Washburn A Mill Explosion, 1878

On the evening of May 2, 1878, the Washburn A Mill exploded in a fireball, hurling debris hundreds of feet into the air. In a matter of seconds, a series of thunderous explosions—heard ten miles away in St. Paul—destroyed what had been Minneapolis' largest industrial building, and the largest mill in the world, along with several adjacent flour mills. It was the worst disaster of its type in the city's history, prompting major safety upgrades in future mill developments.

The massive A Mill, only four years old at the time, had been built by Cadwallader Washburn, a businessman from LaCrosse, Wisconsin, in the heart of Minneapolis on the Mississippi River, near St. Anthony Falls. The seven-story flour mill was powered with river water, which was diverted through a canal that ran inside its lower level. With two hundred workers, it was one of the city's largest employers.

At six o'clock that evening, the mill's large day crew completed its shift. Fourteen men who made up the night crew arrived. An hour later, three deafening explosions echoed out, reverberating in waves all over town. All fourteen workers were killed. Within minutes, the fire had spread to the adjacent Diamond and Humboldt mills. They also exploded, killing four more workers.

The city's fire department worked all night to contain the fire. Their efforts were futile. The intense heat prevented firefighters from setting up rigs and hoses close enough to the site to have much impact.

The next day, on May 3, the Minneapolis Tribune told its readers, "Minneapolis has met with a calamity, the suddenness and horror of which it is difficult for the mind to comprehend."

At the inquest into the deaths of the eighteen workers, John A. Christian, the A Mill's manager, explained that rapidly burning flour dust had caused the disaster. His explanation was later confirmed by two University of Minnesota professors, S.F. Peckham and Louis W. Peck, who reviewed a series of controlled experiments that caused flour dust to explode. Peckham and Peck concluded that two of the millstones, running dry, had rubbed against each other, causing a spark that ignited the dust.

As the furor over the explosions began to subside, the Tribune speculated about the impact of the event on the local milling industry, now that one-third to one-half of the city's production capacity had been destroyed. The newspaper noted that Minneapolis had recently surpassed St. Louis and Buffalo in milling production and was now the country's leading flour producer.

Cadwallader Washburn, who had rushed to town from his Wisconsin home after hearing news of the calamity, announced that he would rebuild, even as the embers from his destroyed plant were still glowing.

Washburn kept his word. By 1880, his new A Mill was up and running. It was safer and more technologically advanced than its predecessor, with a greater production capacity. The milling magnate opened his new plant in time to take advantage of the economic boom that Minneapolis would experience during the last two decades of the nineteenth century and into the twentieth. The city's milling production continued to increase, peaking during World War I.

The A Mill continued to operate for several more decades, even as the local milling industry declined. It finally closed in 1965, remaining vacant until a 1991 fire destroyed the building.

In 2003, the Mill City Museum, which incorporates the ruins of the A Mill, opened to the public. The museum interprets Minneapolis's milling history and the role of water power in promoting the city's growth during its early decades. Visitors who ride the museum's Flour Tower elevator—an educational presentation that offers a glimpse into each of the mill's floors—hear a thundering boom intended to evoke the 1878 explosion.

Another reminder of the nineteenth century disaster is located four miles away in Minneapolis' Lakewood Cemetery. There, a monument erected in 1885 honors the memory of the eighteen men who were killed. A plaque lists their names. Just below it, the monument's engravings include a sheaf of wheat, a millstone, and a broken gear.