The outside air entering a cleanroom is filtered and cooled by several outdoor Air handlers using progressively finer filters to exclude dust, and the air inside is constantly recirculated through fan units containing high-efficiency particulate absorbing filters (HEPA), MERV 17-20 and/or ultra-low particulate air (ULPA) filters to remove internally generated contaminants. Special lighting fixtures, walls, equipment and other materials are used to minimize the generation of airborne particles. Plastic sheets can be used to restrict air turbulence. The air temperature and humidity levels inside the cleanroom are tightly controlled. Static electricity may be controlled using ionizing bars. Cleanrooms may also have numerous seismic base isolation systems to prevent costly equipment malfunction.