Explanation:
One aspect of access control that is little talked of is airlocks. The principle is generally well under-stood. In its simplest form, the airlock is composed of two doors that are electrically interlocked in such a way that the two cannot be opened simultaneously. Airlocks are used in a variety of situations but in essence they are there to control the unwanted passage from one area to another.

Airlocks may be used to control the entry of personnel to a secure area such as a cleanroom, where dust or small particles may be a problem. Similarly if a constant temperature must be maintained then an airlock can be invaluable in reducing temperature fluctuations when doors are opened.