By KENNETH CHANG
Published: October 30, 2010
Pentaerythritol tetranitrate, or PETN, the explosive found in two bombs hidden in printer cartridges that were being shipped via jets from Yemen to the United States, is a hallmark of earlier Qaeda-linked terrorism attempts on airplanes.
In 2001, PETN was found hidden in the shoes of Richard C. Reid during an American Airlines flight. Last Christmas, Umar Farouk Abdulmutallab had three ounces of PETN hidden in his underwear on a Northwest flight from Amsterdam to Detroit.
An assassination attempt in August 2009 on Saudi Arabia’s intelligence chief, Prince Mohammed bin Nayef, also employed PETN. Al Qaeda in the Arabian Peninsula, an arm of the terrorist network, claimed responsibility for the attack, which took the life of only one person, the suicide bomber’s.
But other terrorist groups have also used PETN, and the presence of the explosive itself does not decisively point to Al Qaeda. “That’s a very common explosive,” said Jimmie C. Oxley, a professor of chemistry at the University of Rhode Island. “There’s no reason to think a lot of people didn’t have access to do that.”
PETN, a white powder that was introduced after World War I, belongs to the same chemical family as nitroglycerin. It is about 70 percent more powerful than T.N.T., and is stable. PETN generally does not explode when dropped or set on fire. Usually, a strong shock wave from a blasting cap or an exploding wire detonator is needed to set it off.
Those properties make it well suited for a variety of commercial applications. PETN is a major ingredient of the plastic explosive Semtex and is used in detonation cables.
For terrorists, PETN is an attractive choice for package bombs. Its stability means it is unlikely to explode prematurely, but at its destination, it will go off with deadly force when detonated. (Conversely, the stability of PETN also thwarted the attacks of Mr. Reid and Mr. Abdulmutallab, who were not able to detonate their explosives.)
Dubai officials said that the printer cartridge bomb intercepted there on Friday included lead azide, an explosive to detonate the PETN, and a cellphone circuit, presumably to allow the bomb to be set off remotely. Neal Langerman, president of Advanced Chemical Safety, a consulting firm in San Diego, said it appeared “to be a fairly sophisticated device.”
Judging from photos of the Dubai bomb, Dr. Oxley estimated that the printer cartridge contained about two pounds of PETN.
The British home secretary, Theresa May, said Saturday that the second bomb, intercepted in Britain on Friday, contained enough explosive to bring down a plane.
The target of the bombs remains unclear; they could have been directed at the synagogues or Jewish community centers in Chicago to which they were addressed.
Placement of a bomb in a plane can be as important as its size in determining the amount of damage it could cause, Dr. Oxley said. While the printer cartridge contained more PETN than Mr. Reid’s shoes or Mr. Abdulmutallab’s underwear, the bomb maker could not be certain where in the airplane the package would be located. Mr. Reid and Mr. Abdulmutallab tried to detonate their devices close to the wall of the respective planes on which they were flying, to increase chances that the explosion would blow a hole in the aircraft.
“Last year, the guy had more control,” Dr. Oxley said, referring to Mr. Abdulmutallab. But the printer cartridge bomb, she said, had so much more PETN that “my guess, and this is only a guess, it may have had a higher probability” of taking down an airplane.
Dr. Langerman said it was curious that the two most recently intercepted devices apparently were different in design. That may indicate that the explosive makers had different targets in mind.
A version of this article appeared in print on October 31, 2010, on page A12 of the New York edition.
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