A French soldier watches a controlled explosion of a homemade (artisanal) bomb and other munitions by a bomb-disposal expert on Feb. 14, 2013. The French army found the bomb in northern Mali.

Pascal Guyot/AFP/Getty Images

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Introduction to How Controlled Detonations Work

In Europe, World War II ended on May 8, 1945. The horror of the Blitz and other massive bombing campaigns, however, continues to haunt people in Berlin, London and elsewhere today.

A typical scenario goes like this: During a commercial construction project, workers uncover a bomb that failed to explode when it fell from the belly of an enemy plane decades earlier. Even though the dud seems inert and harmless, it's not. Depending on the bomb's size and construction, government officials may evacuate several blocks, or several square miles, in case the unexploded ordnance decides to, well, explode. (Ordnance is a general term for military supplies that covers things like ammunition and weapons.) In November 2011, the city of Koblenz, Germany, evacuated 45,000 people when a 4,000-pound (1,814-kilogram) British bomb was discovered in the Rhine River [source: Curry].

But getting people out of harm's way is just the beginning. Next, bomb squads must evaluate the device and decide what to do with it. Sometimes, they defuse the bomb, move it to a safe location and then detonate it. Other times, they blow it up where it rests.

These scenarios are more common than you might think. In Berlin, more than 2,000 explosives have been recovered since the end of World War II, but experts believe that as many as 4,000 more remain to be discovered [source: Curry]. And in British cities such as London, Manchester and Plymouth, construction companies use maps to identify the approximately 21,000 locations where there could be unexploded ordnance dropped by the German Luftwaffe [source: Copping]. Did you know that 200 such devices could be lurking beneath the London Olympic Park, site of the 2012 Summer Games [source: Copping]? Or that construction had to be halted after a 2,200-pound (1,000-kilogram) unexploded bomb was found at the site [source: Copping]?

Then there are modern horrors, such as improvised explosive devices, or IEDs, in Afghanistan, as well as pipe bombs, pressure-cooker bombs, car bombs and suicide bomber vests. All of these weapons, if bystanders or surveillance crews are lucky enough to discover them before they explode, must be rendered safe or interrupted before they detonate unexpectedly and without necessary preparations. You might think the most successful disposal procedures produce no explosion at all, but in reality, many call for carefully planned and intentional explosions -- what experts call controlled detonations.

Only highly trained bomb squad technicians in civilian law enforcement agencies, or explosive ordnance disposal personnel in the military, conduct controlled detonations. It's a delicate, hair-raising business that usually ends in triumph, but can, in certain circumstances, end in tragedy.

Let's enter that world now to understand the strange and oxymoronic event known as a controlled detonation.

A member of a U.S. Army Explosive Ordnance Disposal (EOD) team stands at the entrance to a container before an exercise in Kandahar City, Afghanistan, on June 15, 2010.

Ed Jones/AFP/Getty Images

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The Dangerous Business of Detecting Explosive Devices

Unexploded ordnance, or UXO, didn't emerge as a serious problem until World War II. Those bombs turning up in Berlin and London today began as delayed-explosion bombs dropped from Allied and Axis planes between 1940 and 1945. Here's how it worked: Some bombs exploded on impact. Others carried timers so that they would detonate several minutes or hours after hitting the ground -- after soldiers ventured from their hiding places. The clockwork mechanisms frequently jammed, so that the devices remained in their craters or in rivers, lakes and ponds, still packed with deadly explosives. Suddenly, unexploded ordnance was a serious problem demanding a new kind of expert.

In America, the military first took a fragmented approach to developing explosives expertise. Beginning in 1941, the Army managed its bomb disposal operations and training from the Aberdeen Proving Ground in Maryland. The Navy's program was headquartered at the Naval Gun Factory in Washington, D.C. In 1947, responsibility for all explosive ordnance disposal, or EOD, was given to the Navy. By the 1950s, the unique skills of EOD specialists were in high demand nationally and internationally. To better train bomb techs and equip them to deal with increasingly sophisticated and varied threats, the Navy moved its EOD training to Florida's Eglin Air Force Base in 1985.

Today, all military bomb disposal operations are centralized at Eglin, and bomb squads are deployed to support U.S. troops around the globe. In Afghanistan, for example, EOD specialists actively hunt for IEDs left by insurgents, blazing a trail for soldiers to follow. Kathryn Bigelow directed a fictional account of one such solider and his dangerous work in 2009's "The Hurt Locker."

