An airlock is a device which permits the passage of people and objects between a pressure vessel and its surroundings while minimizing the change of pressure in the vessel and loss of air from it. The lock consists of a small chamber with two airtight doors in series which don't open simultaneously. An airlock may also be used for passage between environments of different gases rather than different pressures, to minimise or prevent the gases from mixing. An airlock may also be used underwater… (More on Airlock)