Seventy-three years ago, on an April morning at the port of Texas City near Galveston, crew members of the SS Grandcamp were busy loading thousands of pounds of ammonium nitrate.

“It was the beginning of a beautiful, cool day,” the Houston Chronicle reported, “a breeze was coming out of the north.”

Around 8 a.m., someone noticed smoke coming from the cargo area.

And then, boom.

A massive explosion sent a mushroom cloud more than 2,000 feet toward the clear blue sky, triggering not just a massive fire at a nearby chemical plant but frightening images similar to those that resulted from the United States dropping two atomic bombs on Japan in 1945.

“The Russians have dropped a damn A-bomb on us,” a nearby worker told his buddy, according to the Chronicle.

It was not the Russians.

It was ammonium nitrate, a highly explosive material commonly used to make fertilizer.

When ammonium nitrate blows up, it blows up big, just as it apparently did earlier this week at a port in Beirut, where the resulting mushroom cloud drew comparisons to the bombing of Hiroshima. But to Texans, the images from the Beirut explosions were an eerie reminder of the disaster suffered there decades ago.

More than 500 people died, with thousands more injured. It was one of the largest explosions in U.S. history.

Earlier this week, KTRK-TV aired footage from the explosion and recounted the aftermath:

The explosion caused a 15-foot wave that crashed onto the docks and flooded surrounding areas. Windows shattered as far away as Houston, and vibrations from the blast registered on a seismograph in Denver, Colorado. A barge anchored in port was blown out of the water and landed 110 feet away.
Everyone standing nearby, including almost the entire Texas City Volunteer Fire Department, was killed instantly. Buildings near the blast were flattened and the neighboring Monsanto plant was destroyed.
Flaming debris triggered fires at nearby chemical plants and refineries.
The call for help was put out across the country and rescue workers from all over responded to the disaster.

The Texas City disaster was not a one-off. In between it and the devastation in Beirut, there have been several other ammonium nitrate disasters, according to the Associated Press.

In 2015, 173 people were killed in the port city of Tianjin, China, when a warehouse containing ammonium nitrate exploded. Two years before that, there was a massive explosion at a fertilizer company in West, Tex.

The substance has also been used in criminal and terrorist attacks, including Timothy McVeigh’s 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City.

Tommy Muska, the mayor of West, Tex., was reminded of the explosions in his state after the Beirut incident.

“We don’t seem to learn that chemical is deadly,” Muska told the Associated Press. “I feel for those people in Beirut, I surely do. It brought back a lot of memories.”

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