Washburn A Mill explosion in 1878

On May 2, 1878, the Washburn A Mill in Minneapolis, then the world's largest flour mill, exploded, killing 18 people and destroying the structure. The mill was a seven-story stone building built in 1874 and represented Minneapolis's industrial golden age.

Cause of the explosion

The cause of the disaster was determined to be the ignition of accumulated flour dust by a spark generated from two mills turning empty. An investigation by two professors from the University of Minnesota concluded the explosion was not due to sabotage or a classic mechanical failure but rather the explosive properties of the flour dust itself.

Impact on milling industry safety

The incident led to significant changes in the milling industry's safety standards. Engineer William de la Barre was hired to design a new mill equipped with a forced ventilation system to evacuate the dust, which became a foundational element for the safety standards of the milling industry.

Scope of the disaster

The explosion was so powerful that the shockwave was heard 16 kilometers away in St. Paul. Fourteen workers in the mill died immediately, and four more died in the subsequent fires at neighboring mills, bringing the total to 18.

Understanding the danger of flour dust

The investigation revealed that the rapid combustion of flour dust, when suspended in the air as fine particles, could create a devastating pressure wave. This understanding led to the implementation of forced ventilation systems and dust collectors, which are now standard in industrial settings.

Legacy of the 1878 explosion

The principles established after the 1878 explosion continue to influence modern industrial safety practices, as seen in recent incidents like the Quaker Oats plant explosion in Cedar Rapids, Iowa, where an apparent explosion caused a fire but no injuries were reported.