The Great Mill Disaster: When Flour Exploded

The evening of May 2, 1878, was ordinary at the Washburn A Mill. Fourteen workers manned the seven-story building, tending the machinery that made Minneapolis the flour capital of America. The Mississippi roared through the millrace below. Flour dust hung in the air, fine as talcum powder, coating every surface. Nobody thought twice about it.

At 7:10 PM, something sparked. In less than a second, the flour dust suspended in the air ignited — not a fire, but an explosion. The blast leveled the Washburn A Mill instantly, killing all fourteen workers inside. The shock wave jumped to neighboring buildings. Five more mills exploded in quick succession. When the chain reaction finally stopped, eighteen people were dead, half of Minneapolis's flour-milling capacity was destroyed, and a city was in ruins.

The Great Mill Disaster, as it came to be known, was the worst industrial accident Minneapolis had ever seen. It was also a turning point — the moment when flour milling stopped being a craft and started being a science, when industrial safety became something more than an afterthought. Minneapolis would rebuild bigger and safer than before. But first, it had to bury its dead.

The Mill City

The Mill City was built around its mills. At St. Anthony Falls, the Mississippi provided unlimited power. Wheat from the northern prairies flowed in by railroad. And the Washburn A Mill was the largest of them all — a seven-story giant, technologically advanced, capable of producing 1,500 barrels of flour per day.

What nobody fully understood was the danger. Flour dust, suspended in air at the right concentration, is explosive. The mills were full of it — clouds of fine powder that coated machinery, hung in shafts of light, settled on workers' clothes. A single spark could turn a flour mill into a bomb.

The Explosion

The most likely cause was a millstone. Two stones grinding together could produce sparks if they ran dry or came into contact. On the evening of May 2, something sparked — maybe the millstones, maybe static electricity, maybe a lantern. The exact cause was never determined.

What happened next was instantaneous. The spark ignited the flour dust suspended in the air, creating a fireball that expanded faster than sound. The pressure wave was catastrophic. The seven-story Washburn A Mill was demolished in less than a second. Debris was thrown hundreds of feet into the air.

The Legacy

The Washburn A Mill operated until 1965, when the milling industry finally left Minneapolis. The building sat abandoned for decades, caught fire in 1991, and was partially destroyed. What remained — massive stone walls, empty windows, industrial ruins — became a different kind of landmark.

In 2003, the Mill City Museum opened in the ruins of the Washburn A Mill. The museum tells the story of Minneapolis's flour milling industry — including the 1878 explosion. Visitors can see the mill's surviving structure, learn about the workers who died, and understand how flour made Minneapolis what it is today.

At Lakewood Cemetery, the monument to the eighteen dead workers still stands. A sheaf of wheat. A millstone. A broken gear. The names of men who died when flour became fire, in the explosion that changed an industry and built a city.

Minneapolis was built on flour. The mills at St. Anthony Falls made the city — drew workers, generated wealth, put Minneapolis on the map. But flour kills too. On May 2, 1878, eighteen men learned that lesson, and Minneapolis learned it with them.

The city rebuilt. The industry reformed. The knowledge gained from those eighteen deaths made mills safer worldwide. It's a brutal equation — progress paid for in lives — but it's the equation Minneapolis was built on. The Mill City remembers, even if the mills are gone.