Carbon monoxide sickens 42 kids at Ga. school

"We were really lucky that this didn't go any further than that," Khan said.

Davis, the superintendent, said the investigation continues into what caused the leak. He said authorities suspect the issue started with the boiler, which passed state inspection in 2011 and was not due for another look until 2013.

Other students were sent to a nearby middle school until their parents picked them up.

Fire officials ventilated the building and school district officials Monday night said classes would resume Tuesday at Kennedy Middle School, about four miles away. Stephen Alford, a school district spokesman, said the investigation is ongoing and the building has not yet been cleared for occupancy. Officials Monday were unsure of how long it may take for the investigation to be completed.

In Baltimore last year, officials vowed to put carbon monoxide detectors in all of the system's approximately 200 schools after two carbon monoxide leaks within a week's time at one of the schools.

City officials in Baltimore said the battery-powered detectors cost $15 each wholesale.

Hon, with the Georgia Poison Center, said children can be more susceptible to carbon monoxide than adults due to their size.

She said it can be easy for initial symptoms of carbon monoxide poisoning to be confused with the flu since both include malaise, headache, nausea and vomiting. A few key differences: Carbon monoxide poisoning generally does not cause a fever, and a person usually starts feeling better once he or she is moved to an area with fresh air, Hon said.

Most children did not show severe symptoms, likely because their exposure was brief and because the leak originated far from them, Hon said.

"The good news is that they sound like mild to moderate symptoms," Hon said. "Luckily those kinds of exposures do not carry significant long-term health risks, especially with the children involved."

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Associated Press writers Christina Almeida and Phillip Lucas contributed to this report.