This Standard outlines a performance-based approach to the maintenance of ducts and components forming air-handling systems with respect to the control of microorganisms, within such systems. This approach is based on known risk factors combined with maintenance practices and compliance monitoring to create hygienic conditions within such systems of buildings.The provisions of this Standard are an alternative to the prescriptive requirements of AS/NZS 3666.2 (Clause 2.3.5) for the maintenance of air-handling systems other than those incorporating water-supplied devices such as humidifiers and evaporative coolers. This Standard addresses only the performance of maintenance programs and is to be read in conjunction with AS/NZS 3666.1 and the relevant clauses of AS/NZS 3666.2. Aspects such as maintenance manuals, records, log books, safety procedures, and the like, are as important for the application of this Standard as they are for a prescriptive approach to maintaining a clean system.