Fumes from chemicals that were inadvertently mixed temporarily forced the evacuation Monday of about 500 people from National Jewish Health, a health system with a national reputation for respiratory care.

Hospital spokesman William Allstetter said most of the evacuees were staff members. About 45 people were transported to other hospitals for treatment, mostly for nausea and respiratory irritation.

The evacuations included about 90 children attending an elementary school for students with respiratory ailments, located on the hospital campus.

Three buildings were evacuated, but the main hospital wasn't affected and doctors were still seeing patients, Allstetter said. Fire officials allowed people back into the buildings about 3 1/2 hours after the spill, though the school remained closed because the children were sent home.

Chlorine and hydrochloric acid were inadvertently mixed during maintenance work at a swimming pool at the elementary school, and the fumes spread through tunnels connecting the buildings, Allstetter said.

Doctors at National Jewish conduct research and provide mostly outpatient care.

In 2007, the hospital gained attention when its doctors diagnosed the first non-factory worker case of "popcorn lung" in a man who ate two bags of microwave popcorn a day. The ailment, formally known as bronchiolitis obliterans, had previously been found only in popcorn factory workers.

That same year, National Jewish treated the first American quarantined by the federal government since 1963. The man was first thought to have so-called extensively drug-resistant tuberculosis, or XDR-TB. Subsequent testing showed he had the less dangerous multidrug-resistant TB.

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