How Explosions Actually Kill

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This story adapted from In the Waves: My Quest for Unraveling the Civil War Submarine MysteryRachel Lance.

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The war in Ukraine is new. The patterns of injuries in that war are not at all like that. Since the invention of the world’s first high explosive, TNT, in 1867, people have regularly inflicted the same explosive injuries on each other. Sometimes it seems that we even do it with diligence. Every few decades, we come up with a new delivery vehicle to amplify the chaos, like cluster bombs or thermobaric, but the basic physics of the explosion and the vulnerable anatomy of the softest parts of our bodies have not changed.

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At the start of each new war, the false claims of blast trauma begin to shatter as quickly as fragments. A month later, we already have leading public figures doing inaccurate statements about how thermobarics “suck” the air out of the lungs. (They don’t, but more on that below.) Regardless of the level and prevalence of many misunderstandings about explosions, one thing is always undeniably true: people near explosions can die. Here’s how it really works.

From a medical point of view, explosion injuries are neatly classified into one of four neat groups labeled with numbers: primary, secondary, tertiary, and quaternary. An explosion victim may only receive one type, or they may receive an injury pack containing any painful mix of the four. Quaternary injury is a kind of “other” phenomena that may, but not always, result from an explosion, such as burns, chemicals, or radiation exposure. Tertiary injury is the type of injury that most people expect—think of an action movie hero injuring his back after being blown across the room by the wind. Remarkably, tertiary trauma almost never happens in the real world. Secondary injuries are, unfortunately, an extremely common type of injury. They are the result of objects such as shrapnel or even fragments of a bomb casing being thrown and hitting a person due to the explosion. Secondary injuries are dark and visually horrifying, as they often take the form of trauma to the limbs, cuts deep enough to reach the skeleton, and amputations.

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These three types of injury—secondary, tertiary, and quaternary—make obvious sense as expected possibilities. Primary blast injuries, on the other hand, are a spectacular, sometimes invisible, terrifying accident of nature. They are the by-product of bizarre explosion physics mixed with human weakness. Primary injuries result solely from the pressure generated by the explosion, usually from the shock wave.

To understand how a shock wave cripples, it is first important to understand how a shock wave is born. Normally, the sound moves like billiard balls on a massive smooth felt table. First, a noise event occurs, similar to an impact. A gas molecule that is in close proximity to the scene of action is repelled: this is a cue ball hitting a cue ball. The cue ball flies outward until it hits ball-4, another gas molecule. Clunk. They hit and the cue ball transfers some of its energy to 4. Both balls now move slightly slower and outward until they collide with other balls, hitting their nearest neighbors. The overall wavefront of motion moves forward, but each individual ball moves only slightly across the table. Movement is transferred outwards, expanding and slowing slightly with each collision as the leading edge of the movement travels across the table.

Sound propagates outward, each molecule of material transferring energy to the next, increasing in range but decreasing in strength as it moves. Eventually it hits the ear and becomes audible, or it hits the wall and echoes back to the source. It moves the same way in water as it does in a gas, except it moves faster because the molecules start to move closer together in the denser liquid.

The shockwave is created when a billiard cue falls into the hands of the most enraged, most irate patron in the room. He is explosive. Apoplectic and red-faced explosives quickly burn out. In fact, the combustion front travels through the entire explosive at a much faster rate than normal sound. Consequently, the entire reaction is too fast for the gaseous products formed by combustion to expand outward normally. The material burns and disappears before the balls can fly out on their own, too fast for them to beat their neighbors at their natural speed. The entire charge reacted, was used up, turned into a tiny superheated ball of pressurized gas before the 4-ball had even received the message. The resulting gases expand simultaneously, together, suddenly, strongly, and the billiard cue pushes, flies, rammed down the length of the table, picking up ball after ball and adding them to the front of the wall of forward-moving molecules, picking them up faster than they can move on their own.

This is how the shock wave develops. Molecules accumulating at the wave front are densely packed by the rapidly expanding gas behind them. They are so densely packed that each molecule can reach its neighbor faster than in a normal situation, and therefore this unique wave travels faster than the speed of ordinary sound.

Molecules downstream get hit without warning. In its purest form, the shock wave instantly goes from zero to maximum pressure; on the chart it is a vertical line followed by a sloping decline back down. If it were a car, it would accelerate from 0 to 60 in exactly zero seconds.

