Poor indoor air quality in school facilities can detract from the health and productivity of students, teachers and other employees. Asthma--often triggered or aggravated by dust--is the No. 1 cause of chronic absenteeism in schools. Using vacuum cleaners equipped with high-efficiency particulate air (HEPA) filters to clean education institutions can help school maintenance workers combat indoor air quality problems. The filters, which capture particles through layering and brain-like folds or corrugations, enable vacuum cleaners to keep dust inside the machine rather than spreading it throughout the indoor environment. HEPA has not been without its critics, however. HEPA filters are far more expensive than standard filters, and because of the finer mesh and greater resistance to airflow, they may reduce a vacuum cleaner's suction and performance. In many uncontrolled and non-critical environments, the benefits of HEPA filtration are negated by particles entering the air from other sources, such as an open door or window. Generally speaking, though, HEPA filtration is a useful tool for school maintenance programs.