A simple description of Downdraft ventilation would be that air is drawn down into the equipment rather than across the surface of the equipment as in Linear Ventilation. Extract ventilation is provided through ductwork to each piece of equipment. The overall volume of air required has to be balanced between individual equipment requirements and the autopsy room air changes as laid down under HBN20.
The benefits of the system are that air is drawn down into the equipment directly (see the video). Therefore the air flow around each item of equipment is in a downward direction giving protection to the users during their various work operations.