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WITH ALL VALVES OPEN, SAM made his way back down the stairs and was surprised to find that the bottom level was filling up with water. He wanted the water to flow out into the corridor and flood the basement. Stairwells were paths for occupants to leave their floor and exit the overall structure. The direction of travel to exit the basement floor was up, to the top floor. This meant all the lower-level doors swung inward in line with the path of egress. So instead of the water pushing the door open, it was pushing it closed, and in the five minutes or so it had taken him to remove all the valves on the upper floors the water had risen halfway to the ceiling.
Sam waded in and grabbed hold of the door handle, putting his feet against the wall. He tried to pull the door open, but the wei
