We saw thousands of tons of ammonium nitrate explode in 2020 in Beirut, blowing through the city with a force rivaling a small nuke. A similar disaster happened a hundred years ago, with a bigger pile of fertilizer, but someone hit the ‘blow this place to kingdom come’ button on purpose.
They thought it would be fine, like it had been twenty thousand times before.
Today’s Moment of Science… the 1921 Oppau Explosion.
A BASF plant was built in Oppau, Germany in 1911 to produce ammonium rich fertilizers. They switched from ammonium sulfate to ammonium nitrate during WWI because they were having trouble getting sulfur from international suppliers. Something about a shortage. Or maybe countries wanted to avoid sending a key ingredient for chemical weapons to one of the countries spritzing mustard gas across Europe.
After the war, they produced an ammonium sulfate and ammonium nitrate mixture called ‘mischsaltz,’ or ammonium sulfate nitrate. Ammonium nitrate is hygroscopic, a quality of attracting water out of the air. Under the force of its own weight, mischsaltz could compact and harden into a cake of potentially explosive fuckery. Though workers could get at it with pickaxes, that risked the ammonium sulfate nitrate possibly shifting beneath their feet, burying them under their work.
So they chose the much safer option: blowing shit up.
Surprisingly, this was common practice at the time. It had been observed that, below sixty percent ammonium nitrate, there was no risk of detonation. Their mixture was about 50/50 of the two substances. It was totes fine.
There were other things happening in that silo that they would eventually figure out were conducive to conflagration. A new process they used to dry the ammonium salt mixture had increased its explosivity. It was also understood that some areas of the silo had accumulated higher amounts of ammonium nitrate than others, forming a readily accessible, highly explosive dust. Leave a silo full of chemicals out to bake for a while with a quality management system involving pickaxes and dynamite, you’ll miscalculate something eventually.
On September 21, 1921, they had to gnaw off a chunk of mischsaltz. So on with the dynamite they went, as they’d done a reported 20,000 times before.
Witnesses heard two explosions, and a piece of this world was torn from existence.
Where there once was a silo, there now stood a crater twenty meters deep and over a hundred meters across.
With only about 10% of the total load detonating, it blew with the force of about 1,000 tons of TNT, not dissimilar in impact from a little nuke. The pressure wave from the explosion shattered windows, collapsed homes, even tore roofs straight off buildings as far as 25km away, with damage observed much further out than that. The explosion was said to be felt hundreds of miles away in Munich.
Estimates tend to place the death toll at 560 people, and approximately 2,000 more were injured. Most structures in the small town were destroyed, leaving 6,500 homeless. With everything and everyone involved in the accident obliterated, no firm answers on what went wrong were ever found.
They still store ammonium nitrate and ammonium sulfate together, but new technology prevents the substances from compacting. BASF’s statement on their website basically said “uuuh we stopped producing that stuff for a little while. So it’s cool, right?”
Nobody ever admitted fault.
This has been your daily Moment of Science, reminding you that there’s always another Oppau waiting.
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The Germans were the first to attempt to make ammonia with the Haber-Bosch process. The rest of the world thought the process too dangerous to use. When this factory exploded the world chemical industry immediately rose as one to say “see, we told you so.”
In the September 28, 1921, issue of “Drug and Chemical Markets” was an article claiming the “ammonia converters” at the Oppau Works were to blame for the catastrophe. We find this paragraph:
“The complete demolition of the plant has made it impossible to ascertain definitely the cause of the explosion but it was apparently due to the bursting of one or more Haber ammonia converters, the explosion of a gasometer used for the storage of hydrogen, the bursting of one of the giant compressors used in the process, or experimental work in progress at the time.”
Even the German press was going after Badische Anilin und Sodafabrik for running such a dangerous process. The guys at BASF were screaming that the cause of the explosion was their dynamiting a pile of fertilizer but the Frankfurt Gazette wasn’t having it. Imagine John Cleese telling the plant it isn’t fooling anyone about being dead, and you’re on the right track.
Then an aerial photo of the plant was published. We see a rather impressive crater that used to be a 450-ton mound of fertilizer…and the ammonia production area without a scratch on it.