CO2 becomes dangerous at high concentrations, typically starting to cause noticeable symptoms around 1,000–2,000 ppm in occupied indoor spaces, with progressive effects as levels rise. Extremely high levels (tens of thousands of ppm) can be life-threatening within minutes to hours. Key points to know
- 400 ppm: typical outdoor/ambient level; considered normal baseline indoors with good ventilation.
- 1,000–2,000 ppm: common threshold where people report drowsiness, reduced concentration, and perceived stuffiness; ventilation becomes more important.
- 2,000–5,000 ppm: headaches, fatigue, poor concentration, and more pronounced symptoms; indicates poorer air exchange.
- 5,000–10,000 ppm: risk of more significant cognitive impairment, dizziness, and nausea; prolonged exposure at these levels is dangerous.
- 10,000–30,000 ppm: increased risk of serious symptoms like rapid breathing, confusion, and potential loss of consciousness; long or repeated exposures in this range are dangerous.
- 40,000 ppm (4%) and above: designated as Immediately Dangerous to Life or Health (IDLH) in many safety references; can cause severe oxygen deprivation, unconsciousness, and death with sufficient exposure and time.
- 100,000 ppm and higher: often cited as life-threatening or fatal with short exposure in some sources; exposure should be avoided and emergency response sought if reached.
Practical guidance
- Indoor air quality: ensure adequate ventilation, use CO2 monitors to track indoor levels, and increase ventilation if readings rise above 800–1,000 ppm, especially in crowded or poorly ventilated spaces.
- If CO2 approaches levels above 2,000–3,000 ppm, evacuate or significantly improve air exchange; consult safety guidelines for workplace limits (commonly around 5,000 ppm as an 8-hour limit in many jurisdictions).
- For general safety, treat rising CO2 levels as an indicator of insufficient ventilation rather than a direct measure of toxicity, and address air exchange promptly to prevent progression toward dangerous concentrations.
If you want, I can tailor these thresholds to a specific scenario (home, classroom, office, or industrial setting) and suggest concrete ventilation strategies and trigger points based on your space size and occupancy.
