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 is non-toxic at low concentrations, air containing 10% to 20% CO2 concentrations by volume are immediately hazardous to life by affecting control of nervous system (dizziness, confusion, drowsiness, headache, and unconsciousness), failure of respiratory muscles (causing shortness of breath), visual impairment, skin sweating, and a change in the pH of the blood stream, etc.