There are a lot of ways to demolish a building, but when it involves a high profile building of many floors the safety of people around is very important. For a low building, ordinary sledge hammer can do the work when you employ enough labourers.
But for buildings like BOI then more technical expertise must be applied to avoid loss of lives and more properties around the area. The building in question is a peculiar one because it is surrounded all over by buildings, hence uncontrolled demolition will result in a disaster and great loss of valuable properties because the building if not well analyzed and demolished correctly may affect more valuable properties.
Excavators and wrecking balls can do the work for a fairly high building of 4-5 floors. But for an high rise you need an explosive. Explosive demolition is the preffered method for safety and efficiency , the general term is imploding of building.
To explode a building, you need to remove the support structure of the building, that is ,the structural element carrying the building will have to be the target of the explosive, when you remove the supporting element at one point the section of the building above that point will fall down on the part of the building below it and when the upper section is heavy enough , it will collide with the lower part with sufficient force to cause damage to the lower ones and just like that the crumbles goes straight down.
Blasters approach each project a little differently, but the basic idea is to think of the building as a collection of separate towers. The blasters set the explosives so that each “tower” falls toward the center of the building, in roughly the same way that they would set the explosives to topple a single structure to the side. When the explosives are detonated in the right order, the toppling towers crash against each other, and all of the rubble collects at the center of the building.
This option which I believed was used for BOI is to detonate the columns at the center of the building before the other columns so that the sides of the building falls inward. Going by the news the explosion was to be a series but one was enough to bring the entire building down, there must have been some reasons for this-
(1) When the engineers checked the plan probably the design was done in such a way that the core element of the building was at the center so they only need to strike the columns at the center for others to fall thereb causing everything to crash down.
(2) Another method could be that the engineers could have systematically weaken the center by demolishing selectively some of the columns in the building, before the major demolition. In all for sure the center of the building was weaken before it could have crashed against itself –this is common sense.
Though the building was also controlled by the cables they position around it this is secondary, the main job was done by the explosive which was planted in the building.
Blasters positions the explosives at different structural points of the building, but their decisions and methods they are using chiefly depends on where the building should fall to. Therefore it is important that the engineers carrying out such jobs requires the architectural and structural plans of the building.
There are some buildings that are required to fall sideways, but the BOI had to crumble on itself to save other properties around it even the church very close to the building was not affected after demolition.
Preliminary Measures before Blasting.
Blasting of major buildings usually involves the input of the authorities, message is sent round for people to evacuate the area for safety reasons.
Next is to begin to clear the building of debris, then demolition crews will move in and systematically weaken the building by removing the non load bearing walls -ordinary walls that are not meant to carry the building are taken out to further weaken the building and by using sledge hammer on the supporting columns (pillars) before the final blast.(though this is dangerous)
When demolishing a column, the hardest is usually the steel column, this requires more specialized explosive materials (RDX) to blast.
In Conclusion, blasters determine how much explosive material to use based largely on their own experience and the information provided by the architects and engineers who originally built the building. But most of the time, they won’t rely on this data alone. To make sure they don’t overload or under-load the support structure, the blasters perform a test blast on a few of the columns, which they wrap in a shield for safety. They tries out varying degrees of explosive material, and based on the effectiveness of each explosion, they determine the minimum explosive charge needed to demolish the columns. By using only the necessary amount of explosive material, the blasters minimize flying debris, reducing the likelihood of damaging nearby structures.