The 32nd floor was unfinished at the time when Hans Gruber and his men took over Nakatomi Building. John McClane went to that floor during the initial takeover. When he tried to use the phone, McClane realized that they disconnected the phone lines. After seeing Joe Takagi shot dead in the 31st floor, McClane retreated back to the 32nd floor, cursing at himself for not be able to save Takagi. Then he sees the fire sprinkler and the fire alarm nearby. He turned the alarm on to alert the authorities.