The federal building blows up- in The X-Files (1998)
Early in The X-Files - the movie version of the popular TV-series - agents Mulder and Scully investigate a bomb threat and discover an explosive device in a building. The site is evacuated, the agents get away at the last minute, and the bomb blows up.
The carefully planned sequence would tell this story in a few precise shots.
Obviously a real building in the middle of downtown LA (doubling for Dallas) couldn't be blown up, so a model was constructed instead. Or rather, sections of a model was constructed and attached to a scaffold. There was no need to build the whole building since the backside wouldn't be seen anyway.
The final model stood 27 feet tall, 35 feet wide, the equivalent of 1:8 scale, and was built by Hunter/Gratzner Industries. It was surrounded by blue screen material, so the whole thing could be extracted and later combined with live action plates, shot on location.
Every floor in the building was carefully dressed with miniature desks, file cabinets, furniture, and stacks of government papers, all in the proper scale. Additionally, each floor was rigged to collapse on cue, at various predetermined points. To achieve the proper scale, the explosions were shot at four times normal speed.
For the down angle, where a big fireball races up towards the camera, each floor had to break at the exact right time - quite a feat, since the whole event would last a second in real time. For the wide view other floors had to collapse in cue with the giant dust cloud. Notice the blue screen covered miniature trees, used to make sure the smoke would interact properly with the real trees on location.
Live action street elements and a digital matte painting of Dallas completed the illusion for the two explosion shots. Finally an aftermath version of the model was needed for the post-explosion shot, where the agents carefully approach the building again. This time the actors were shot with a green screen and a motion controlled camera on location, and the move was repeated on the model. Blue Sky / VIFX assembled the sequence, under visual effect supervisor Mat Beck. A beautiful, utterly convincing sequence.
Turns out: The magic is out there, you just have to know where to look. And that's why they put the "eye" in FBI.