Thousands of anti-war protesters gathered in cities around the US on May 10 1972 to demonstrate against the use of mines in Vietnam harbors (Associated Press 1972b). In Minneapolis, crowds totalling a thousand protestered gathered on and near the University of Minnesota campus and police responded with chemical weapons deployed via grenades, sprays, a helicopter and a thermal fogger (Associated Press 1972a; Star Tribune 1972).

The fogger was used to direct the crowd around campus and spread gas over large areas, such as the area known as Scholars Walk (~0.25 mile from Washington Avenue to the Auditorium) (Star Tribune 1972).