CO2 exists in various concentrations in the atmosphere. The current concentration level is approximately 370 ppm (0.037%) (refer to Chapter 1), although somewhat higher concentrations to 0.06 % by volume may occur in occupied buildings [1]. It is toxic in high concentrations only. Toxicity occurs at about 10% level.

CO2 is essential for life, being a critical component in photosynthesis. Greenhouses purposely elevate CO2 levels in order to “fertilize” the plant.

Air in the lungs contains approximately 5.5% (55,000 ppm) of CO2. At low concentrations (1% by volume), CO2 causes no ill effects on humans, fauna, or flora. Although it...