Normal CO2 levels for offices

Some amount of carbon dioxide gas is all around us at all times and normally it's not a problem. However, in an indoor environment like an office, levels of this gas can increase as a result of poor ventilation and other problems. This can potentially cause health concerns and can also be a sign that other, more hazardous, gases are also building up.

Carbon dioxide is a colourless, odourless gas with the chemical formula CO2. It is a normal component of expired air from humans and other animals, and so is always in the air we are breathing. In fact, carbon dioxide gas makes up about 0.04 per cent of Earth's atmosphere. Carbon dioxide is also a major component of the combustion of fossil fuels such as natural gas. Below -42.8 degrees C (-109 degrees F), carbon dioxide freezes to become dry ice.

Levels of carbon dioxide in air are typically expressed in parts per million (ppm) by volume. The normal concentration of CO2 in outdoor air is between 300 and 400 ppm. Indoor levels are typically quite a bit higher, due primarily to the concentration of exhaled air from the people in the building. CO2 levels in office buildings typically range between 350 to 2500 ppm. It has been demonstrated that levels above 1000 ppm tend to result in health complaints and a general guideline is that levels should be below 800 ppm to ensure everyone's comfort.

Since the main cause of indoor CO2 levels being above the outdoor range is breathing, it stands to reason that a lot of people working in a small office building will tend to produce higher levels. However, the main culprit is insufficient ventilation. If fresh air is not brought into the building in sufficient quantities or often enough, CO2 levels will tend to build up. In rare instances, other factors such as combustion exhaust gases or dry ice can also elevate CO2 levels.

CO2 levels above 1000 ppm correlate with complaints of minor health problems such as eye and throat irritation, headache and fatigue. Interestingly, it is unlikely that CO2 is causing these problems. More likely, CO2 levels are high due to poor ventilation in the building and other more toxic gases are also building up. CO2 levels above 5000 ppm are considered an occupational hazard and can cause drowsiness and other problems. Very high levels (above 10 per cent) will result in loss of consciousness.