CHICAGO (STMW) — About 25 children were hospitalized in good condition after a carbon monoxide leak at a school in the Far South Side Burnside neighborhood Monday afternoon.

The children were suffering from nausea, vomiting and headaches before being hospitalized in good condition, according to Fire Media Affairs. Initially, 14 children were hospitalized.

A Level 1 HazMat was called about 12:45 p.m. for the leak at Harold Washington Elementary School at 9130 S. University Ave., according to Fire Media Affairs.

Firefighters ventilated the third floor of the building with fans and evaluated the students before sending them to hospitals.

The leak may have been due to a faulty boiler.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2012. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)