Carbon Dioxide Concentration - Comfort Levels
Indoor comfort and air quality includes parameters like
- temperature
- odor
- high or low levels of gases
Since CO2 is exhaled by people at predictable levels the content of Carbon Dioxide in the indoor air can be used as a significant indication of air quality.
Fresh supply air correlates to the indoor level of CO2 as:
- 15 cfm ventilation rate per occupant - aprox. 1000 ppm CO2
- 20 cfm ventilation rate per occupant - aprox. 800 ppm CO2
Normal CO2 Levels
The effects of CO2 on adults at good health can be summarized to:
- normal outdoor level: 350 - 450 ppm
- acceptable levels: < 600 ppm
- complaints of stuffiness and odors: 600 - 1000 ppm
- ASHRAE and OSHA standards: 1000 ppm
- general drowsiness: 1000 - 2500 ppm
- adverse health effects may be expected: 2500 - 5000 ppm
- maximum allowed concentration within a 8 hour working period: 5000 - 10000 ppm
- maximum allowed concentration within a 15 minute working period: 30000 ppm
The levels above are quite normal and maximum levels may occasionally happen from time to time. In general - ventilation rates should keep carbon dioxide concentrations below 1000 ppm to create indoor air quality conditions acceptable to most individuals.
Extreme and Dangerous CO2 Levels
- slightly intoxicating, breathing and pulse rate increase, nausea: 30000 - 40000 ppm
- above plus headaches and sight impairment: 50000 ppm
- unconscious, further exposure death: 100000 ppm
Carbon Dioxide Standard Levels
The recommendations in ASHRAE standard 62-1989 are
- classrooms and conference rooms 15 cfm per occupant (person)
- office space and restaurants 20 cfm per occupant
- hospitals 25 cfm per occupant
- 1 cfm (ft3/min) = 1.7 m3/h = 0.47 l/s
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