In the kitchen, pressure cookers use an airtight lid to trap the steam, which raises its cooking temperature to about 250 degrees Fahrenheit (121 degrees Celsius) — ideal for quickly cooking vegetables, meats or soup.
The devices can vary by brand and model, but all pressure cookers generally have the same three components: a pressure regulator, to control and maintain pressure inside the cooker; a vent pipe, which allows excess pressure to be released; and a sealing ring, which creates a pressure-tight seal between the lid and the body.
These otherwise benign appliances are somewhat easy to transform into deadly weapons.
A look at the pressure cooker recovered on 27th St. four blocks from the #Chelsea explosion https://t.co/nf10q2dRw9 pic.twitter.com/m82QDVsLjN— New York Daily News (@NYDailyNews) September 18, 2016
Instead of food, explosive materials such as TNT and dynamite are placed inside the pressure cooker. Next, nails, ball bearings or other shrapnel surround the explosive materials.
Using other common devices, such as digital watches, garage door openers or cell phones, a would-be bomber can remotely trigger an electrical charge, which in turn ignites the pressure cooker’s explosive contents.
The ignition quickly expands until it blows open the cooker, spitting out shrapnel with the speed and force of bullets.
“The size of the blast depends on the size of the pressure cooker and the amount of explosive placed inside,” according to the Homeland Security bulletin. Pressure cooker bombs “can be as simple or as complex as the builder decides.”
In a 2010 memo, Homeland Security said such rudimentary devices were used frequently in Afghanistan, India, Nepal, and Pakistan, and occasionally in the United States and Europe. A failed 2010 bombing attempt in New York City’s Times Square, for instance, involved a pressure cooker stuffed with 120 firecrackers.
Three years ago in Boston, brothers Dzhokhar Tsarnaev and Tamerlan Tsarnaev planted pressure cookers filled with shrapnel near the Boston Marathon finish line.
The explosions killed three people and injured at least 264 others.
George Velmahos, chief of trauma surgery at Massachusetts General Hospital, said all of the victims had “10, 20, 30, 40 pieces of shrapnel embedded in their bodies, mostly in their legs, but as high up as their necks,” USA Today reported at the time.