Some models have a vacuum release in the bottom edge of the door. This speeds up equalization of the air pressures, permitting successive door openings.
Some models do not incorporate a vacuum-release device. If they have a good airtight gasket seal and the freezer is in operation, the door cannot be opened the second time when two door openings are required in quick succession. This is due to a difference in air pressure between the freezer interior and the room atmosphere. Opening the door the first time results in spillage of cold air from the freezer. This cold air is replaced by warm air. When the door is closed, this warm air is cooled, reducing its specific volume, thus creating a vacuum. Leaving the door closed for about 1 and 11/2 min will allow the air pressure to equalize.