A door assembly comprising: a track header constructed and arranged to be mounted with respect to an opening formed through a wall to which the door assembly is installed; a track; a fixed first door panel constructed and arranged to be fixed relative to the track closest to a door jamb, and at least two sliding door panels (18, 20) constructed and arranged to be slidably movable on the track, the sliding door panels comprising a middle second door panel and an outermost third door panel, wherein the sliding door panels are constructed and arranged to be slidably movable on the track between a closed position wherein the sliding door panels (18, 20) are extended across the track, and an open position wherein the sliding door panels (18, 20) are constructed and arranged to be in a compact, overlapping relationship with each other and the fixed door panel; a pivot mechanism constructed and arranged to enable pivotal movement of the track with the fixed door panel and the two sliding door panels (18, 20) mounted thereon, about a pivot axis from a normal configuration wherein the track is positioned such that the door panels (16, 18, 20) will cover the opening when in the closed position, to a breakaway configuration wherein the track is pivoted away from the normal configuration; and a lock arrangement constructed and arranged to releasably lock the track with respect to the track header to prevent pivotal movement of the track away from the normal configuration, the lock arrangement configured to enable the track to be unlocked with respect to the track header and enable the track with the fixed door panel and the two sliding door panels (18, 20) mounted thereon to be pivoted away from the normal configuration to the breakaway configuration; characterized in that the door assembly further comprises a drive mechanism mounted on the track header and constructed and arranged to drive the sliding door panels (18, 20) between the closed position and the open position, the drive mechanism comprising an electromechanical motor mounted on the track header such that the motor cooperates with a continuous toothed belt to slide the sliding door panels (18, 20) along the track, wherein the third door panel is connected to the continuous toothed belt by a releasable connection (54, 21). a track header constructed and arranged to be mounted with respect to an opening formed through a wall to which the door assembly is installed; a track; a fixed first door panel constructed and arranged to be fixed relative to the track closest to a door jamb, and at least two sliding door panels (18, 20) constructed and arranged to be slidably movable on the track, the sliding door panels comprising a middle second door panel and an outermost third door panel, wherein the sliding door panels are constructed and arranged to be slidably movable on the track between a closed position wherein the sliding door panels (18, 20) are extended across the track, and an open position wherein the sliding door panels (18, 20) are constructed and arranged to be in a compact, overlapping relationship with each other and the fixed door panel; a pivot mechanism constructed and arranged to enable pivotal movement of the track with the fixed door panel and the two sliding door panels (18, 20) mounted thereon, about a pivot axis from a normal configuration wherein the track is positioned such that the door panels (16, 18, 20) will cover the opening when in the closed position, to a breakaway configuration wherein the track is pivoted away from the normal configuration; and a lock arrangement constructed and arranged to releasably lock the track with respect to the track header to prevent pivotal movement of the track away from the normal configuration, the lock arrangement configured to enable the track to be unlocked with respect to the track header and enable the track with the fixed door panel and the two sliding door panels (18, 20) mounted thereon to be pivoted away from the normal configuration to the breakaway configuration; characterized in that the door assembly further comprises a drive mechanism mounted on the track header and constructed and arranged to drive the sliding door panels (18, 20) between the closed position and the open position, the drive mechanism comprising an electromechanical motor mounted on the track header such that the motor cooperates with a continuous toothed belt to slide the sliding door panels (18, 20) along the track, wherein the third door panel is connected to the continuous toothed belt by a releasable connection (54, 21).