Revolving door

A revolving door is a way to enter or exit a building. In a revolving door, several panels are fixed on a central axis. The panel can then be rotated to enter or exit the building. Buildings are usually fitted with revolving doors to save energy: Revolving doors can be made to hinder airflow. This means that less heat is lost. The first to develop revolving doors was H. Bockhacker. In 1881, he registered a patent in Germany for a "door without airflow". Theophilus Van Kannel registered a patent for what he called "storm door", in 1888.^[1]

Revolving doors also have problems: Once they start spinning, they force the people to keep a certain walking speed. People who cannot keep up the walking speed may fall and hurt themselves. People in a wheelchair cannot use revolving doors. The same probably applies to blind people. Revolving doors cannot be used in an emergency: They cannot be passed at a fast speed. For all these reasons, many countries have rules that buildings must also have other doors. In hotels and public buildings, is usual to find "push" doors either side of a revolving door.

Turnstiles

Turnstile exit-only doors are often used at large sports stadia (stadiums), theme parks, and other such venues. They let people exit freely, but stop entry without payment. These doors usually work mechanically, with the door panels constructed of horizontal bars which pass through a "wall" of interlacing (interdigitated) bars. This blocks people from entering illegally through the exit.

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