Safe CO2 Levels in PPM: A Quick Reference

Safe indoor CO2 levels are below 800 ppm for optimal cognitive performance per WELL Standard v2, below 1,100 ppm for acceptable ventilation per ASHRAE 62.1-2022, and below 5,000 ppm for the OSHA 8-hour occupational exposure limit. Outdoor air typically measures around 420 ppm.

Safe CO2 Levels at a Glance

Buildings already running CO2-based demand controlled ventilation typically set the BMS alarm threshold below the ASHRAE 62.1-2022 acceptable limit — commonly around 1,000 ppm — so facilities staff are alerted while the room is still within the acceptable range rather than only after it has been exceeded.

LevelStatus~420 ppmOutdoor baseline<800 ppmWELL Standard v2 optimal target<1,100 ppmASHRAE 62.1-2022 acceptable1,000–2,500 ppmElevated — fatigue, reduced concentration>5,000 ppmOSHA 8-hr exposure limit>40,000 ppmImmediately dangerous

What Happens Above These Levels

Between roughly 1,000 and 2,500 ppm, occupants commonly report fatigue, drowsiness and reduced concentration even though no acute health risk is present at these levels. Above 5,000 ppm, headache and nausea become more likely with sustained exposure, which is why OSHA treats this as an occupational limit rather than an acceptable indoor target for offices or classrooms.

How to Keep Indoor CO2 Within Safe Limits

Continuous CO2 monitoring, paired with demand controlled ventilation that opens the outdoor air damper as readings rise toward the 800–1,100 ppm range, is the standard approach in modern commercial buildings rather than relying on fixed ventilation rates sized for worst-case occupancy.

Why Ace Instruments

Ace Instruments has manufactured air quality and environmental monitoring instruments from its 10,000 sq.ft Hyderabad facility since 1991, with more than 1,000 installations worldwide. Every IAQ Detectors instrument referenced in this article is CE certified and produced under an ISO 9001:2015 quality system.

FAQ

Q: What CO2 ppm level is considered safe indoors?
A CO2 level below 1,100 ppm is considered acceptable indoors per ASHRAE 62.1-2022, with WELL Standard v2 setting a stricter 800 ppm optimal target.

Q: What CO2 level is dangerous?
A CO2 level above 5,000 ppm exceeds the OSHA 8-hour occupational exposure limit, and above 40,000 ppm is immediately dangerous to life.

Q: How can I monitor CO2 levels continuously?
CO2 levels can be monitored continuously with a dedicated CO2 transmitter or a multi-parameter indoor air quality monitor feeding a building management system.