When they reach high enough pressure, these waves can destroy everything in their path. The substantial fabric of objects is set in motion by the momentary increase of the impact, and they disintegrate into chaos, like a porcelain cup thrown on a concrete floor.

Most of the human body tolerates mild to moderate shock surprisingly well. Strong pressure will cause tissue rupture, which is a polite phrase to describe a terrifying concept. However, lower pressure shock waves can pass through most of our anatomy without harm. These waves can move straight through the water without much chaos or destruction, and human bodies are mostly water, after all. The real drama is caused by gas pockets inside certain organs.

In the chest wall, which is mostly water, sound travels at about 1540 meters per second. In the gas pocket, which is mostly air, it moves at about 343 meters per second. Therefore, waves moving through the body that enter any gas pocket are forced to slow down at the interface by about 80 percent. In the lungs, they are forced to slow down to a measly 30 meters per second, which is a 98 percent drop in speed. And since they are forced to slow down, this energy must be transmitted somewhere. It is carried into the thin tissues that form the walls of the lungs. They rupture and tear, and blood squirts into the alveoli, filling the precious gas pockets needed for breathing. This process is called flaking.

Gas pockets in the intestines can cause a similar problem, leading to bruising and tearing of the intestinal tract. The same is true of some of the smaller bones of the skull, especially those that form brittle arches around the sinus cavities. Sometimes these bones show webs of fractures from the primary explosion, but they are difficult enough to damage that these patterns are usually only visible in autopsy reports.

If the shockwave is strong enough to knock a person back, then it is strong enough to kill that person through damage to their lungs. Some blast victims report feeling as if they were thrown back because the rapid changes in blast pressure affect parts of the ears that control balance and orientation. However, as a rule, if the victim was abandoned, then this victim did not survive. That’s why real-world explosions don’t leave a taste for battered action heroes, and why shockwaves inflict few tertiary injuries on the living.

The purpose of thermobaric explosives is to increase the duration of the shock wave. They achieve this goal by mixing other fuels, such as aluminum, which burn more slowly than the main explosive, delaying the reaction and often creating a spectacular fireball as a result. If a normal explosion is like a person who touches an electrified fence and receives one painful but brief discharge, then a thermobaric shock is like as if he tightly grabbed the wires with his hand and did not let go. Violence acts for a longer period of time and causes more damage due to the significantly increased period of time during which it can penetrate the fragile human body. Similarly, the extended shock wave of a thermobaric explosion strikes the human lungs over a longer period of time. The explosion can be felt as a blow to the chest, a sharp, hard blow, after which the victim is suffocated. But there is no evidence that thermobaric pulls air out of the lungs.

Although thermobaric explosives often detonate at lower pressures than conventional high explosives, their shockwaves are such dramatic masterpieces of sustained force that they can generally cause more damage, especially indoors or in densely built cities. . In the 1980s, the Russians developed these bombs to attack caves in Afghanistan. When shock waves bounce off cave walls or other solid structures such as tall buildings, they add to each other. When added, they increase the overall pressure level of the blast wave. Within an enclosed space, the long shock wave of a thermobaric explosion can build up to reach extreme pressure levels of a much larger explosion.

Each air shock wave has a short period of time when the pressure drops to a negative level, creating a small vacuum that sucks some materials back in the direction of the explosion. Since the early 1900s, people have blamed this negative period on injury and injury, and of course, with enough vacuum, it is theoretically possible to damage a person’s fragile lungs. However, the bombing cases of World War II and the brilliant researchers of the bombings of the same period determined that the damage was not caused by this negative phase. Explosions occurring underwater do not always have a negative or suction phase, but even they always kill more easily than comparable explosions in the air.

The idea that air is sucked out of the lungs by thermobaric means is one of the most persistent myths about blast injury, because the terrible, dizzying sensation of being hit by a blast seems to reinforce the idea that some kind of massive injury was inflicted on the body. injury. He has. But, unfortunately, the explosion has many ways to kill.

This passage is adapted from In the Waves: My Quest for Unraveling the Civil War Submarine Mystery, Rachel Lance. Copyright © 2020 Rachel Lance. Published by agreement with Dutton, a division of Penguin Publishing Group, a division of Penguin Random House LLC.

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