Pressure cookers are common household appliances found in many kitchens around the world and used for a range of purposes from cooking rice to preserving food in cans. But by filling one with explosives, small pieces of metal and a triggering mechanism, it is possible to make a deadly improvised explosive device similar to those authorities believe were used in the attack on the Boston Marathon.
WHO USES THEM?
U.S. officials have long warned that pressure cookers can be used in terrorist attacks. In a 2004 memo, the U.S. Department of Homeland Security reported that the conversion of pressure cookers into IEDs was a technique commonly taught in Afghan terrorist training camps.
An issue of Inspire - an online magazine tied to al-Qaida and the late U.S.-born radical cleric Anwar al-Awlaki - included an article entitled "How to Make a Bomb in the Kitchen of Your Mom," which instructed would-be bombers on how to use a pressure cooker in an attack.
In addition, anarchist websites and white supremacist groups have discussed the use of pressure-cooker bombs.
In 2011, U.S. Army Private Naser Jason Abdo was charged with plotting to blow up fellow troops, and authorities found pressure cookers and smokeless gunpowder in his motel room. The failed 2010 vehicle bomb in New York's Time Square was a pressure-cooker device containing 120 firecrackers. Also that year, a suicide bomber in Stockholm had rigged a pressure-cooker bomb that failed to detonate.
Such bombs have been extremely popular in attacks in South Asia. The chief of the bomb disposal squad in Pakistan's Khyber-Pakhtunkhwa province - a region racked by militant attacks on civilians - told the LA Times newspaper that roughly half of the more than 5,000 explosive devices that have been defused since 2009 have used pressure cookers.
U.S. officials warned that this type of bomb does not require much money or special training to make. They also can look innocuous to the untrained eye.
But a drawback for attackers is that the blast radius of a pressure-cooker bomb is reduced because of the significant energy needed to break through the cooker's thick steel walls. At the same time, parts of those steel walls can become projectiles, compounding the lethality of the devices.