Abstract: A cold storage enclosure for storing of food products includes a freezer using ammonia as the refrigerant. At least one exhaust unit is provided to exhaust the enclosure in the event of a break in the refrigeration equipment which releases damaging ammonia gases. The exhaust unit is mounted to a coupling chamber unit secured to the roof of the enclosure. The chamber unit includes a tubular insulating wall support with an insulated vapor proof bearier panel secured to the inner end and a damper unit secured in outwardly spaced relation to form a coupling chamber therebetween. An interconnecting linkage is located within the chamber with the linkage coupled to the damper and including a moving arm for forced removal of the bearier panel. A heater in the chamber holds the temperature above freezing to ensure positive operation of the damper even though moisture may accummulate in the chamber and on the operator and/or linkage.