Here’s what you’ll learn when you read this story:

• The French cargo ship SS Grandcamp was loaded with over 2,000 tons of ammonium nitrate fertilizer in Texas City, TX.
• When the ammonium nitrate detonated, the sky filled with thick clouds of smoke, and shrapnel from the disaster flew wildly throughout the city.
• With 481 fatalities and thousands more injured, the disaster was the worst industrial explosion the U.S. has ever experienced.

April 16, 1947. Faint curls of smoke that thickened into columns rose from the cargo hold of the French freighter SS Grandcamp shortly before its scheduled departure on a transatlantic journey to the harbor of Brest. Then, an unearthly boom reverberated throughout Texas City. Plumes of copper and gold unfurled in the midmorning sky, followed by noxious clouds of ammonium nitrate. Flames tore through the city and engulfed everything in sight, including human beings.

Just across the bay from Galveston, Texas City was founded in 1891, and built its wealth on shipping petroleum and other cargo during the early 1900s. Refineries and factories soon crowded the coast, and after the Second World War, the city became known as an industrial hub, swelling with workers seeking jobs in the postwar economy. Earlier that fateful morning, the crew of the Grandcamp had been loading 2,300 tons of ammonium nitrate fertilizer onto the ship while it was docked near Shoal Point, a few hundred yards across a channel from the main Texas City docks. What most residents didn’t know was that ammonium nitrate is chemically identical to the explosive compound used in Allied munitions throughout World War II, and that the cargo aboard the Grandcamp was, in fact, surplus military stock repackaged for agricultural use.

Understanding the Texas City disaster means understanding ammonium nitrate. The substance is highly explosive, and while it won’t spontaneously combust, it can easily be triggered to explode if it’s heated rapidly or if something else is detonated nearby. It’s also at a higher risk of breaking out in flames if it’s overheated while confined, as it was on the ship. En route from Houston to Brest, the Grandcamp paused at Texas City because Houston had recently banned the substance from its own port, knowing how temperamental it was.

On the Grandcamp—which had arrived carrying cotton, twine, tobacco, machinery, and even shelled peanuts—sacks of fertilizer were packed into the confines of the ship’s hold. Someone, at some point, also carelessly tossed in the butt of a cigarette that had not been completely extinguished. Another worker picked up the unmistakable smell of smoke around 8:00 am. When smoke was seen rising from the fertilizer sacks, attempts were made to put it out with water and two fire extinguishers, but the captain was more concerned about water potentially damaging other cargo. He instead decided to shut the hatches of the hold and poured in steam.

It didn’t work.

Smoke rising from the fire was visible for miles, and by the time the local volunteer fire department and firefighters from the Republic Oil Refining Company rushed to the scene, it was too late. Frantically blasting the ship with hoses did nothing, as intense heat vaporized the water on impact. Eventually, at 9:12 am, the Grandcamp exploded. Unfortunate crewmen and firefighters were incinerated. Shrapnel flew through the air as far as a mile out, killing or injuring onlookers and people headed to work at the nearby Monsanto plant, where 145 workers would lose their lives while on shift. Tanks at surrounding oil refineries were gouged open by chunks of metal from the ship’s hull. The orange billows of smoke that had flared in the sky went black, and a massive tidal wave towered over Texas City. Some survivors thought the apocalypse was nigh.

“I thought ‘My God, it was a nitrate fire,’ said survivor William Lane, a retired Monsanto chemist, in a documentary. “Everyone’s reaction was the same, whether you were standing or sitting, you were instantly on the floor or on the ground from the tremendous earth shock that came from the detonation, and no one in their wildest imagination can imagine how terrible all this was.”

Lane had long suspected that the ammonium nitrate posed a serious hazard, and now his fears were materializing in real time. The roof of the Monsanto building collapsed onto the employees below, who stumbled out screaming. By the time the fire burned itself out, the entire complex would be demolished. With no hospital in Texas City, makeshift first aid stations sprang up almost immediately, soon supplemented by an influx of outside responders, and when the morgue reached capacity, the local high school gymnasium was pressed into service as a holding place for unidentified bodies.

As the inferno spread through the city and and consumed whatever was in its way, another boom rang out from the harbor—the SS High Flyer, another ship carrying ammonium nitrate fertilizer and berthed dangerously close to the Grandcamp, had detonated. The harbor blazed in this new round of devastation as, not even 24 hours after the initial explosion, a mushroom cloud of smoke and fumes was blasted 300 feet into the air, claiming even more lives. Headlines following the blast were sensational. Extra! Residents evacuating blast-stricken town!

It was the worst industrial accident the U.S. had ever seen—a record it still holds to this day—and it would take Texas City decades to recover. But recover it did. Residents resumed their jobs when rebuilding was completed, and many others refused to leave what had been their lifetime home. Today, a phoenix fountain outside the Charles T. Doyle Convention Center honors the fallen and the city’s rebirth from its ashes.