All of these symptoms may also be caused by other factors, and are not necessarily due to air quality problems. For example, environmental stressors such as improper lighting, noise, vibration, and overcrowding, or problems such as emotional stress, can produce symptoms that are similar to those associated with poor indoor air quality. Because people are different, one individual may react to an air quality problem while others have no noticeable ill effects. In other cases, complaints may be widespread. In addition to different degrees of reaction, an indoor air pollutant or problem can trigger different types of reactions in different people.
Children are especially susceptible to air pollutants like mercury.
Over the past few decades, exposure to indoor air pollutants has increased due to a variety of factors, including the construction of more tightly sealed buildings that reduce fresh air exchange to save energy, the use of synthetic building materials and furnishings, and the use of chemically-formulated personal care products, pesticides, and housekeeping and teaching supplies. Four basic factors affect indoor air quality. The HVAC system includes all heating, cooling, and ventilating equipment serving a school. Ideally, a properly designed and functioning HVAC system controls temperature and humidity to provide thermal comfort, distributes adequate amounts of outdoor air to meet ventilation needs of school occupants, and isolates and removes many pollutants through pressure control, filtration, and exhaust fans. Not all HVAC systems are designed to do all of these things.