I have some questions on the history of elevator doors, or in particular, manual hoistway doors on old passenger elevators.

I could be wrong on some of these things, as I have not found much information on this subject.

It appears that when elevators started to have hoistway doors with interlocks, the doors were usually sliding manual doors. On automatic elevators, it appears single slide side opening doors was most common. I have also seen two speed side opening manual hoistway doors, and center opening hoistway doors on manually-controlled elevators.

Later on, I would guess in the 1920s-1930s, it appeared that manual sliding doors were becoming less common, and manual swing doors were becoming more common. Later on, automatic doors started to become more common, though I have seen swing door elevators as new as the late 1970s-early 1980s.

Am I correct in this observation that manual swing doors became more common and manual sliding doors became less common? If so, why did this happen? Were manual sliding doors prohibited by elevator code at some point? Was it simply because swing doors allowed for a wider opening? I can think of a few other possible reasons.

I have also seen very old elevators where it appeared that manual swing doors were installed in place of manual sliding doors. Would this have been done due to lack of parts availability to repair the sliding doors? Or was there another reason, possibly related to why they stopped using manual sliding doors and instead started using manual swing doors?

I ask these questions because I am very interested in the history of elevators.