What is considered an elevated CO2 concentration?

Generally, a CO2 concentration above 1,100 ppm for more than 30 minutes would be considered an elevated concentration; however, it only means that outdoor air ventilation is being provided at a rate that is less than 15 cfm/person as recommended by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). In an occupational setting, the Occupational Safety and Health Administration’s (OSHA) Permissible Exposure Limit (PEL) for CO2 is 5,000 ppm. This 5,000 ppm threshold is far above the 2,000 ppm CO2 concentration that is considered to be an indicator of poor indoor air quality and well above the levels found in HCPSS cafeterias that rarely exceed the 1,100 ppm target.