What causes an elevated CO2 concentration in schools?

The rate at which CO2 is generated within an indoor space is proportional to the number of occupants in the space. If outdoor air ventilation is not provided at a rate of 15 cfm/person, an elevated CO2 concentration above 1,100 ppm can result.

It is important to note that carbon dioxide (CO2) is a gas that is generated by humans when they exhale. It is not to be confused with carbon monoxide (CO).