Tue Nov 16, 2021
pass box in radiology
Pass Boxes were used for film-based radiology. They were installed in the walls of the darkrooms that radiology departments had for processing the film. The pass box had an outer door accessible by the x-ray technologists from outside the darkroom (so in the light of the department). They would put exposed film cassettes in the box and close the outer door. In busy departments there was usually a darkroom aide who would then open the inner door of the pass box, remove the exposed cassettes, run the films through the processor, put unexposed film in the cassettes and return them to the pass box for the technologist to pick up. Most pass boxes had double doors on the outside. This was to avoid a mixup of exposed and unexposed cassettes. The doors were clearly labeled. They also had a feature that would prevent the inner doors from opening if the outer doors were open and vice versa. This prevented light from entering the darkroom and fogging any film that might be out of a cassette but not yet put into the processor. Darkrooms did need lighting for maintenance of the processors, etc so they also had bins to hold the unexposed film. These bins were designed to reduce the risk of being left open by their doors which opened by tilting and would self-close released.
Later film-based radiography employed daylight loadable cassettes which were loaded from wall-mounted film dispensers. These film loaders used packages of film that could be placed in them in daylight for refilling. The exposed cassettes were automatically unloaded in daylight by a mechanism added to the x-ray processors. The x-ray technologist would simply place the cassettes into the receiver on the processor. The empty cassettes were then taken to the daylight loaders for refilling. There were various devices so an already-filled cassette could not be double-loaded or an empty one used to take an x-ray. These were not completely fail-safe, but they worked well.