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On this date in 1921, one of the worst industrial disasters in history occurred in Oppau, Germany. A fertilizer stockpile in a chemical plant exploded, killing an estimated 500-600 people and injuring thousands; in addition to destroying 80 percent of the buildings in the town around it. The blast, the equivalent of one-to-two kilotons of TNT, left a football field-sized crater that was 60 feet deep.

The factory, owned by the German company BASF, manufactured ammonium sulfate and ammonium nitrate fertilizer and stored 4,500 tons of the products mixed together in a tower silo. The problem started because ammonium nitrate is more hygroscopic—i.e. it absorbs more water from its surroundings—than ammonium sulfate. As a result, the two substances would bind together and form a solid clog in the silo, making it difficult to remove either of them. Workers struggled to break up the mess with pickaxes—a dangerous proposition, since it brought the risk of being buried alive in a cave-in. So instead, as this 
BBC article details, someone decided to drill holes in the fertilizer pile and insert strategically-placed charges of dynamite. It was a method that had been used successfully many times with ammonium sulfate. What plant officials didn’t realize was that the other fertilizer, ammonium nitrate, had different properties. When it is exposed to the force of a detonating charge, it rapidly and violently decomposes into oxygen and other gases. (That’s the reason that domestic terrorist Timothy McVeigh, who blew up a federal building in Oklahoma City in 1995, chose to use an ammonium nitrate-based fertilizer bomb.)

At 7:30 that morning, plant officials got their chemistry lesson the hard way. As this New York Times account details, a pair of explosions lifted the factory off its foundations into the air, and caused it to collapse into a heap of rubble and chemical fumes. The shock was felt for 50 miles around. Three railroad trains full of workers arriving for the morning shift were blown into the air. One witness described a hail of bricks, beams, and mortar that rained down like a deadly hail from the sky. 

You would assume that as a result of the Oppau disaster, people would learn to be careful handling ammonium nitrate. Alas, the lengthy list of other ammonium nitrate-related catastrophe—including the 1947 fire and explosion of a ship loaded with the fertilizer in Texas City, Texas, which killed 580 people—suggest otherwise. Worse yet, terrorists eventually figured out that ammonium nitrate packed into a truck could be turned into a nasty weapon, as Timothy McVeigh demonstrated by destroying a federal building in Oklahoma City in 1995, killing 168 people

And with that, here are the science and technology stories of the day.

Space Shuttle Discovery rolls out to launch pad for the last time today. The workhorse spacecraft has spent the equivalent of a year in orbit.

Earth’s highest coastal mountain is moving. 
Columbia’s Sierra Nevada de Santa Marta is rotating, which will create a new geological basin.

Arctic bacteria hibernate for as long as 100 million years. Now, that’s a nap for you.

Proposed law would empower federal agents to shut down music and movie piracy web sites worldwide. Some in Congress think national sovereignty has 
become obsolete in the Internet age, apparently. We’ll see what other countries think of that.

Lasers can make molecules super-cool. This breakthrough may hasten the development of nano-scale computers.

Giant spiders cast web over river, using super-material. 
It’s the strongest silk ever discovered.