The National Institute for Occupational Safety and Health in the U.S. recently investigated 100 school buildings at the request of school officials. Investigators were experiencing some problems with indoor air quality.

In an incident in Alberta, a few years ago, parents became concerned when school children came down with respiratory symptoms, fatigue, headache and other symptoms. An investigation found that during routine maintenance a few months earlier, a vent that should have been reopened had been left shut.

"There was a whole section of the school that was not being ventilated," says Dr. Patrick Hessel, an epidemiologist at the University of Alberta and the Alberta Asthma Centre. The children certainly did suffer as a result."