Fungal colonization and water activity studies of heating ventilating and air conditioning system insulation materials from a sick building.

Heating ventilating and air conditioning (HV AC) duct insulation in a county government facility in south Florida USA was removed because of heavy fungal infestation of the building. Samples of these materials were examined by direct microscopy and enrichment culture. Additional insulation samples were desiccated for three weeks over silica drying gel, weighed, then placed over saturated salt in water solutions at known relative humidities. At relative humidities approaching 95%, some insulation samples on an average gained 6% of their dry weight in water. The water gain at various relative humidities ranged from a low of 2 % to a high of 9.3% of the dry weight The hygroscopic nature of duct insulation and mechanical insulation in HV AC systems is most likely one of the contributing factors in fungal colonization. The porous nature of the insulation is also a contributing factor because of its propensity to trap organic and inorganic particulates. Understanding which fungi colonize these substrates and under what moisture and nutrient conditions will help design engineers make recommendations on HV AC system operational parameters including relative humidity and moisture control.