A revolving door typically consists of three or four doors that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure. To use a revolving door, a person enters the enclosure between two of the doors and then moves continuously to the desired exit while keeping pace with the doors. Revolving doors were designed to relieve the immense pressure caused by air rushing through high-rise buildings (referred to as stack effect pressure) while at the same time allowing large numbers of people to pass in and out. They are also energy efficient; they act as an airlock to prevent drafts, decreasing the loss of heating or cooling for the building as compared to a standard door.
Construction
Around the central shaft of the revolving door, there are usually three or four panels called wings or leaves. Large diameter revolving doors can accommodate pushchairs and wheeled luggage racks - such large capacity doors are sometimes H-shaped to split the circle into only two (hence larger) parts. Some revolving door displays incorporate a small glass enclosure, permitting small objects such as sculpture, fashion mannequins, or plants to be displayed to pedestrians passing through. Such enclosures can either be mounted at the central pivot, or attached to the revolving door wings. The wings of revolving doors usually incorporate glass, to allow people to see and anticipate each other while passing through the door. Manual revolving doors rotate with pushbars, causing all wings to rotate. Revolving doors typically have a "speed control" (governor) to prevent people from spinning the doors too fast. Automatic revolving doors are powered above/below the central shaft, or along the perimeter. Automatic revolving doors have safety sensors, but there has been at least one fatality recorded. Skyscraper design requires a means of draft block, such as revolving doors, to prevent the chimney effect of the tall structure from sucking in air at high speed at the base and ejecting it through vents in the roof while the building is being heated, or sucking in air through the vents and ejecting it through the doors while being cooled, both effects due to convection. Modern revolving doors permit the individual doors of the assembly to be unlocked from the central shaft to permit free flowing traffic in both directions. This feature, called breakout or break away, is typically used only during emergencies, or to admit oversize objects. The most effective method for this is the "bookfold" design, which allows all three or four wings to be broken away together. Normally, the revolving door is always closed so that wind and drafts cannot blow into the building, to efficiently minimize heating and air conditioning loads. In right-hand traffic countries, revolving doors typically revolve counter-clockwise (as seen from above), allowing people to enter and exit only on the right side of the door. In left-hand traffic countries such as Australia and New Zealand, revolving doors revolve clockwise, but door rotations are mixed in Britain. Direction of rotation is often enforced by the door governor mechanism, or by the orientation of the door seal brush (weatherstrips).
Security
Revolving doors can also be used as security devices to restrict entry to a single person at a time if the spacing between the doors is small enough. This is in contrast to a normal door which allows a second person to easily "tailgate" behind an authorized person. Extreme security can require a particular type of bullet-resistant glass. Sometimes a revolving door is designed for one-way traffic. An example is the now-common usage in airports to prevent a person from bypassing airport security checkpoints by entering the exit. Such doors are designed with a brake that is activated either by mechanical means or by a sensor should someone enter from the incorrect side. The door also revolves backwards to permit that person to exit. More sophisticated electronic brakes also notify security of attempts to enter the door from the wrong side.
Turnstile exit-only doors are also often used in subways and other rapid transit facilities to prevent people from bypassing fare payment. They are similarly used at large sports stadiums, amusement parks, and other such venues, to allow pedestrians to exit freely, but not to enter without paying admission fees. These doors usually work mechanically, with the door panels constructed of horizontal bars which pass through a "wall" of interlacing (interdigitated) bars, allowing the door leaves to pass through, but blocking people from illegally entering through the exit.
Emergency use On November 28, 1942, the Cocoanut Grove, a popular nightclub in Boston, Massachusetts, went up in flames, killing 492 people. One of the main reasons cited for the large number of casualties was the single revolving door located at the entrance. As the mob of panicking patrons attempted to use the door as an escape it soon became jammed, trapping victims between the door and the crowd pushing towards it. As a result, many people died from smoke inhalation. In 1943, it became a Massachusetts state law requirement to flank a revolving door with an outward swinging hinged door or to make the revolving door collapsible (so it becomes a double partition collapsing at 180°), allowing people to pass on either side. American revolving doors are now collapsible. Some jurisdictions require them to be flanked by at least one hinged door, or this is a common practice. For example, the Ontario Building Code 3.4.6.14. asserts that a revolving door needs to "(a) be collapsible, (b) have hinged doors providing equivalent exiting capacity located adjacent to it".
History
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