From the Associated Press — About 20 students and staff members at a western Michigan school have been treated for breathing problems caused by an unknown irritant. The Muskegon Chronicle and WOOD-TV report hazardous materials teams were inside Muskegon Catholic Central on Tuesday trying to determine the cause of the irritant. Classes have been cancelled for the day. Authorities say there is no evidence of foul play, and those treated at and released from hospitals weren’t considered to be critical. Reported symptoms included shortness of breath, coughing and chest tightness. Michigan Catholic Central President Ken Rasp said he could feel something in his throat that made him want to sneeze. About 450 people were in the school at the time of the evacuation. Air samples were expected to be sent to a laboratory for testing.