Carbon Monoxide
Carbon monoxide is one of the most common pollutants of indoor air. Carbon monoxide is produced whenever we breathe out. Therefore, the increase in the number of people occupying a certain building, without an increase in ventilation, is bound to concentrate air with the gas. Other sources of carbon monoxide may include heating in the furnaces. Carbon monoxide is a fast killer. With intoxicating levels of the gas, one can die immediately.