Why Did the a Mill Explode?

Photo of debris and rubble where the Washburn A Mill stood before the explosion, 1878.

Ruins of Washburn A Mill after explosion, Minneapolis, 1878.

Photographer: Jacoby

Minnesota Historical Society Photograph Collection, Location no. MH5.9 MP3.1W r46; Negative no. 7286-A

The A Mill had used the middlings purifier, which made the flour better but produced a large amount of dust. It was this dust that sparked the explosion that wiped out most of the milling district and killed 18 workers.