Boston Marathon Bombing Investigation Points Toward Pressure Cooker IED and Acetone Peroxide Type of Explosive

Controlled detonation of a improvised pressure cooker IED.

The FBI has confirmed that pressure cookers may have been used in the Boston Marathon bombings that killed three and wounded more than 170. Apparently an improvised conventional pressure-cooker.

In mid-2010, the Department of Homeland Security put out a circular, “Pressure Cookers as IED Components [PDF]” classified “For Official Use Only,” warning of their potential use in domestic attacks:

Rudimentary improvised explosive devices (IEDs) using pressure cookers to contain the initiator, switch, and explosive charge (typically ammonium nitrate or RDX) frequently have been used in Afghanistan, India, Nepal, and Pakistan. Pressure cookers are common in these countries, and their presence probably would not seem out of place or suspicious to passersby or authorities. Because they are less common in the United States, the presence of a pressure cooker in an unusual location such as a building lobby or busy street corner should be treated as suspicious.

Terrorists can exploit the innocuous appearance of easily transportable items such as pressure cookers to conceal IED components. Placed carefully, such devices provide little or no indication of an impending attack. Alertness and quick reaction to discovery of such concealment
devices in unusual locations or cirumstances can improve chances of early detection and prevention of an attack. Potential indicators of a pressure cooker configured as an IED include:

— (U) Protruding wires or fuses.
— (U) Unusual smells such as chemical odors.
— (U) Wetness or unusual stains on a container.
— (U) Apparent abandonment of a pressure cooker in a high traffic or otherwise strategic location.

The failed Times Square bomber used a similar device. One of the three devices used in the 1 May 2010 attack in Times Square incorporated a pressure cooker containing approximately 120 firecrackers. The devices have also been used in Afghanistan, Pakistan, Nepal, and Malaysia.

The explosives used in the Boston Marathon bombings were likely homemade devices, possibly using acetone peroxide explosive, and were full of nails and metal fragments designed to cause widespread injury. The use of C4 or Semtex is ruled out because those explosive produce more powerful detonations with black smoke. There is speculation that the explosive is an acetone peroxide explosive, which causes white smoke, and is easily obtained from household chemicals.

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