In addition to metal detectors, electronic jammers and other old-school tools, these specialists use a number of new technologies to detect buried explosives. These include the Minotaur, a remote-controlled front-end loader with a nose for pressure-sensitive bombs, and line charges, long ropes studded with small explosives that can blast a narrow footpath and reveal tripwires and other hidden threats. Many EOD teams also cruise the rugged terrain in mine-resistant ambush protected (MRAP) vehicles, armored trucks designed to shield occupants from the shrapnel and shock wave of an accidentally tripped IED.

In nonmilitary situations, it's impractical to actively hunt for threats. Most discoveries of unexploded ordnance come from construction crews during excavation, homeowners who find an old stash of ammunition or fireworks or, in the case of explosives left by terrorists, vigilant civilians. When such a discovery is made, public safety bomb squads, or hazardous devices teams, typically respond. In the U.S., although these teams may be located in state or local law enforcement agencies, they generally receive their training from the FBI, which offers a national accreditation program. Every FBI field office also contains at least one special agent bomb technician, who has received extensive training at the FBI's hazardous devices school located in Huntsville, Ala., at Redstone Arsenal.

A police officer handles a defused improvised explosive device that was found in a public bus in Nairobi, Kenya on March 31, 2013. The IED was ready for detonation when the 25-sitter mini-bus crew discovered it wrapped in a bag, witnesses said.

© Thomas Mukoya/Reuters/Corbis

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Of Duds and Destruction: Potential Threats

Today, EOD specialists face an enormous variety of threats. Bomb makers build their weapons in every size and shape imaginable and experiment with a multitude of designs and explosives. Disposal teams must be able to recognize -- and remember -- a vast amount of information so they can evaluate and neutralize a device before it explodes. To get a feel for the type of threats an EOD specialist faces, it helps to take a crash course in bomb basics.

An explosive is any device that produces a rapid and violent expansion of gases. Chemical explosives allow a combustible material to mix with oxygen in a confined space and in an extremely brief period. This combustible material comes in two basic flavors -- detonating, or high, explosives and deflagrating explosives. Trinitrotoluene (TNT) and nitroglycerine are examples of high explosives. They decompose violently and produce huge amounts of pressure. Black powder is the classic deflagrating explosive. It doesn't explode but combusts rapidly, producing relatively low pressure.

Bomb experts further classify high explosives according to the ease with which they react chemically.

  • Primary explosives detonate when subjected to a spark, flame or impact. As a result, they are very unstable and must be handled carefully. Mercury fulminate, lead azide and diazodinitrophenol (DDNP) fall into this primary category.
  • Secondary explosives require a blasting cap or other initiator to trigger the chemical reaction. Examples include TNT, nitroglycerine and composition 4 (C-4).
  • Tertiary explosives -- the most stable -- won't explode unless a smaller initiating explosion occurs first. Ammonium nitrate (fertilizer) is one example.

As you can imagine, how a bomb maker assembles these explosives can vary wildly. A skilled worker who builds a bomb in a controlled environment according to tight specifications, usually for military applications, produces ordnance, or munitions. People who build one-off bombs in their basement, sometimes simply and sloppily, produce improvised exploding devices, also known as IEDs. IEDs are particularly dangerous, not because they contain high explosives, but because they take so many different forms. They also usually contain ball bearings, screws or nails to inflict maximum damage as they ride the blast's shock wave. IEDs can be packed into cars, briefcases, backpacks, pressure cookers and pipes, all of which can be easily transported and inconspicuously placed.

Bomb disposal teams must deal with any and all of these threats at a moment's notice. One day, they might receive a call about a suspicious vehicle parked next to a government building. The next they may be heading to the airport to investigate a suspicious bag. Even old fireworks and ammunition can be a serious threat if they aren't disposed of properly. Luckily, bomb technicians can do some of their work at a safe distance.

The SAPBER system features an end-cap cutter/remover, collection trays, remote viewing cameras and communications gear – all in the name of making the public safer.

Image courtesy Department of Homeland Security/First Responder.gov

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Remote and Robotic: Evaluating Bomb Risk

There are two versions of what happens when a bomb disposal team arrives at the scene of a suspected explosive device. In the Hollywood version, bomb technicians don their suits and start making their way toward the device -- what insiders call "the long walk." In reality, bomb disposal specialists are way too smart to put themselves in harm's way so readily. Hands-on intervention is a last resort.

