Controlled demolition of a sky scraper?

Question

Sky scrapers are often found in dense urban environments. Is there a known method to controllably demolish a sky scraper with minimal collateral damage?

Answer 1

It is certainly possible, although far from easy and requires very specialist knowledge.

• First the building will be surveyed in great detail to determine how the loads are carried throughout the structure.
• As necessary internal walls and cladding will be removed to expose load bearing structures.
• The building may be weakened by partially cutting through beams, columns etc
• Explosive charges are set on predetermined parts of the building. The intent is to cut through beams and columns in a clean and controlled manner rather than pulverise the whole building. Different explosive may be used for different materials and thermite may be used to cut steel beams.
• Charges may be wrapped in ballistic textile to prevent shrapnel.
• The danger area will be evacuated and the charges fired in a precise sequence. The intent being to use the weight of the building to pull it in on itself.

If everything goes right the building should collapse onto its own footprint.

As mentioned in the comments it is easy to find videos of controlled demolitions on the internet and in many cases you can see the sequence of charges firing. The explosions themselves are usually pretty small, it's the collapse under its own weight which breaks the structure up.

Concrete buildings are generally demolished from the bottom. Steel framed buildings may need additional charges through out the height of the structure to sever beams and columns into manageable sections and stop the whole thing toppling over.

In some cases explosive demolition may not be practical or adequately safe. In this case it may be necessary to disassemble the whole building from the top down.

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Edit : A comment has raised a good point about the safety of the dust produced. Clearly any airborne dust is something you want to avoid. Also part of the preparation process should be to remove any material which would pose a potential hazard including things like asbestos, glass/glass fibre or any material heavily contaminated with anything especially nasty.

However in general it is mostly just masonry dust and isn't a massive cause for concern as long as people are kept out of the affected area untill it has settled.