"Pepper spray" was released in a SF BART Station yesterday. Four people were taken to the hospital and "were expected to recover," with the Fire Department's Hazardous Materials dept. finding the material to be pepper spray. The "person" who set off the spray is "still at large."
Pepper spray release hospitalizes passengers at Powell St. station – California Beat
Related note: In 1950, the U.S. military released a "bacterial fog" over San Fransico to test biological warfare programs.