How Dynamite [literally] Shaped The World

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How Dynamite [literally] Shaped The World
The explosive has made almost every aspect of modern technology possible—and caused its share of disasters along the way.
MAY 26, 2020


Excerpts:

To understand why dynamite was so revolutionary, says Larry Glenn Hill, a detonation physicist with Los Alamos National Laboratory’s High Explosive Science and Technology group, you have to understand the instability of its precursor.

“Detonation is a wondrous and highly specialized process, which involves the cooperation of two structures,” Hill explains. “The first is a shock wave, and the second is a burn wave.” A shock wave is a sharp rise in pressure, temperature, and density that travels at supersonic speeds. Picture it as the motion that occurs when you release a tightly coiled spring. As all that energy is expended, it produces heat, which is responsible for the fiery part of an explosion. “A detonation can be viewed as a burn-supported shock wave, or a shock-triggered burn wave; however one chooses to look at it. It is either and both.”

Under the right conditions, like being bumped around in a shipping crate or a rail car, nitroglycerin can develop stress waves that put the liquid into a state of tension. “This can cause the liquid to cavitate. That is, the boiling point is suddenly lowered to the point that a cloud of bubbles quickly forms,” Hill says. “But the next thing that happens is that a compressive wave, reflected from some boundary, comes along and collapses those bubbles.” The collapse produces extremely high temperatures, in the form of an instant shock wave, followed quickly by the burn. In other words, every time Nobel’s Blasting Oil moved, there was a risk it would spontaneously detonate. “It truly is Russian roulette,” Hill adds. “I'm not afraid of much, but liquid explosives make me nervous.”

Working in a laboratory on a barge on Lake Mälaren in Sweden, Nobel set out to stabilize the nitroglycerin by mixing it with something that would make it safe to move and handle. He tried brick dust, waste wood, and coal dust, letting the materials absorb nitroglycerin and then attempting to set them off with his blasting cap, before finally landing on diatomaceous earth, a dirt-like substance made of fossilized algae, in 1867. It works by turning the liquid nitroglycerin to a dough-like consistency, preventing bubbles from forming.

“Of course, this mechanism was not known in Nobel’s day,” Hill says. “He was just desperately trying things to save his reputation and his empire, and found that adding diatomaceous earth did the trick.”

Nobel had made dynamite tame enough for the miner’s toolkit, but it wasn’t a perfect—or perfectly safe—solution.

“The dynamite would sweat, and if left it in one place for a long time, the nitroglycerin would tend to pool on the bottom,” Hill says. “In cold weather, the nitroglycerin would freeze, which desensitized it. Miners learned to carry the starting pieces (the pieces detonated with a blasting cap, which would initiate others in the chain) around in their socks to warm them up.”

Though much less volatile than pure nitroglycerin, dynamite would never be completely safe. In September of 1904, a trolley car in Boston hit a 50 lb box of dynamite which had fallen onto the tracks from a cart. The explosion killed 10 people in a blast radius more than 100 feet wide. In 1913, a sudden explosion of 340 tons of dynamite being transferred from a barge to a British steamship in Baltimore Harbor killed at least 50 people and wounded many more. In 1926, one of the biggest steam shovels in the world was destroyed, and its two operators killed, when it hit an old pocket of dynamite that failed to explode, was forgotten, or both – called a “coyote hole” – at a copper mine in Jerome, Arizona.
 
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