To maintain structural integrity, the structure must be pressurized such that the internal pressure equals or exceeds any external pressure being applied to the structure (i.e. wind pressure). The structure does not have to be airtight to retain structural integrity—as long as the pressurization system that supplies internal pressure replaces any air leakage, the structure will remain stable. All access to the structure interior must be equipped with two sets of doors or revolving door (airlock). Air-supported structures are secured by heavy weights on the ground, ground anchors, attached to a foundation, or a combination of these.