Take a look at this video and watch and listen to the communications. There is a lot to learn here and these guys were under a lot of pressure. You can just feel it how they are talking and acting on the fire ground.
Just because a building is occupied does not make it inherently safe if it is on fire. The same is true for vacant buildings; just because it is vacant does not make inherently dangerous just because it is vacant. It also doesn’t mean it isn’t occupied.