If Twinsen gets imprisoned there, he has to talk to the nurse, and tell him that there is a loose stone, which he could use to escape. When the nurse enters the cell to inspect it, Twinsen can kill him and get out. To escape, he has to use the little window and not the main door because if he uses the main door, the supergro guarding outside the door will capture him inmediately.
After getting out from the little window on the side of the building, a soldier will ask him what he is doing there. Twinsen must answer "I was fixing the antenna", otherwise he will get captured again. Finally, he has to pass behind the supergro in a discreet behaviour.