Ventilation is defined as the process of supplying air to, or removing air from, any space by natural or mechanical means. General ventilation uses the movement of air within the general work space to displace or dilute contaminants with fresh outside air. General ventilation of the workplace also contributes to the comfort and efficiency of employees because working under extreme conditions of temperature and humidity may have an adverse effect on employee productivity and health. In the last several years, a growing body of scientific evidence has indicated that the air within our working environments can be more seriously polluted than the outdoor air, even in the largest and most industrialized cities. The levels of air pollution from individual sources may not pose a significant risk to health by themselves, but most working environments have more than one source that contributes to indoor air pollution. Fortunately, there are steps that you can take to both reduce the risk from existing sources of indoor air pollution, and to prevent new sources from occurring. There are two primary causes of indoor air quality problems: indoor sources of air pollution and improper ventilation of your facility. Indoor pollution sources release gases or particles into the air and are the primary cause of indoor air quality problems. Inadequate ventilation can also increase indoor pollutant levels by not bringing in sufficient outside air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of your facility. High temperature and humidity levels can also increase concentrations of some pollutants.