Most fires in the city burn throughout the game no matter how much time has passed.
The explosives that the Player has to bring to a safe distance could easily be disarmed just by pulling the cords from the explosives.
The city was infected for months, yet not every safe house had been opened up.
Throughout the game, there is a crane abutting the Tower. This is a possible way in, and not only that, but the ground level entrance is not defended in any way.