The NU-620M uses an impeller and HEPA filter in both the supply module at the top of the unit as well as in the exhaust module at the bottom to turn the work zone in between into a vertical “piston of air.” The transfer station’s supply impeller at the top of the “piston” draws air down through a prefilter and propels it past a supply HEPA filter and towards the work zone to create a sterile air environment. From there, the exhaust impeller at the bottom of the “piston” pulls the downflow air through the slots in the work surface to provide allergen containment. It continues to suck all the air past an exhaust pre-filter before pushing it out an exhaust HEPA filter at the bottom of the transfer station. This “push-pull” airflow passes through a work surface divided by air grills into clean and dirty areas and a work zone configured with the deep wells and feeder holders that the Innovive™ cage changing process requires.