How IEDs Work

Anatomy of an IED

Before we pick apart an IED, a refresher on more conventional bombs might be handy.

Landmines are planted within a designated area (a minefield) and are intended to bring down entering soldiers or vehicles.
Soldiers throw hand grenades over a short range to clear an area of enemy personnel.
Rocket-propelled grenades, or just RPGs, are launched over a larger range and can rid a target area of enemy personnel or destroy enemy vehicles.
Bombs are dropped from planes, are self-contained and controlled to devastate anything within a specific area.

Such bombs are commercially made. Armies purchase these weapons from defense contractors for military and training operations, although other individuals can obtain them through the thriving black market for weapons.

In contrast, IEDs are homemade with five basic parts:

A power supply, often provided by car batteries or alkaline flashlight batteries
A trigger, switch or some other direct or indirect means of setting the device off, such as a radio signal, trip wire, timer or firing button that someone presses. A common form of remote trigger is a cell phone, cordless phone, radio or garage door opener activated by someone who is watching [source: GlobalSecurity.org].
A detonator, a small explosive charge that sets off the main charge. Detonators are usually electrical, like those used for explosions in construction.
A main charge, the primary explosive that's the big guns behind the blast. Unexploded landmines fit the bill.
A container to hold everything together. The container may be designed to force the blast in a specific direction.

Additional components packed in the device may include projectiles for shrapnel, such as ball bearings, nails and stones, as well as hazardous, toxic or fire-starting chemicals. IEDs may also be used as the explosive part of a biological or radioactive dirty bomb.

Let's look at how these parts work together:

The power source supplies electricity to the trigger or switch and to the detonator.
The trigger activates the detonator and initiates the explosion sequence. The trigger may sense the target, be activated by the target, be a timed trigger or be operated remotely.
The detonator explodes, thereby providing energy for the main explosive.
The main charge explodes, producing a high-pressure shock wave or blast wave, and may propel shrapnel, toxic chemicals or fire-starting chemicals.

Here's the distressing part: IEDs are relatively simple to make with a little research, time and training. After all, how hard is it to get batteries, cell phones and radios? Detonators and explosives such as C-4, Semtex and dynamite can be found at construction sites and oil rigs. They also may be stolen, purchased legally or cooked up at home or in a makeshift lab. Terrorist groups have been known to post recipes on their Web sites.

Once made, people tend to use one of three methods for delivering their weapon. Often they'll conceal the device in a package that may be in plain sight, hidden or buried. Insurgents have even hidden IEDs in animal carcasses alongside military convoy routes. They may also place the IED in a vehicle's trunk (vehicle-borne IED or VBIED). A driver may park the vehicle alongside a convoy route. A remote watcher can then detonate the VBIED from a safe distance. The last delivery method relies on a suicide bomber. The suicide bomber may drive a VBIED into the target area and explode it or strap the device on his or her body, walk into the intended target area and explode it.

What happens when an IED explodes?