An incubator for cell and tissue culture under controlled atmospheric conditions has a primary air flow control device that forms a primary, preferably laminar flow, air veil across an opening that allows access to the cells or tissue cultures disposed within the incubator. Preferably, most if not all of the air in the primary (laminar flow) air veil is recirculated, and a secondary air flow control device is used that forms a secondary, preferably laminar flow, air veil between the primary (laminar flow) air veil and a user of the incubator.