Gases from muriatic acid and liquid chlorine, chemicals commonly associated with treating pool water, likely caused the noxious fumes, said Chief Steve Ashbrock of Madeira-Indian Hill Fire Department.

"We're not exactly sure how, but there was some off-gassing from muriatic acid or one of the chlorine agents they use to balance or keep the pool clean," Ashbrock said. Tests on the pool water were neutral, confirming that the substance was airborne, he said.

Firefighters conducted atmospheric tests late Wednesday afternoon inside the athletic complex, which was evacuated after the children became sick around 1 p.m. Ashbrock said the pool equipment also will be checked to determine if a mechanical failure was responsible.

"It may end up being that something failed, that a pump failed or a valve failed. We're looking at all of those things," he said.

Ten ambulances from Madeira-Indian Hill Fire Department and surrounding communities helped transport the sick students to Jewish, Bethesda North and Children's hospitals, while classes remained in session at the Given Road campus where 870 students are enrolled in prekindergarten through 12th grade.

School staff members rode with the youngsters in the ambulance to comfort them, said Jeff Clark, assistant head of school.

The illnesses appeared to be minor, Ashbrock said. One boy vomited but the other children were coughing, tearing, sniffling and suffering other respiratory discomfort, he said.

A maintenance worker who became ill declined hospital treatment and stayed at the school to help with the investigation.

E-mail smclaughlin@enquirer.com