Croatian word meaning "big bang"), was thwarted by a fire in a Manila apartment where terrorists led by convicted al Qaeda terrorist Ramzi Ahmed Yousef, the convicted mastermind of the first effort to destroy the World Trade Center in 1991, were preparing materials for an attack. In 1995, Yousef was in Manila, mixing chemicals that he planned to put onto airliners destined to fly across the Pacific bound for the United States. The plan was to put the chemicals in containers with timing devices. The plotters would then leave the plane at some intermediate stop, leaving the bomb behind on the aircraft. Practice bombs placed in a Manila theater in late 1994 and on a plane flying from Manila to Tokyo both went off as planned. But a fire in the Manila apartment where the terrorists were working led police to a laptop computer owned by Yousef. The plot was foiled, and Yousef fled to Pakistan, where he was later arrested and turned over to the United States. He is now serving a life term in prison.

The Manila plot was said to involve a stabilized form of nitroglycerine carried aboard in a bottle made to look like a contact lens solution. Officials observed that by planting the seemingly innocent substances on planes and then getting off before the plane took off on another leg bound for the United States, the hijackers would not have had to obtain US entry visas and would have seemed to be flying only between two other countries.

In December 1999, Ahmed Ressam, the so-called Millenium Bomber, was arrested entering the United States from Canada. Authorities found a can of nitroglycerin in his car that Ressam intended to use to set of a series explosions at the Los Angeles airport in conjunction with the millennium. Ressam was sentenced to twenty-two years in prison.

In March 2004, police in Islamabad, Pakistan, found and disarmed a Suzuki van carrying 200 pounds of liquid explosive two days before a scheduled visit by then-Secretary of State Colin Powell.

Detection and Prevention

Detecting liquid explosives is not impossible, but in 2006 there was no way of doing so that was not too time-consuming to be considered feasible for everyday use at airports. In the years since, scientists have created machines that effectively detect explosives, and airports have installed them globally. Though the amount of liquids allowed per passenger remained limited in 2023, the advent of the technology promised an end to those restrictions was on the horizon.

Much more attention (and spending) has been paid to using X-ray scanners to detect more conventional weapons, such as handguns, and to hiring and training human screeners. In fact, funding to develop a detection system for liquid explosives was actually cut in 2003, according to Congressional testimony in 2005 by the director of the Government Accountability Office's Homeland Security and Justice division.

One early technology, so-called "puffer" machines that blow a whiff of air onto passengers to detect recent exposure to chemicals used in explosives, was intended to be installed in about thirty US airports. But this technology was limited. If a passenger had taken precautions in handling the explosive (or has never personally handled it), the puffers were ineffective.

Consequently, the solution adopted in the United States and Britain was to ban all liquids or gels carried aboard by passengers, with a very short list of exceptions (baby formula, for example). Britain adopted even more stringent regulations in light of the plot. There, passengers were barred from carrying any items of hand baggage, electrical equipment, or liquids on planes. Those restrictions were amended to the rules limiting the amounts passengers could carry. By the 2020s, the technology had been developed and installed in airports that could reliably detect whether a liquid was benign or dangerous; however, restrictions remained in place.

Bibliography

"Aviation Security: Challenges Exist in Stabilizing and Enhancing Passenger and Baggage Screening Operations," Government Accounting Office, GAO Reports; 2/12/2004, p. 1.

Barrows, Matthew. "Federal Contracts Spur Creation of Sophisticated Detection Devices," Sacramento Bee, 11/30/2001.

Black, Jane. "El Al's Security Vs. the U.S. Approach," Business Week Online; 8/25/2003.

Grier, Peter and Ron Scherer. "High-tech bombs foil best detection efforts," Christian Science Monitor; 7/25/96, Vol. 88 Issue 168, p. 1.

McLaughlin, Abraham. "In push for security, 'convenience' prevails," Christian Science Monitor, 1/18/2002, Vol. 94 Issue 39, p.2.

Peritz, A. (2022, Jan. 2). How the U.S., U.K. and Pakistan teamed up to stop another 9/11. Politico. Retrieved Oct. 4, 2023, from https://www.politico.com/news/magazine/2022/01/02/liquid-bomber-plot-counterterrorism-international-cooperation-526246