How Bombs and Thermobarics Cause Injury and Death

This Story Is adapted from In the Waves: My Quest to Solve the Mystery of a Civil War Submarine, by Rachel Lance.

The war in Ukraine is new. The patterns of injuries in that war are anything but. Since the 1867 invention of the world’s first high explosive, TNT, people have been inflicting these same patterns of blast trauma on each other with regularity. Sometimes it seems like we even do it with eagerness. Every few decades, we concoct a new delivery vehicle to enhance the mayhem, such as cluster bombs or thermobarics, but the underlying physics of an explosion, and the vulnerable anatomies of our softest body parts, has not changed.

At the start of each new war, false claims about blast trauma start to fly as quickly as the shrapnel. A month into this one, we already have leading public figures making inaccurate declarations about how thermobarics “suck” the air out of your lungs. (They don’t, but more on that further down.) Regardless of the level and prevalence of the many misunderstandings about blasts, one thing is inarguably, eternally true: People near explosions might die. Here’s how that really works.

Medically speaking, the injuries from an explosion are neatly categorized into one of four tidy bins, which are labeled by numbers: primary, secondary, tertiary, and quaternary. A blast victim might receive only one type, or they can receive a grab bag of trauma containing any painful mixture of the four. Quaternary trauma is a sort of “other” pile of things that can, but do not always, occur as the result of a blast, such as burns, chemical agents, or radiation exposure. Tertiary trauma is the injury type that most people expect—think an action hero injuring his back after getting blown across the room. Notably, tertiary trauma almost never happens in the real world. Secondary injuries are unfortunately an overwhelmingly common injury type. They are the result of objects, like shrapnel, or even fragments of the bomb casing, getting thrown and hitting a person because of the explosion. Secondary injuries are dark, and visually horrifying, as they frequently take the forms of trauma to the limbs, cuts deep enough to reach the skeleton, and amputations.

These three injury types— secondary, tertiary, and quaternary— make obvious sense as the expected possibilities. Primary blast injuries, on the other hand, are an impressive, sometimes invisible, horrifying fluke of nature. They are the byproduct of the bizarre physics of explosions mixed together with human frailty. Primary injuries result from solely the pressures produced by an explosion, usually because of a shock wave.

To understand how a shock wave maims, first it is crucial to understand how a shock wave is born. Normally, sound moves like billiard balls on a massive, smooth felt table. First, a noisy event occurs, like an impact. A gas molecule in close proximity to the action gets pushed away: This is the cue hitting the cue ball. The cue ball travels outward until it hits the 4-ball, another gas molecule. Clunk. They impact, and the cue ball transfers some of its energy to the 4. Both balls now move, slightly slower and in an outward direction, until they impact other balls, hitting their next closest neighbors. The overall wave front of the motion moves forward, but each individual ball travels only slightly across the table. The motion gets passed outward, expanding and slowing just a bit with each collision as the leading edge of movement travels across the table.

www.wired.com

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