Almost all modern bomb squads rely on robots to get their first good look at a threat. Think Wall-E, with tank tracks for propulsion and pincer-like appendages for gripping. Some are small enough to squeeze into a backpack. Others must ride in another vehicle, such as a purpose-built bomb truck. All are capable of navigating different types of terrain and climbing stairs. Some robots, such as the Semi Autonomous Pipe Bomb End-cap Remover (SAPBER), focus specifically on dismantling bombs. Most, however, can investigate threats and, if necessary, neutralize them.

The iRobot 510 PackBot serves as a good example of a modern EOD robot. It's small, lightweight and can move at a top speed of about 6 miles (9.7 kilometers) an hour. It draws power from two lithium-ion rechargeable batteries, which provide more than four hours of continuous operation on a single charge. Its advanced manipulator offers four independent degrees of freedom: shoulder, elbow and wrist joints that can pivot, and a gripper that can open and close. The manipulator can lift up to 30 pounds (13.6 kilograms) and turn a full 360 degrees on a rotating turret. The PackBot also comes with a pan-tilt-zoom camera and two arm cameras, which means the machine can provide comprehensive views of any device [source: iRobot].

Bomb technicians control these robots with a separate unit -- essentially a laptop -- equipped with a hand controller. They can take a complete visual tour of a bomb's exterior, but more importantly, they can use robots to peek at the device's innards. Many robots come with X-ray scanners that can see through an outer shell and transmit images back to a display on the control unit. These images can be enlarged and digitally manipulated for further analysis, either by on-site technicians or bomb experts at other locations. If X-ray scans prove insufficient or difficult to obtain, the robot's manipulator can remotely open a device, literally peeling away its skin to reveal the components and hardware inside. They can tell if the bomb has a detonator, a fuse or any other defining characteristic that reveals how it was made and how it can be defeated.

Armed with all of this diagnostic information, bomb technicians are finally ready for the most complex and dangerous part of any disposal operation -- neutralizing the threat. As we'll see next, robots, not humans, do most of this dirty work.

The makings for pipe bombs that once belonged to New Hampshire gunman Carl Drega.

© Ed Quinn/Corbis

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Basic Bomb Components

Once bomb disposal experts have thoroughly evaluated a device, they follow "render safe" procedures to make sure an explosion doesn't harm civilians or soldiers. Ideally, they prefer to dismantle a bomb completely, separating explosives from electronics and other components, so they can analyze how it's made. This information then becomes part of an ever-growing bomb disposal knowledge base, which can help technicians on future encounters. But dismantling a device isn't always the most practical or safest solution. Sometimes, the experts opt for a controlled detonation -- the fighting-fire-with-fire approach.

Before we go further, let's get a working knowledge of bomb anatomy going. Although bombs, especially IEDs, can take many different forms, they possess four main components:

  1. The power supply is usually a battery, which supplies energy to the initiator and, in most cases, to the switch. If no power supply is present, then a mechanical switch triggers the initiator.
  2. The initiator causes the bomb to explode. It can take many forms, depending on the nature of the explosives. One of the most common initiators is a blasting cap, a small tube filled with a volatile substance such as mercury fulminate.
  3. Explosives: The main charge can be a high explosive or a deflagrating explosive. Bomb makers frequently pack ball bearings, screws or nails around the main charge to maximize damage and casualties.
  4. Anything that sets off the initiator can be used as a switch. Bomb makers sometimes use wireless devices, such as cell phones, key fobs or walkie-talkies. Other times, they opt for wired triggers, such as trip wires, trip plates and timers.

Dismantling a bomb requires that these different components be teased apart without causing the main charge to explode. Controlled detonation represents a different strategy. Instead of trying to prevent the device from exploding, bomb disposal teams initiate an explosion on their terms, so they can take control away from an enemy or terrorist group.

Neutralizing the Risk: Controlled Detonation and Disruption

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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.

Lots More Information

Author's Note: How Controlled Detonations Work

Apparently, finding information on the Internet about making bombs is easier than finding information about taking them apart. Those trade secrets -- especially those being developed by the military to defeat IEDs -- are too valuable to post where the whole world can read them.

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Sources

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