Airlock

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 do not 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.

Airlocks are used in UNSC spacecraft to prevent pressure loss from exposure to vacuum either due to a hull breach or the deployment of a lifepod or HEV. Halyon-class Cruisers in particular employ them as redundancy features for survivability during combat with Covenant warships.