How Controlled Detonations Work

Neutralizing the Risk: Controlled Detonation and Disruption

The most straightforward approach to controlled detonation is to destroy the bomb without moving it. If it's located in a populated area, the bomb squad may choose to place protective works -- sandbags or blocks -- around the device to mitigate the blast effects. Otherwise, they can neutralize it right where it sits. This almost always involves a robot, which carries C-4 to the device and, using its manipulator, attaches the plastic explosive to it. After the machine trundles away, the remote operator detonates the C-4, which causes the bomb to explode. In many ways, the C-4 becomes the initiator, but in EOD jargon, it's known as a countercharge [sources: Anderson, Kelley].

Another option is to disrupt the device so it can be moved to a lab for further analysis or a detonation range for destruction. Bomb technicians often target electronic switches because they can be damaged by predetonators, which emit powerful electronic pulses that fry integrated circuits. In such a situation, the device can "fail open" -- which means it won't explode -- or "fail closed" -- which means it will explode.

Because of this uncertainty, bomb technicians sometimes turn to another class of disrupters that function like small cannons, firing a jet of high-pressure water or specialized ammunition to break apart a bomb's components. Many different models exist, but they all have a similar design. They're usually small, mount on a tripod and have a laser sighting system so the disrupting blast can target a very specific part of the device. A bomb tech or robot must place the disrupter near the device, but once it's been set up, it can be fired remotely.

After disrupting an unexploded bomb or IED, disposal teams can move the device to a remote location. Sometimes, they place the explosive in a containment vessel to protect handlers and the public from an inadvertent blast during transport. This round, steel ball measures up to 12 inches (0.3 meters) thick and can withstand the blast of approximately 10 pounds (4.5 kilograms) of explosives [source: FBI]. Newer models are completely automated and work closely with robots. After receiving a disrupted device, the system can seal itself without any human intervention. Then it's off to a detonation range, where the explosives are removed and neutralized. Controlled detonations at a range resemble those conducted at the original site of a bomb. Technicians often use C-4 to blow up unexploded ordnance or an IED. If they're dealing with small arms ammunition, however, they may use gasoline, kerosene or thermite, a mixture of finely powdered aluminum and iron oxide that burns at a very high temperature, to dispose of the explosives.

Still, controlled detonations can never be completely controlled, which is why bomb disposal remains one of the deadliest occupations. Perhaps one day better tools and techniques will come along to replace the methods used today. Until then, blowing stuff up may be the best way to thwart the folks who want to blow us up.

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