In the installation of lead-lined doors, many issues arise due to the lack of established standards. For instance, there is a type called a "processing window," which is a window installed in the wall between a photo studio and a processing room. It resembles a box embedded in the wall, with a partition dividing the interior into two sections. One section holds unprocessed film waiting to be developed, while the other contains already processed film. Each end of the room has a small door on either side of the wall.

The two small doors in the photo studio and the darkroom are designed to interlock. Normally, both are closed and can be opened, but if one door is opened, the other on the opposite wall is locked and cannot be opened. The purpose is to protect the darkroom staff from X-ray exposure. Over the years, we have not found a single qualified film exchange window. Most of them have malfunctioning interlocking mechanisms, lead protective doors that do not close securely, or cannot be opened.

It can be seen that, in normal circumstances, four compressed springs keep the four small doors on either side of the wall tightly closed. If one of the doors is opened, its pivot will rotate. The bamboo lever welded to this pivot pushes against its top rod, pushing it into the window on the opposite side. This pushes against the opposite top rod, causing it to tightly press against the arm on the opposite pivot. As a result, the opposite pivot cannot rotate, locking the opposite small door in place.