TCS Daily

Car Bombs vs. Human Beings

By Ralph Kinney Bennett - March 18, 2004 12:00 AM

This is a short, unpleasant article. It's just to remind our readers about the brutal physics of car bombs.

We pointed out in TCS last year (here) the problems these insidious weapons pose in this war. But in a way we all become somewhat inured to "another car bombing," like the one that just occurred at that little hotel in Baghdad.

Indeed, television coverage has a kind of pro forma discretion about these bombings. We see a series of images -- flames against the sky, the flashing lights of the rescue vehicles, the smoking rubble laced with rescue workers searching for victims, walking wounded, blood and dust on their faces, making their way from the scene. We may still watch with a grim fascination but we've seen it all before.

So perhaps it would be useful to take these things down to the level of a single human being so that we can refresh ourselves on just what words like "terror" and "murder" really mean.

This latest car bomb appears to have been a large one. There were estimates within hours that it must have been "a thousand pounds of explosives." And American troops found evidence that at least one 155 mm artillery shell may have been part of the bomb.

But car bombs don't have to be large to be devastating. The type of explosive used (different explosives have different DVs or detonation velocities), the shape of the explosive itself and the type of casing in which it is placed are all factors. The structure of the car used and the position of the bomb in or on the car also help determine lethality. The terrible car bombing in Bali last year reportedly used slightly over 200 pounds of explosives, but it killed 191 people, injured scores and destroyed a lot of property.

Methods of mixing various types of explosives are well known. The web is filled with "cook books" on the subject. The art of shaping the malleable plastic explosive charge to focus the blast wave toward the desired target is another important aspect of what our military now refer to by the sanitized term IEDs -- improvised explosive devices. Shaping usually involves hollowing the end of the charge that is "aimed" at the target building. This inverted cone concentrates the bomb's shockwave.

Most of us have only seen explosions in movies where slow-motion photography or the use of low velocity explosions with lots of smoke and flame create spectacular, lingering visual effects. Real bombs, using a high order of explosives, go off in a millisecond flash doing huge damage in a literal instant. There is little for the eye to linger upon. One moment everything is normal. Then a supersonic boom. Then destruction.

In a car bomb the chief effects on life and property are caused by blast and heat -- from the explosive charge -- and by fragmentation of the bomb casing and the car itself. Sometimes the car is the bomb casing, with the plastic explosive material having been tamped into axle housings, doors or the hollow steel frame of the vehicle.

But let's get back to the people side of this.

The human body's amazing resilience and recuperative powers are well known. We recover from bullet wounds, knife wounds, near-drownings, torture, disease and a thousand traumas brought on by design and by accident.

But a human body seldom comes out alive from the mad perimeter of a bomb's blast. That deadly perimeter is determined by the bomb's size and the power of the explosives inside. For instance, a 2000-pound "general purpose" military bomb (the kind dropped from aircraft) contains approximately 1000 pounds of high explosive. The blast effect perimeter of such a bomb is about 110 feet.

When that car bomb detonated in front of the Mount Lebanon Hotel on Wednesday night any humans close by were subjected to a multiple assault, swift, withering and summary. Those within a few feet of the car were probably torn to small pieces and those pieces were horribly barbecued in a literal flash. Others, perhaps in the hotel itself, were killed by piercing bomb fragments traveling at thousands of feet per second, or thrown at tremendous speed against walls and pillars. Others may have had parts of the hotel structure driven into and through them.

One of the least understood phenomena of a bomb blast is overpressure. Everything in the blast perimeter is subject to a sudden and profound increase in air pressure. This wave of blast overpressure declines rapidly the further it travels. A person 10 feet from a bomb blast will experience nine times the overpressure of a person 20 feet away. But it gets messy and unpredictable. A person who happens to be standing between the bomb and a strong wall is subjected to more blast effect because solid surfaces reflect the blast wave.

You, as you read this, are subjected to normal air pressure of 15 pounds per square inch, depending on how close you are to sea level. The rapidly expanding gases of the bomb push the air out of the way generating air pressures of as much as 700 tons per square inch in the immediate area. But even on the outer perimeters of the blast area overpressures can be deadly.

The human body contains two principal air-filled spaces -- the lungs and the nasal cavity and attached sinuses. A human subjected to a bomb blast wave instantly has hundreds and perhaps thousands psi of pressure pushing on these cavities. A mere 15 psi above normal is considered the threshold for possible lung injury, so imagine what happens to those near the epicenter of a bomb blast.

The chest caves in. The lungs inside it are compressed violently in on themselves -- so violently that the entire network of pulmonary vessels connecting them to the heart and the rest of the body are sheared off.

When the instant of blast overpressure passes, the lungs suddenly re-expand, like a crushed rubber ball rebounding in the hand of a strong man. But now they are filled with a huge volume of blood, blood that should be flowing to the heart and other parts of the body.

Blood that would normally return to the heart through the left ventrical has now overwhelmed the lungs. No blood in the left ventrical equals no blood in the heart equals no pulmonary output to the body. Blood pressure -- zero. The body is instantly starved.

Up above, in the skull, at the same instant, the overpressure works in another way. The nasal and sinus cavities implode. That part of the skull called the cribiform plate ruptures, snaps and may be thrust upward into the base of the brain.

Kind of academic, isn't it? You can die so many ways in the space of a few seconds in a bomb blast.

We in the general public don't hear about these things. Doctors treating those who survived the initial blast use terms we never hear to cover the bloody mayhem being wheeled into them -- pulmonary barotraumas, disseminated intravascular coagulation, lipoxygenation. The patient is probably covered with bruises and scars and blood, but much of the life threatening damage is hidden from view. Even in a big, modern American hospital doctors and nurses would be quickly overwhelmed. Imagine the situation in Iraq.

There will be more car bombs. When you read about them, think for a moment about those victims who are so quickly reduced to mere statistics. These were human beings like you, suddenly subjected to a terrible physical force that is difficult to imagine. Terrorism has been called "the warfare of the weak," and its victims are almost always the weak, the innocent, those simply trying to live their lives -- in the wrong place at the wrong time.

Ralph Kinney Bennett recently wrote for TCS about "Terror's Grand Design."


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