It happened on the number 49 Western Avenue bus near Harrison Tuesday night. The Chicago Fire Department's hazardous materials team was called to check the air in the bus to determine exactly what was sprayed. They determined it was from a fire extinguisher.
Someone reportedly sprayed the bus driver the extinguisher, but no one was seriously hurt. Still, paramedics checked out the driver and passengers as a precaution.
Chicago police say they are looking for suspects.