(57) Apparatus for providing a clean air zone, for example in a hospital operating theatre
or microbiological clean room comprises a housing (30) preferably mounted above the
zone and having a plenum chamber (P) and a fan and filter means (89, 52) operative
to supply air, e.g. from inlets (39), to the plenum chamber, as well as diffuser means
(40) in the form of one or more perforated plates (60, 64) arranged below the chamber
so that air flows out therethrough. In order to reliably ensure a downward and outward
air flow pattern, without the need for temperature controls or differential air velocities,
so that influx of airborne contaminants to the sterile zone is precluded, the central
diffuser area (60) is planar and successive peripheral diffuser areas (72, 73) are
arranged at increasing greater angles relative to the central area so that each increasingly
deflects the air outwards, e.g. at 5°, 15° or more, from the central downflow.
Advantageously the peripheral diffuser areas (perforate) and intervening imperforate
areas serving as deflector vanes are formed integrally as adjacent regions of specially
corrugated elongate panels (63).
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