The invention relates to a user access port for a controlled atmosphere apparatus comprising a porthole extending through a wall; a sealing assembly comprising a first sealing means and a second sealing means for maintaining a sealing barrier across the porthole, whereby the first sealing means comprises a first closure member that is adapted to at least substantially seal the porthole when arranged in a closed position and allow user access to the porthole when arranged in an open position; the second sealing means is mounted so as to extend at least substantially across the porthole and comprises a sealed access member and a second closure member, whereby the sealed access member comprises a user access aperture having a peripheral edge adapted to form a sealing contact with an arm of a user when an operator extends his arm through the user access aperture and whereby the second closure member is adapted to at least substantially seal the user access aperture when arranged in a closed position and at least substantially open the user access aperture when arranged in an open position. The invention further relates to a controlled atmosphere apparatus comprising one or more user access ports, a sealing assembly for a user access port and a method of replacing a sealing means of a user access port.