Investigation of the potential antimicrobial efficacy of sealants used in HVAC systems

Recent experiments confirm field experience that duct cleaning alone may no t provide adequate protection from regrowth of fungal contamination on fibe rglass duct liner (FGDL). Current recommendations for remediation of fungal ly contaminated fiberglass duct materials specify complete removal of the m aterials. But removal of contaminated materials can be extremely expensive. Therefore, a common practice in the duct-cleaning industry is the postclea ning use of antimicrobial surface coatings with the implication that they m ay contain or limit regrowth. Little information is available on the efficacy of these treatments. This p aper describes a study to evaluate whether three commercially available ant imicrobial coatings, placed on a cleaned surface that 1 year previously had been actively growing microorganisms, would be able to prevent regrowth. T he three coatings contained different active antimicrobial compounds. All t hree of the coatings were designed for use on heating, ventilation, and air conditioning (HVAC) system components or interior surfaces of lined and un lined duct systems. Coating I was a polyacrylate copolymer containing zinc oxide and borates. Coating II was an acrylic coating containing decabromodi phenyl oxide and antimony trioxide. Coating III was an acrylic primer conta ining a phosphated quaternary amine complex. The study included field and laboratory assessments. The three treatments w ere evaluated in an uncontrolled field setting in an actual duct system. Th e laboratory study broadened the field study to include a range of humiditi es under controlled conditions. Both static and dynamic chamber laboratory experiments were performed. The results showed that two of the three antimi crobial coatings limited the regrowth of fungal contamination, at least in the short term (the 3-month time span of the study); the third did not. Bef ore use in the field, testing of the efficacy of antimicrobial coatings und er realistic use conditions is recommended because antimicrobials have diff erent baseline activities and interact differently with the substrate that contains them and their local environment.