´óÏó´«Ã½

Aston University demolished two 1970's tower blocks on Sunday. They had to evacuate 1500 students which by a nice coincidence is also the number of charges used to blow the buildings up. You can watch footage of the explosion on the ´óÏó´«Ã½ website here. We've been following the preparations to demolish these buildings for the past few months and it's fascinating to learn what's involved.

First of all I was surprised to learn you don't put explosives on every floor. To bring down these twenty one and twenty three story buildings they used explosives on the 1st, 5th, 9th, 13th and 17th floors.

Inside the floors about half of the structure is removed to make sure the building will collapse as wanted. But the demolition team must also make sure the building will stay up on it's own even if Aston University decided to put everything on hold for a year or more.

Dark material is wrapped around the windows and concrete on the floors where explosives are used. This is to stop debris flying everywhere during the explosion, but it also makes things very spooky. Especially if you are high-up, with the wind blowing and you are surrounded by a neat spaghetti of cables running to the explosives in the walls.

Of course the lifts are removed fairly early on so there's plenty of climbing up and down the stairs for the teams involved. And they don't just prepare the building. Aston has several Victorian sewers and gas pipes on site and if the buildings collapsed all in one go then these might be damaged.

Watching the footage you'll hear three explosions. The first is the 1500 detonators going off in the two buildings. The explosives then "cook" and after a delay the explosives in the first building go off and down it comes. Six seconds later, just as it was designed to, the explosives in the second building go off and it then collapses.

The end result is four stories of rubble in two very neat piles. In fact construction work had already began on site for the new buildings to replace the towers. The marking and measuring that was already carried out was undisturbed by the demolition. The icing on the cake was the news that the one Aston family that couldn't be evacuated was apparently undisturbed by the loud explosions and the loss of a familiar perch. Yes the nesting kestrels are still happily sitting on their newly laid eggs just yards from the demolition as you can see on this .