In the episode, Lockdown. The blast doors descend, sealing off the living quarters from the rest of the hatch.
The chronology is:
- Garbled female voice and static is heard over the loudspeaker.
- Voice became clearer and was clearly a countdown.
- At the end of the countdown, the blast doors descend (but not in unison)
- After the countdown timer runs out, lights go out, black lights come on, revealing a map on the back of the door to the dome.
- After the countdown timer runs out, things go back to normal and the doors open. It's not clear whether the button was pushed (though the Henry Gale imposter claims he did push it.)
Theories
It's not clear what caused this incident, it's also not clear how often they occur. They might be:
- Random (as speculated by Locke
- Related to the Supply drop procedure, which occured around the same time, perhaps to ensure that hatch residents don't leave during the drop.
- For their safety?
- So they don't see the plane?
- Punishment for not pushing the button in time a few days earlier.
- Somehow initiated by the Henry Gale imposter as retaliation for his treatment