Military Operations on Urbanized Terrain
Urban Building Analysis

Department stores normally have large, open interiors. Such areas permit
firing of ATGMs or man-portable surface-to-air missiles (if there are
adequate fields of fire). Often a mezzanine level with a large backblast
area permits firing down onto tanks. Steel fire doors often exist
between sections of the store. The steel fire doors are activated by
heat. Once closed, they are difficult to breach or force open, but they
effectively divide the store into sections.

http://www.biggerhammer.net/manuals/mcwp3-35.3/appi-1.pdf