Minneapolis got the nickname Mill City because of how many flour mills it had. They were quite dangerous because the flour particles would ignite from any errant sparks. One mill blew up and was turned into a museum:

https://en.m.wikipedia.org/wiki/Mill_City_Museum

The first Washburn A Mill, built by Cadwallader C. Washburn in 1874, was declared the largest flour mill in the world upon its completion, and contributed to the development of Minneapolis. On May 2, 1878, a spark ignited airborne flour dust within the mill, creating an explosion that demolished the Washburn A and killed 14 workers instantly. The ensuing fire resulted in the deaths of four more people, destroyed five other mills, and reduced Minneapolis's milling capacity by one third. Known as the Great Mill Disaster, the explosion made national news and served as a focal point that led to reforms in the milling industry. In order to prevent the buildup of combustible flour dust, ventilation systems and other precautionary devices were installed in mills throughout the country.