In house hygiene as applied to industrial processes usually refers to factories where foods, beverages and pharmaceuticals are produced. In these facilities a high level of in-plant hygiene must be maintained to protect the safety of the product and the health of operators. This is often referred to as achieving BMP – Best Manufacturing Practice. In such premises regular wash down of the equipment, the walls, ceilings and floors will be needed. An air hygiene standard of 1mg/m3 will be aimed for and if this is achieved the wash downs can be undertaken less frequently. Identification of the location and sources of the airborne contaminants followed by the design, installation and maintenance of a system of hoods, enclosures, ductwork and filtration is the key to achieving the targeted hygiene standard consistent with BMP.