CHICAGO (AP) _ A faulty heating system blew carbon monoxide fumes through an elementary school, causing students to vomit and pass out in classrooms and halls, authorities said.

''Kids were just laying on the floor, unconscious,'' said janitor Raymond Muirhead, 30. ''I just felt a little dizzy, but I was more concerned about getting the kids out.''

Thirty-eight students and four teachers from Delano Elementary School on the city's West Side were overcome by the fumes and taken to six area hospitals where most were treated and released, officials said.

Authorities evacuated 900 students and teachers just before noon Thursday when the school's heating system malfunctioned, sending the deadly, odorless gas wafting into classrooms and halls.

Angela Winston, 8, said students smelled something ''like burned marshmallows'' and her head ached.

''When we got out in the hall, everybody started getting sick,'' she said.

Ed Joyce, a spokesman for Peoples Gas, Light & Coke Co., said workers found the carbon monoxide emissions were caused by a clogged exhaust flue in the heating system.