Dozens of alleged terrorists were recently arrested in Britain and Pakistan, accused of plotting to blow up as many as ten transatlantic airliners. Police report the terrorist plan was to blow up the planes using suicide bombers armed with liquid chemical bombs smuggled on board disguised as drinks.

All explosives are chemical in nature. Explosives can be a simple physical mixture of an oxidizer and an organic fuel. Many readers are familiar ANFO, a widely used solid commercial explosive composed of ammonium nitrate (the oxidizer) and fuel oil (the organic fuel). ANFO was used in the 1995 attack on the Murrah Building in Oklahoma City.

According to Dan Keenan, a certified Hazardous Materials Instructor for the California Specialized Training Institute and developer of the hazmat technician training course "Fun With Chemistry," explosives that would be well suited for amateur manufacture is Triacetone Triperoxide – commonly referred to as TATP. TATP can be prepared using commercially available materials obtained from hardware and drug stores: acetone (nail polish remover), hydrogen peroxide (a bleaching and cleaning agent) and sulfuric acid. TATP has been used by suicide bombers in the Middle East, and was also used as an improvised detonator by the infamour "shoe bomber" Richard Reid in his failed attempt to blow up an airplane in December, 2001.

Keenan explains that nitrated compounds could also be used to create a homemade explosive. One example would involve taking the common emollient, glycerin, and adding it to a mixture of concentrated nitric and sulfuric acids creating nitroglycerine, a liquid explosive well suited for a terrorist’s aims.

Another possibility, Keenan reports, is the use of antifreeze (ethylene glycol), which when added to a mixture of nitric and sulfuric acid would create an explosive liquid compound called ethylene glycol dinitrate. Similarly, an ingredient in toothpaste, propylene glycol, becomes deadly when added to a mixture of concentrated nitric and sulfuric acids creating the liquid explosive called metriol trinitrate, which is similar to nitroglycerine.

Once the terrorists have the explosive, Keenan says, they would still need a detonating agent. Terrorists could possibly detonate the homemade liquid explosives without the need for a blasting cap by introducing a simple electric circuit, employing a 9-volt battery or the battery pack from a laptop computer. A toothpaste explosive could even be ignited by a match; but to insure complete detonation an explosive train involving a primary explosive, or a booster like the TATP mentioned above would be needed.

Prime location
In order for an explosion of one of these compounds to succeed in taking down an airplane, Keenan thinks, it would have to take place near the skin of the airplane; in other words, right next to the side, and preferably the window – close enough to blow a hole in the side or to blow out the window. The first reported act of sabotage against an airplane took place in 1933 over Chesterton, Indiana and involved a nitroglycerine bomb planted in the tail assembly of a Boeing 247 and detonated by a timing device. The 10 people aboard were all killed.

How much of the explosive compound would be needed to blow a hole in an airplane? Keenan believes that about eight ounces would be adequate. Richard Reid had eight ounces of TATP in his shoe, which probably could have blown out the side of the plane, or at least a window.

In Keenan’s opinion, it would be difficult to bring down an airplane with this type of explosive in checked luggage because of the location of the baggage compartment. A terrorist would need a lot more product to effect an explosion that would be large enough to guarantee a hole in the aircraft, and would have no guarantee when or where – or if – the explosion would take place.

"Mother of Satan"
TATP is one of the most sensitive explosives known, susceptible to impact, temperature change, and friction. For this reason, it has been called the "Mother of Satan." This characteristic is what makes TATP intriguing to terrorists, but at the same time causes it to be exceedingly difficult to work with.

Although officials have declined to discuss the technology planned for the thwarted plot, one scenario is that multiple terrorists would board a plane, each armed with one element of a bomb, which by itself would be innocuous. During the flight, the terrorists would manage to gather the products, mix them together to cause a volatile product, and detonate that mix using an electronic device. Keenan questions the validity of this scenario. "I seriously doubt that any of these compounds could actually be successfully synthesized on an aircraft. The concentrated acids required, the time and temperature control involved, make that scenario highly unlikely."

Detecting chemical explosives
There are a few technologies out there that can detect liquid chemical explosives. The primary one in use is ion mobility spectrometry (IMS). IMS is based on the principle that when differently charged molecules (ions) are acceleterated through an electric field, they will travel at different speeds and reach a detector at different times. At airports, IMS may be implemented in different ways to look for trace amounts of explosive compounds. In one system, a person would walk into a chamber where puffs of air are blown at him or her. The air is then analyzed for trace ions of explosives. A different system has agents using a swab to sample a person’s hands and carry-on luggage. The swab is tested in a machine where it is heated to create vapors that are ionized. The ions are pulled into a machine where they are measured for trace ions of explosives. While this technology is designed to detect finished explosives it is questionable whether it would identify the pre-cursors suggested by this plot.

Another technology known as Raman spectroscopy illuminates the substance with an extremely bright invisible laser light, exciting some of the molecules and causing characteristic wavelength-shift in laser light scattered from the molecules. The scattered light is specific to each molecular type, and thus serves as a unique fingerprint of the mixture and blend of material being tested. One manufacturer, Ahura Corp., manufactures Raman-based equipment that is portable, can identify liquids and solids in their containers and is increasingly being used in the field by first responders.

Be vigilant, be suspicious
When asked what security officials need to know about chemical explosives, Keenan was thoughtful. "I have to say that it is important for security officials to rely less on technology, and more on hunches and instinct." He cautions against believing everything that is published, and especially against believing what is on the Internet. He points to the potential scenario that has been widely published of terrorists mixing explosives in the bathrooms of aircraft. "There is a lot of false information out there. Get your information from experts in the explosives field."

And for security officials, emergency responders, and citizens alike, he has this message: "I think the message is ‘be ever vigilant. And if you’re not the person sitting next to the window, be suspicious of the person who is."

Dan Keenan has been a firefighter and HazMat responder for the City of Oakland (CA) Fire Services Agency since 1991.He is certified by CSTI (California Specialized Training Institute) as a Hazardous Materials Instructor. Dan felt a need to promote hazardous materials training with the use of live chemical demonstrations, and this interest fueled the development of "Fun with Chemistry," which he presents to emergency responders. Dan’s chemical demonstrations has been featured in Emergency Film Group's Hazmat Operations," "Introduction to Hazardous Chemicals," and "Fun With Chemistry." Dan received the California State Fire Marshal's "Instructor of the Year" Award in 1999.