The controlled properties of air, especially temperature and humidity, may be used to prevent or reduce the growth rate of some micro-organisms in manufacturing and storage areas. The particle content (dust and micro-organisms) can also be controlled to limit the risk of product contamination and hence contribute to safe food manufacture. Airborne contaminants are commonly removed by filtration. The extent and rate of their removal can be adjusted according to acceptable risks of product contamination and also in response to any need for dust control. These guidelines are intended to assist food producers in the design, selection, installation, and operation of air handling systems. Information is provided on the role of air systems in maintaining and achieving microbiological standards in food products. The guidelines cover the choice of systems, filtration types, system concepts, construction, maintenance, sanitation, testing, commissioning, validation and system monitoring. They are not intended to be a specification for construction of any item of equipment installed as part of an air handling system. Each installation needs to take account of local requirements and specialist air quality engineers should be consulted, to assist in the design and operation of the equipment.