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WASHINGTON – Militant Islamic terrorists for years have been employing IEDs, or improvised explosive devices, against U.S. troops in Iraq and Afghanistan, but now they’re turning increasingly to IID, or improvised incendiary devices, terror experts say in a report in Joseph Farah’s G2 Bulletin.

IIDs, which use flammable gas or liquids to explode in crowds and produce mass casualties, have been a favorite weapon of terrorists overseas, and experts say they also now are becoming a threat in the U.S.

It is hard to detect and prevent such attacks.

According to the Homeland Security Newswire and Global Terrorism Database, terrorists used IEDs in some 207 terrorist plots in the U.S. from 2001 to 2011. The most recent IED attack in the U.S. was the pressure-cooker attack during the April 15 Boston Marathon that killed three people and injured more than 160.

A pressure cooker also was used in the May 1, 2010, attempted vehicle bombing in New York City’s Times Square. While it basically fizzled and was detected soon thereafter, it contained propane, gasoline and fireworks.

One of the best known IIDs is the Molotov cocktail, which consists of gasoline in a bottle with a piece of cloth as a timer and detonator.

“Terrorists are using flammable liquids and gas as a substitute for explosives or as a perceived enhancement to homemade explosive charges if they cannot obtain high explosives because of restrictions on their sale, or where expertise in making HMEs is limited,” according to a report in the open intelligence Langley Intelligence Network Group, or Lignet. “One concern is that the raw materials can be purchased at hardware and camping stores.”

In addition to gasoline, other commonly available flammable materials include propane, since acetylene can be ignited with a spark, kerosene, cigarette and charcoal lighter fluid and diesel.

A little-noticed March 2010 U.S. Department of Homeland Security report, classified as U/FOUO, or Unclassified/For Official Use Only, warned about the potential use of IIDs for terrorist acts especially in the U.S.

The report is titled “Terrorist Use of Improvised Incendiary Devices and Attack Methods.”

“Improvised incendiary devices (IIDs) typically are less expensive to make than improvised explosive devices but still are capable of creating mass casualties and causing widespread fear and panic,” the DHS report said. “IIDs can be used against many types of infrastructure targets; violent extremists have used them successfully in attacks in the United States and overseas.”

The report refers to common materials used to make IIDs. Their availability is so common that their purchase doesn’t draw any attention.

IIDs require little training to prepare and use. Flammable materials generally are not as volatile as explosives and require less skill and expertise in handling.

“For terrorists, seeking to preserve anonymity, IIDs improve prospects for destroying evidence, while those seeking publicity can benefit from the media coverage that a fire will attract,” the DHS report said. “Properly used and strategically placed, IIDs can cause damage over a widespread area as the fuel may rapidly create and sustain a fire that is difficult for first responders to contain.”

Experts warn that IIDs can be particularly devastating in enclosed areas where people crowd together, such as on ramps to board subway trains.

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