|Quoting Bongodog1964 (Reply 7):|
The use of explosives to remove large buildings is now very much out of fashion in western Europe, high reach demolition excavators can now reach beyond 50 metres and can safely nibble away at both concrete and steel from the ground. Beyond that smaller excavators are craned onto the buildings to remove the upper floors first. Some are remotely operated. I was recently in the US and was interested to see on the news that buildings are still regularly imploded, complete with dust clouds and the leaving of huge tangled heaps of debris, which still has to be cleared with excavators anyway.
Often the people involved in the decision making process don´t have a clue what you can do with modern explosive techniques. They are prejudiced by Hollywood and also by American demolishers, who like to go for the big, sectacular bang and dust cloud (which would be a major show stopper here due to environmental rules).
Then we also have much stricter laws on explosives handling and transport due to security reasons, which give headaches to the people involved.
The basic rule in using explosives for demolitions is to use the minimum which can be used to get the job done safely (unlike military engineers, who use whatever is required to remove the obstacle plus some more to make sure).
One drawback of using hydraulic hammers to demolish massive concrete structures is that it causes lots of multiple low frequency vibrations, which can cause damage to neighbouring structures. In such a case the one big shock from the mass of a falling building is less harmfull. Also think about the continous noise going on for weeks while a big structure is being nibbled down (I´ve seen a company removing a concrete bombproof aircraft shelter at our airport using an excavator with a hydraulic hammer and "nibblers". It took them several weeks to get it done. I would have demolished the structure like an arch of a concrete bridge and cut it at the same time with explosives into neat lumps to be fed right into the breaker to separate concrete from the rebar. It probably would have taken a week or so to drill the about thousand shotholes and a day to load them with small charges, and another week to clean up after the blast. I would have made full use of the millisecond delay effect to both reduce the vibration shock and to cause massive fragmentation of the concrete, while keeping flying debris low, which´s flying away I would have prevented using special blast matts).
Another option for a massive building is to demolish it inside out with multiple small blasts, keeping the outer walls in place until the end to act as catchers for debris and dust. Not very spectacular, but efficient and clean.