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Airlocks serve as the entrance and exits to spaceships, whether it is docking with another ship or for extravehicular activity (EVA), without compromising the atmosphere of a spaceship. They consist of a hyperbaric chamber with a pair of airtight doors, one allowing access to the ship's interior and the other to the vacuum of space. The chamber can be pressurized and depressurized in a controlled fashion. A Viper launch tube constitutes a form of airlock with additional features for the rapid deployment of Vipers.
Ejecting a person from an airlock or launch tube is a common and easy execution method ("Flesh and Bone", "Collaborators") and the phrase "throwing someone out of an airlock" has gained some notoriety due to Laura Roslin's preference for spacing Cylon agents in this manner ("Flesh and Bone", "Lay Down Your Burdens, Part II"). Much to Gaius Baltar's dismay, Roslin suggested throwing Hera out an airlock, in order to prevent the Cylons from obtaining the hybrid (Downloaded). Although seen as a quick execution, whether it qualified as humane is open for debate given Adama's comment that human survival is possible for up to a minute in a vacuum. (A Day in the Life)
Airlocks on Galactica have an observation booth from where a depressurized airlock can be safely monitored by personnel. It has the same layout as the launch tube control room.
Cally and Galen Tyrol were trapped in airlock 12 on deck 14, after the computer automatically shut the blast doors due to pressure loss in the airlock. In order to affect a rescue, the two had to be technically airlocked when the bulkhead was blown and the two crewmembers were blown into a nearby Raptor, surviving the experience although Cally was seriously injured. (A Day in the Life)
During Gaeta's Mutiny, Tyrol directs Apollo, Starbuck, Roslin and Baltar to go to the Secondary Storage Bay and get Admiral Adama and Colonel Tigh there if they can and that he has arranged for a way off the ship there. Its revealed that that location posseses an abandoned and forgotten airlock that was damaged in the Battle of New Caprica but brought back online by Tyrol for his plans. There, Tyrol has a Raptor from the Rebel Basestar dock to pick up the group and take them to the baseship for saftey. Roslin and Baltar leave via the Raptor while Tigh and Admiral Adama stay behind to defend the airlock and retake the ship before being recaptured, while Tyrol, Apollo and Starbuck use the vents to escape into the ship. (The Oath, Blood on the Scales)
During the Battle of the Colony, Galactica crashes its nose through the side of The Colony, allowing a strike team made up of Marines and Rebel Centurions to enter the Colony through one of Galactica's bow airlocks. After rescuing Hera Agathon with help from Boomer and meeting up with Starbuck's team, the rescue team returns to Galactica through the airlock. (Daybreak, Part II)