What makes a bomb so deadly
"Please leave your apartment!"
Almost every day somewhere in North Rhine-Westphalia (NRW) an area has to be evacuated because a bomb has been found. That means: Nobody is allowed to stay in the restricted area. Depending on the size of the bomb, this restricted area can have a radius of 50 meters to one kilometer.
In a city like Cologne, several thousand people are quickly affected. While they are leaving the danger zone, the ordnance disposal personnel make their way to the bomb.
The duds are mostly discovered during construction work, several hundred every year. In 2018 it was almost 3,000. Several decades after the end of the Second World War, it is surprising at first that so many duds are still stuck in the earth.
But it becomes understandable when you realize the unbelievable mass of bombs that were dropped on NRW: 700,000 tons. And a large part did not explode directly and was not cleared away later, but fell into oblivion and remains dormant in the earth as an explosive danger to this day.
Feel the detonator with a sure instinct
Put simply, a typical aerial bomb consists of two parts: a small detonator, about the size of a bubble bottle, and the bomb body filled with the explosive TNT. Separately, the two parts are relatively harmless. They only become a deadly danger in the connection, i.e. when the detonator ignites the explosive. The aim of the mitigation is therefore to separate the two parts from each other.
In order for the detonator not to be triggered, the ordnance disposal specialist must first know what type of detonator it is. And since the bomb is usually somewhere in the dirt, difficult to access and half rusted, it usually feels the detonator. So a sure instinct is required.
A distinction is made between two types of detonators: impact detonators and long-term detonators. Impact detonators have a movable firing pin that is held in place by a spring. When the bomb hits, the firing pin rushes forward and hits a fuse, much like a toy gun. This detonator plate triggers a series of booster charges that ultimately detonate the bomb's TNT.
Often, however, the bombs did not fall straight down, but slightly to the side. If they hit the earth at an angle, the firing pin did not receive the impulse in the direction of the ignition plate and did not trigger a chain reaction. The bomb turned into a dud.
If this dud is moved today and maybe even if on its tip, a drop of a few centimeters is enough and the firing pin takes its fatal path.
Long detonator bombs often explode spontaneously
Long-term detonators are even more dangerous. With them, the firing pin is tensioned by a spring and is only held in place by a locking ring made of celluloid plastic. In front of it is a small glass container filled with the corrosive liquid acetone.
When the bomb is dropped, this glass container is destroyed and the acetone begins to dissolve the locking ring. Depending on the thickness of the ring, it can then take hours or days for the firing pin to be etched free, zoom to the ignition plate and trigger the bomb.
However, if the bomb hits at an angle or comes to rest with the tip up, only part of the Acteon will reach the locking ring. It can then take several decades for this to give way. And that happens very spontaneously, without any shock or external intervention. Such a self-detonation occurs around once a year in Germany.
Since the condition of the locking ring cannot be seen from the outside, bombs with long-term detonators are particularly dangerous for the ordnance disposal team. Even a small movement of the bomb can cause an almost dissolved circlip to lose its last hold and lead to an explosion.
Each defuse is different
As soon as it is clear which detonator it is, the ordnance disposal officer can start thinking about defusing it. If it is a simple percussion detonator without additional fuses, it can often simply unscrew the detonator with a pipe wrench.
But there are also impact fuses that are prepared with additional mechanics in such a way that the firing pin also triggers when the fuse is unscrewed. Then, for example, the turning impulse device is used, which the ordnance disposal team also call the "missile clamp". The flat rectangular frame is clamped to the igniter with screws.
A tube with a propellant charge is attached to each of the two opposite sides, similar to a New Year's Eve rocket - hence the name rocket clamp. The ordance disposer ignites them from a safe distance. The rocket clamp then rotates the detonator out of the bomb so quickly that the firing pin strikes nowhere.
In the case of long-term detonators, the munitions disposers like to rely on the water jet cutter. Water is pushed through a small nozzle at high pressure. This makes the jet so hard that it can even cut steel. The device is placed in the front of the detonator and controlled remotely. The vibrations are relatively small, so that the locking ring is hardly loaded and the detonator does not trigger.
Sometimes only new explosives can help against old ones. The bomb is detonated in a controlled manner using modern plastic explosives. That is also what the ordnance disposal team call defusing.
In order to dampen the force of the explosion, the bomb is then enclosed with straw, sand or water and thereby insulated. The aim is to minimize the damage. But as good as “controlled demolition” sounds: The only thing that the ordnance disposal team really control is the time.
Not a job for daredevils
“I am very aware that this can be my last bomb every time. And regardless of whether I defuse a 50-kilo bomb or a 1,000-kilo bomb: If it goes wrong, the result is always the same for me, ”says Karl-Heinz Clemens. He is an experienced ordnance disposal specialist and a calm, level-headed person - but you can still see his concentration during a defuse.
And it is noticeable that he is not wearing a special protective suit. The reason is as simple as it is terrifying: if a bomb goes off while he's working on it, nothing can protect him. The explosive power is just too great.
What bothers Clemens and his colleagues most are people who refuse to leave the restricted area. They mess up the schedule and create additional danger. This is because defusing may only begin when everyone who is not involved has really left the restricted area.
But if people do not leave their homes and have to be laboriously collected by the police, then the ordnance disposal officer has to wait idly. The start of the disarming is then quickly postponed by several hours and suddenly lies in the middle of the night. The ordance disposer then not only has to fight with the dud, but also with darkness and fatigue.
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