Demolition is the tearing-down of buildings and other structures. You can level a five-story building easily with excavators and wrecking balls, but when you need to bring down a 20-story skyscraper, explosive demolition is the preferred method for safely demolishing the huge structure.
In order to demolish a building safely, blasters must map out a careful plan ahead of time. The first step is to examine architectural blueprints of the building to determine how the building is put together. Next, the blaster crew tours the building, jotting down notes about the support structure on each floor. Once they have gathered all the data they need, the blasters devise a plan of attack. They decide what explosives to use, where to position them in the building, and how to time their explosions.
Generally speaking, blasters will explode the major support columns on the lower floors first and then on a few upper stories. In a 20-story building, the blasters might blow the columns on the first and second floor, as well as the 12th and 15th floors. In most cases, blowing the support structures on the lower floors is sufficient for collapsing the building, but loading explosives on upper floors helps break the building material into smaller pieces as it falls. This makes for easier cleanup following the blast. The main challenge in bringing a building down is controlling the direction in which it falls. To topple the building towards the north, the blasters set off explosives on the north side of the building first. By controlling the way it collapses, a blasting crew will be able to tumble the building over on one side, into a parking lot or other open area. This sort of blast is the easiest to execute, and it is generally the safest way to go.
According to the following diagram, which part of the target building should the demolition team explode first to safely bring it down?