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Engineering ToolBox > Carbon Dioxide Comfort Levels

CO2 acceptance and comfort levels

Even if indoor air quality includes many components, among them

• temperature
• odor
• high or low levels of gases,

testing for Carbon Dioxide - CO₂ - may often be a significant indication of the air quality.

Since CO₂ is exhaled by people at predictable levels and with a measurement of CO₂ the amount of fresh air supplied can be calculated

• a 15 cfm ventilation rate per occupant will correspond to 1000 ppm CO₂
• a 20 cfm ventilation rate per occupant will correspond to 800 ppm CO₂

Normal CO₂ Levels

The effects of increased CO₂ level on adult persons at good health can be summarized as

•  normal outside levels: 350 - 450 ppm
• acceptable levels: < 600 ppm
• complaints of stiffness and odors: 600 - 1000 ppm
• ASHRAE and OSHA standards: 1000 ppm
• general drowsiness: 1000 - 2500 ppm
• adverse health effects expected: 2500 - 5000 ppm
• maximum allowed concentration within a 8 hour working period: 5000 ppm  

The levels above are quite normal and maximum levels may occasionally happen from time to time.

Extreme and Dangerous CO₂ Levels

• slightly intoxicating, breathing and pulse rate increase, nausea: 30,000 ppm
• above plus headaches and sight impairment: 50,000 ppm
• unconscious, further exposure death: 100.000 ppm

Carbon Dioxide Standard Levels

The recommendation in ASHRAE standard 62-1989 are

• classrooms and conference rooms 15 cfm per occupant
• office space and restaurants 20 cfm per occupant
• hospitals 25 cfm per occupant