Exploding the CTUEdit
Stan Blackwell, the special effects coordinator for the scene, explains that there are around 93 explosions going off in the scene where CTU Los Angeles is attacked. He explains that air is the main weapon used by the special effects team, with many foam walls inserted that explode from pressure from the air. He also showed the device used to blow out the windows with air, which looks violent but is very safe.
He goes on to explain that too much styrofoam ruins a shot, and so much is cut out from the walls before the explosion takes place. He demonstrates how a "squib" works - some explosive is inserted into a small hole and when it is fired it kicks a switch that releases a catch and drops whatever it is holding; in the case of this a large air vent above CTU.
Blackwell says that in most cases he leave it to the stunt coordinator, Eddy Donno, to place people in positions that will keep them safe. Donno then converses with Blackwell about positions where people will be stood during the explosion. He then explains to viewers that, with a movie, many takes can be done to perfect a shot, but with a television show there is just one opportunity, and so everything has to be right.
Blackwell and Donno, along with many other members of the 24 production staff, prepare for the big day. A final run through of the action is conducted with all stunt people and crew present. Blackwell meanwhile explains that slow-motion cannot be used on 24 as it defeats the real-time aspect that makes it unique. Therefore, on a sequence like this it needs to stay "busy" all the time. Donno and Blackwell talk about the fact that the crew have to work in the location for the rest of the year, so it needs to stay clear enough for camera dollys to fit through, but devastated enough to look like the explosion only just occurred a matter of minutes or hours ago.
The crew make final preparations for the explosion. The explosion goes ahead as planned, and Blackwell operates the button that causes the squibs to go off, leading to the air vents collapsing, the windows shattering and the various other explosions taking place. The second explosion is then prepared for, this time focusing on the glass shattering from the Director's office. Once again it went ahead as planned, and the A, B, C and D camera angles are shown separately, then the aftermath. Stan Blackwell comments that everyone was happy with how it went, so he was happy.