Employee complaints can be due to two types of building problems: Sick Building Syndrome (SBS), and building-related illnesses. SBS is used to describe situations in which building occupants experience acute health effects that appear to be linked to time spent in a building, but no specific illness can be identified. SBS is associated with complaints of discomfort including headache, nausea and dizziness; eye, nose, throat, and respiratory irritation; coughing; difficulty concentrating; sensitivity to odors; muscle pain; and fatigue. The specific causes of the symptoms are often not known but sometimes are attributed to the effects of a combination of substances or individual susceptibility to low concentrations of contaminants. Symptoms of SBS are associated with periods of occupancy and often disappear after the worker leaves the worksite.
In a process known as infiltration, outdoor air flows into the building through openings, joints, cracks in walls, floors, ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. The rate at which outdoor air replaces indoor air is known as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and indoor pollutant levels can accumulate to levels that can pose health and comfort problems.