A duct is installed in the top area of a certain zone of the gravity flow rack chain. A duct design involves GF aluminum profile and radio frequency (RF) shielding panels. A box enters the first gate of the duct, which opens inwards. Then, it passes by scanners and exits through the second gate. If scanning was not successful, the box is returned through the second gate, which open both ways. This structure has two versions: rigid and light. The more rigid version is designed for working with heavy cargo. Also, feet can be replaced with casters to ensure convenient transportation of the structure around the shop. Before this system was introduced, the scanning was performed manually.