Movement of Airflow, Peripheral Entrainment, and Dispersion of Contaminants

Abstract

Movememt of air outwards from diffusers which have a substantially uniform discharge velocity across their whole area, is reviewed and illustrated by motion pictures. Peripheral entrainment, together with the inevitable inward dispersion of contaminants into the ultra-clean air zone, are seen to be major problems, particularly when side walls are such a restriction that they must be moved to one side or removed completely for access. A solution to both these problems is discussed, using a regressively graded discharge velocity diffusion system to provide a centrally downwards and also a radially outwards Exflow of ultra-clean air. Schlieren photography is used in a motion picture to show clearly the movement of the warm body convection currents which transport and disseminate infective bacteria from the human skin. Means of capturing, containing, and removing these hazardous emissions are discussed. Results show that when the Exflow is used together with the body exhaust and gowns then less than one colony forming unit per cubic meter of air is achievable even when people are working in that clean air zone.