Liquid explosives of the sort suspected in an alleged plot to blow up airliners are easy to make and difficult to detect by airport security systems, according to explosives experts.
While the exact ingredients of the bombs remained murky, experts said yesterday that hundreds of chemicals could be combined to make explosives capable of bringing down a commercial jet. Some of those chemicals can be found in common household products.
Bomb-making ingredients are so easy to obtain, in fact, that some explosives experts were reluctant to provide too much detail or to even discuss the matter. Others, however, acknowledged that finding information on constructing bombs is disturbingly easy.
"I'm sure the bad guys know how to do that," said Sam A. Kiger, a professor at the University of Missouri, Columbia.
Kiger, an expert on building explosive-resistant structures, and others theorized that the plotters chose liquid explosives because they can be difficult to distinguish from fluids passengers often carry onto airplanes - drinks, shampoo and contact lens solution.
Another advantage for bomb-makers is that airport screening devices look only for traces of solid explosives, experts said.
A peroxide-based explosive was used in the July 2005 London subway bombing. Planted on three subways and a double-decker bus, the bombs killed 56 people and wounded more than 700. British investigators found two unexploded devices containing HMTP, or hexamethylene triperoxide diamine peroxide. The main ingredient in the homemade devices, hydrogen peroxide, is found in hair bleach and antiseptic.
Kiger said a chemical he uses in his research, nitromethane, looks like water and is fairly stable when pure. But combining nitromethane with other compounds can turn it into an explosive more powerful by weight than TNT. It was used in the bomb that destroyed the Alfred P. Murrah Federal Building in Oklahoma City in 1995.
"As a minimum, it would blow a hole in the side of the plane, and would certainly kill people within 10 or 12 feet," Kiger said.
The chemical is also the primary ingredient in PLX, or Picatinny liquid explosive, which was developed at the U.S. Army's Picatinny Arsenal in New Jersey during World War II.
"You can find the recipe on the Internet if you look," said David Williams, a retired FBI forensic explosives expert. "If you had a pint of it inside a car with the doors and windows closed, it would blow the doors off."
PLX is thought to be one of the explosives responsible for bringing down Korean Air Flight 858 in 1987. The Boeing 707 exploded over the Andaman Sea en route from Baghdad to Seoul, killing the crew and all 115 passengers.
A suspected North Korean agent involved in the plot later told government authorities that the PLX was in a whiskey bottle. The terrorists also planted 350 grams of the plastic C4, a solid explosive, inside a Panasonic radio rigged as a time bomb on the plane.
Another solid explosive favored by terrorists is triacetone triperoxide. Experts say TATP can be easily cooked up in a basement lab because the two main ingredients can be purchased in pharmacies and hardware stores.
TATP was packed into the black suede sneakers worn by convicted "shoe bomber" Richard Reid, who in December 2001 attempted to bring down American Airlines Flight 63 from Paris to Miami.
Reid was stopped when a flight attendant noticed him attempting to light his shoe with a match. Investigators later discovered that the shoe contained TATP and 4 ounces of penthrite, a powerful military-grade explosive. Although relatively easy to make, TATP is dangerously sensitive to temperature, pressure and friction.
"You won't find anybody making TATP except the crazy guys in the FBI lab who have to make it," said Christopher Ronay, a former head of the FBI explosives unit who now heads the Institute of Makers of Explosives. Last month, a 21-year-old man was killed while trying to create TATP in his apartment near Houston.
Another powerful liquid explosive often concocted by laymen is nitroglycerine. Experts said it can be made from three easily obtainable ingredients: nitric acid, sulfuric acid and glycerin. "You could walk into CVS and buy glycerin," said Ronay. The result is a viscous, colorless to pale-yellow liquid that would be easily mistaken for shampoo, experts said.
But nitroglycerine can also be finicky, said Jimmie C. Oxley, a chemist and explosives expert at the University of Rhode Island.
She said nitroglycerine is so reactive that, had the would-be bombers in Britain tried to use it, they might have blown themselves up before they reached the airport. Instead, she suggested, the conspirators might have planned to use a more stable liquid, one that would require some kind of detonating device. According to authorities, detonators were part of the scheme.
Oxley said the detonators would be hard for airport security personnel to detect. "It's just a little aluminum sleeve that is about the size of a cigarette," she said. "It wouldn't look like a threat."
She said explosives detectors in airports do not screen for liquid explosives because terror groups have historically used solid explosives such as C4 and TATP.
"Now we will probably get some new detection equipment in the airports," she said, "and people will get to carry their shampoo again."