<em>Until the power came back on, the only way down to the lower levels was via the stairs. The stairs were enclosed within an airtight cylinder and wound around in a spiral. To get into the stair well would require keying in an override code to the battery-powered locking mechanism - after first turning the battery on. The door would then rotate open.<br/><br/>Inside the stairwell the next obstacle would be the floor seal. Between each level was a sealed hatch that required power to hold it open It would literally "fail safe" - if the power went off (as it had thirty years ago), the hatches would all close automatically and remain that way until opened manually.<br/><br/>To open these hatches, without power, required turning a small lever in the top to release the spring loaded bolts, then phgysically dragging the hatch up and to one side. It would then need to be held there manually while passing through, because the moment it was released it would close again instantly. There were four such hatches to negociate between the hangar level and the Primary Life Support Level</em>