The top and bottom of horizontally sliding doors
shall be provided with a means of retaining the closed door
panel in position if the primary guiding means fails, preventing displacement of the door
panel top and bottom by more than 20 mm (0.8 in.] when the door
panel is subjected to a force of 5000 N (1,125 lbf) in the direction of the hoistway applied at right angles to the panel over an area of 300 mm x 300 mm (12 in. x 12 in.) at the approximate center of the panel.
The retaining means shall also withstand, without detachment or permanent deformation, a force of 1000 N (225 lbf) applied upward at any point along the width of the door panel and, while this force is maintained, an additional force of 1100 N (250 lbf) applied at right angles to the door at the center of the panel. This force shall be distributed over an area of 300 mm x 300 mm (12 in. x 12 in.).
The retaining means shall not be subjected to wear or stress during normal door operation or maintenance.