The self-powered unit - by means of dry UPS battery - provides a laminar air flow of Class ISO 5 (NF, EN, ISO 14644-1) blown horizontally from the plenum towards the loading door, thus sweeping through the area where the products are stored (over the shelves and trays), maintaining a constant positive pressure within the transfer trolley, greater than the pressure in the surrounding area - thereby eliminating the possibility of any cross contamination.