well, one of the Freepers had it right -- once it is determined to be an emergency scene, the officer in charge of fire command has absolute authority over the property until the scene is secured -- this is why, for suspected arson fires, we always had to post a member, 24/7, until the investigators were done, since leaving the scene constitutes "secure", i.e., relinquishing our right to the property. as long as fire command "had" the scene, no warrants are required; this goes away immediately when fire command clears the scene.
so, yes, the chief had the right to clear the man out for his own safety (which, btw, was impaired by the smoke, not the live ammo). and, yes, chimney fires are a bitch -- but it's not really common to destroy the chimney, more likely the walls, etc, that the flame spreads into. we don't have to do that as much, now that we have thermal imaging cameras to check for extension, but it must be done if it extends. it can also get into the roof through flames shooting out the top. (they make special flares to extinguish chimney fires, but it's cheaper to fill a baggie with dry powder and drop it down from the top. very cool.)