If a higher degree of protection is required, HEPA filters can be very effective, provided they are tightly installed, and well maintained. Fungus can grow on HEPA filters as well as other ventilation components and, if unchecked, can actually contribute to the problem. The image at right shows a layer of actinomyces mycelium growing on a surface. Fungus or fungal spores from the outdoors can be dealt with easily, as described above. If, however, the fungus is already growing inside the building or ventilation system, the problem becomes somewhat more difficult.
Fungi require moisture for growth.
The source of the moisture must be identified and then controlled. Cooling coils, drains pans, and water pans for humidifiers are likely locations for fungal growth, especially when there is standing water. These must be treated as necessary with proper disinfectants. Some systems provide built-in UVGI lights for continuous disinfection. These components should be disassembled and cleaned with a strong disinfectant, such as chlorine, when fungal or bacterial growth is found.