A Primer in PETN

PETN, the explosive that nearly doomed Northwest Airlines Flight 253 in Detroit on Christmas Day, is a white powder that can deliver powerful blasts in quantities as small as tenths or hundredths of a pound.

But generally, it can't be lit with a match or otherwise set off without using a detonator or mixing it with a chemical to cause an explosion.

"It's a high explosive; it's one of the more sensitive things to handle," said Jimmie Carol Oxley, co-director of the Center of Excellence In Explosives Detection, Mitigation, Response and Characterization at the University of Rhode Island, Kingston. "But it doesn't initiate with a flame."

Her view, consistent with initial reports from investigators of the incident, is that Umar Farouk Abdulmutallab, the Nigerian accused of trying to blow up the plane, "was looking for a chemical reaction that would be hot enough to initiate" the PETN and cause it to explode. "It's not impossible, but it's not easy either and it obviously didn't work for him," Prof. Oxley said.

Mr. Abdulmutallab allegedly was carrying a syringe with liquid believed to be an agent he was mixing with PETN to cause it to explode. Unlike a detonator such as a blasting cap, a syringe and PETN are very difficult to detect with X-ray equipment commonly used at airport security checkpoints.

Residue from the powder, though, is easily detectable with swabs that security personnel often use to wipe off briefcases, luggage and other personal items taken through checkpoints. Prof. Oxley has done research indicating PETN residue can be detected in human hair.

"We've been very successful looking at people's hair as evidence that they're handling explosives," she said. "That's not a common screening tool used in the airport."

For more information, read the full story at The Wall Street Journal.