Carbon dioxide (CO2)
At room temperature, carbon dioxide is a colorless, odorless, faintly acidic-tasting, non-flammable gas. Carbon dioxide is a byproduct of normal cell function and is removed from the body via the lungs in the exhaled air. Carbon dioxide is also produced when fossil fuels (like coil or wood) are burned.
Typically carbon dioxide is a result of human metabolism, therefore concentrations within a building often are used to indicate whether adequate fresh air is being supplied to the space. Moderate to high levels of carbon dioxide can cause headaches and fatigue, and higher concentrations can produce nausea, dizziness, vomiting, difficulty breathing, sweating, tiredness, and increased heart rate. Loss of consciousness can occur at extremely high concentrations. To prevent or reduce high concentrations of carbon dioxide in a building or room, fresh air should be supplied to the area.
The outdoor concentration of carbon dioxide is typically in rural areas ~400 parts per million (ppm) or higher in areas with vehicle high traffic or industrial activity. Before the Industrial Revolution, the global average amount of carbon dioxide was about 280 ppm. The indoor carbon dioxide level depends upon the number of people present, how long an area has been occupied, the amount of outdoor fresh air entering the area, and other factors.
Carbon dioxide concentrations indoors can vary from several hundred parts per million to over 1,000 ppm in areas with many people present for an extended period and where fresh air ventilation is limited. The amount of fresh air that should be supplied to a room depends on the type of facility and room. Ventilation should keep carbon dioxide concentrations below 1,000 ppm and create indoor air quality conditions that are acceptable to most individuals.