a) Order to put up barricades at Hill Street Police Station, before the 48th minute.
a.i) Now in charge of the Hill Street police station at this moment when everyone thinks that they're under siege Lt. Ray Calletano with uncertainty tells everyone "Hey I want your attention, this could be an emergency situation. So let's secure those windows and doors. "
b) In Aliens Hicks is welding the doors to the corridors where the sentry guns are placed, because the aliens are likely to start coming down them soon.
c) In Aliens, later with signs of aliens showing up on the scanners, Hicks and Vasquez are welding the doors leading to another corridor because they are sure that the aliens will be coming through them any moment as well.