How IEDs Work

IED Impacts

Aside from how it's made, an IED is like any other bomb -- it explodes. Before you can understand the impact of an IED, it helps to know what's happening during that fateful moment.

When the primary charge explodes, gases heat up and expand rapidly outward under pressure.
The expansion creates shock waves or blast waves. The waves travel outward at about 1,600 feet per second (488 meters per second) over hundreds of yards or more depending upon the amount of explosive.
The explosion fragments the container and sends pieces of shrapnel at high speeds outward. If the IED also contained other fragments such as ball bearings, nuts, bolts and pellets, then they also would be thrown outward.
The heat from the explosion causes fire.
The heat and fires from the explosion can cause secondary fires.
The blast wave leaves a partial vacuum, which causes air to rush back in under high pressure. The inrushing air also pulls in debris and shrapnel.

So, an IED explosion causes damage to vehicles and property primarily through the blast wave, heat and fires.

In contrast, casualties within the blast radius can stem from many causes. The explosion can release shrapnel or create debris from secondary impacts such as flying glass from broken windows. This debris can penetrate the body in many places, leading to lacerations, bleeding, broken bones and loss of limbs. Second, the heat from the blast causes fires; both the heat and the fires themselves can cause severe burns. Finally, the pressure in a blast wave can be on the order of 1,000 times atmospheric pressure. This intense pressure can rupture your eardrums and slam your brain against the inside of your skull, which leads to concussion, blindness, deafness and swelling of the brain. In addition, many air-filled tissues and organs such as the lungs and bowels can be perforated by the pressure changes.

The type and extent of the injury depends on the person's location relative to the IED. A person in the primary blast radius can be hit by pressure changes, heat and shrapnel. Most likely, this person will die. Outside the primary blast radius, a person is most likely to be injured by shrapnel. The person may survive depending on how many injuries the shrapnel causes and where they're located. If shrapnel tears a hole in a major artery, then that person can bleed to death.

Civilian casualties are often high in IED attacks because these people are unprotected. Initial injuries to U.S. soldiers from IED attacks were caused mainly by shrapnel. However, the use of Kevlar body armor and helmets has greatly reduced shrapnel injuries. While these types of injuries have fallen, military surgeons have reported increases in traumatic brain injuries caused by the blast effects [source: Okie].