Carbon Dioxide as a Measure of Indoor Air Quality-October 2018

Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety

October 2018

IN THIS ISSUE: Carbon Dioxide as a Measure of Indoor Air Quality

Diagnosing indoor air quality (IAQ) complaints can be both a simple and complex process. According to the National Institute of Occupational Safety and Health, most IAQ issues are related to the HVAC system. One of the tools to diagnose HVAC problems that can be used by any safety professional is to measure Carbon Dioxide.  This gas is a normal component in the atmosphere and is exhaled as part of human and animal respiration. Indoor CO2 can be a good indicator of how well the HVAC system is working in a building and can help identify specific problems.

  • 250-350 ppm is normal background level for indoor and outdoor air.
  • 350-100 ppm indicates good air exchange
  • 1000-2000 ppm is associated with complaints about drowsiness, headaches, and stale air.

Measurements should be conducted during the day and can be taken and recorded using detector tubes or direct reading meters. The first readings should be measured outside to establish an environmental baseline. If CO2 levels are high, look for a source outside of the building. The second set of readings should be taken while the building is empty to establish an indoor baseline. If these levels are high, look for a source other than the employees who work in the building. Further readings should be taken periodically through the day when it is occupied. It is normal for CO2 levels to rise while the building is occupied and decrease when people leave. If employees leave the building for lunch, levels may decrease and increase as they return.

If the HVAC system is working properly, CO2 levels should stay below 1000 ppm. Levels of CO2 above 1000 ppm can be caused by insufficient makeup air from the outside (20 percent is recommended.), a malfunctioning HVAC system, poor maintenance, insufficient design, or changes in the use or number of occupants inthe building for which the HVAC was not designed. High levels of CO2 in specific locations may indicate dead spots or stagnant air flow, blocked air ducts and registers, or equipment or nearby process that generate carbon dioxide.

Indoor air quality issues can be a complex matter that may involve considerable time and expense to resolve issues. The use of carbon dioxide measurements can be a useful tool to determine if the HVAC system is part of the problem and if further testing and evaluation is needed.

For more information on this topic and to discuss your company’s safety and industrial hygiene needs call OccuSafe at (214) 662-6005 or visit us at

OccuSafe Industrial Hygiene & Safety, Inc. provides skills and expertise to recognize, evaluate and control hazards and injuries in the areas of industrial hygiene, occupational safety and health. OccuSafe services companies of all sizes in a range of industries.

This newsletter is published monthly by OccuSafe Industrial Hygiene & Safety Services, Inc. Feel free to forward it to friends and colleagues or see past newsletters at

Comments are closed.