When Glencairn Tower went down in November, 64 charges – 100kg of the latest explosives placed with scientific precision – brought all 17 storeys down in just five seconds.
The demolition job was unusual for two reasons. It was the first steel-structured building in Europe to be imploded and the crowd of several thousand that turned up to watch its demise may well have set a UK record for attendance at a demolition. Watching buildings bite the dust has even become something of a spectator sport: inevitably perhaps, crowds gathered to see a trio of housing blocks in Sighthill, Edinburgh go down in September and two of Aston University's student accommodation blocks tumble last spring.
Thousands also turned up to see the Deutschlandhalle arena in Berlin go down last month. In the US, local authorities have even advertised implosions. The sense in that is debatable. When the Royal Canberra Hospital, in Australia, was imploded in 1997, shrapnel and concrete chunks rocketed 2,000ft into the "safety zone", killing one spectator and injuring nine.
In November 2011, a 275ft tower being demolished at the old Mad River Power Plant in Ohio toppled the wrong way, crushing a building below, taking down electricity lines and causing spectators to run for their lives. Apparently an undetected crack in one side of the tower had pulled it in a different direction to one designated by the positioning of the explosives. That suggests just how precise calculations must be in ensuring a safe and successful implosion.
"Demolition is 50 per cent joining the dots and 50 per cent creativity, because you're dealing with a structure that's full of unknowns. If demolition was easy there would be more companies doing it. But it's an art and art isn't easy," says Mark Loiseaux, of Pheonix-based Controlled Demolition Inc (CDI), widely acknowledged as the king of demolition. It was Loiseaux who was the first to bring down decommissioned cooling towers at an active nuclear power station, Sellafield; who devised the plan for the demolition of structurally unsound buildings around the 9/11 site; who led the US mission to Christchurch after the earthquakes and whose experience of explosives more recently won CDI a contract for the elimination of weapons in post-Gaddafi Libya. His father even pioneered the whole idea of demolition by implosion.
"Architecture is about plugging info into software and watching it spit out all the specs – and I speak as a trained architect," adds Loiseaux, who might be seen in action in Glasgow in April when the first two of six 31-storey blocks of flats are due to be imploded.
"But they don't teach what we do. With demolition it's you versus the building: you have to divine what's holding the building up and that's especially hard with buildings that have technically failed but are still standing.
"The angle of repose, the volume of debris, the weather conditions, the materials, the mass and the physics of it – people have no idea how many considerations go into bringing a building down and sometimes needing to do so fast without breaking a window of its neighbours," he adds. Indeed, for these jobs, some engineers might argue that rather than blow-up a building – or "blow-down", as they prefer to call it – a more piecemeal, floor-by-floor approach is preferable. And it is in technological advances of the last five or so years that the two approaches are going head to head. In the blow-down camp, is a system called the HotShot. The skill in implosion is in knowing how much and where to put so-called "kicking" and "cutting" explosives – typically weapons-grade dynamite and Semtex respectively, the former used to take out supporting columns and dictate the direction of fall, the latter, much hotter explosive to burn through the structure – and then knowing the required millisecond differences in detonation times to get all of them to work in accord; HotShot, "the world's first auto-programmable electronic initiation system", allows for an even finer calibration of the delay between and sequencing of charges.
In the break-down camp, the Super High Reach, a £2m-a-piece mega-dinosaur of a machine, the largest in the world, weighing in at 140 tons and with a 67m-long telescopic excavation arm, on which is mounted a "hydraulic muncher that effectively eats the building," as Craig Wilson, commercial director for Technical Demolition Services, puts it. TDS, which imploded Glencairn Tower and owns one of the machines, is to send it to Newcastle to begin work on chomping down five tower blocks just as soon as "soft-stripping" – the removal of all that can be taken out of a building by hand first – is completed."In many respects demolition uses tried-and-tested methods – the explosives, for example, are modern versions of types that have been around for decades and the engineer's skill in reading a building is still paramount" says Wilson. "But technological advances are gradually changing the industry."
Certainly the rise of the machines is set to make demolition that much safer, simply by reducing the number of people needed, says John Woodward, president of the Institute of Demolition Engineers. "You don't see many of the old hand-held jack hammers at work these days," he notes. "The more inner-city projects there are – and there are more and more of them – the greater the demand for cleverer, cleaner means of demolition."
Will that mean the end of implosions? According to Loiseaux, while implosion remains the less popular approach, demand is rising as speed becomes the order of the day. Controversially, he suggests that the global industry's preference for piecemeal demolition is more a consequence of the fact that it is more lucrative. "You generate the same amount of dust breaking down a building as blowing it up, but at least implosion generates all of that dust at a known time, allowing preparation," says the man who this year imploded the Houston Main Building, in Houston, which was surrounded by 11 hospitals.
And while implosion can go wrong and requires the often tricky evacuation of an exclusion zone, breaking down only extends the opportunity for things to go wrong. This December demolition works in Southampton saw part of a building give way fall on cars on the street below.
Even without these kind of problems, demolition projects can now last as long as a decade – CDI has only recently finished one in Houston started back in 2003 – and many buildings don't seem to last as long as they used to before being taken down. "I now find that sometimes I took down the building to provide the footprint for the building we're about to take down," Loiseaux says.
Shifting housing needs, property speculation, road construction and regeneration all add up to a constant need to blow or break down: after a downwards blip in 2009, turnover for demolition companies across Europe during 2011 has increased to £1.7bn, up £156m on the year before, according to a report by industry analysts D&RI. And that means all the more opportunities to gather in crowds to witness the art of destruction in action.
Loiseaux is not keen on this trend: "Explosives and pomp and circumstance don't belong in the same boat," he says. But Woodward is more accepting of human curiosity, noting that, whatever lack of encouragement may be made, these days people come to watch regardless of the weather or time. "Some say demolition is all just big boys' toys," he says. "But anyone who thinks they can just hit a building with a big hammer and it falls down is mislead. It's what hammer you use and how you swing it that counts. That's an art that people want to see."