Some of us spend a day at the zoo. Some go to the movies. And some of us – in fact, a whole lot of us – check the papers to see if we can witness a bit of history: the demolition of a building. It's no secret that we enjoy seeing things blown to smithereens, but who are the people who actually do it? What materials are used? And what type of science is involved – especially when talking about crumbling a building in the middle of a city block?
The Blasters
Before we talk about how to blow things up, let's talk about those people who make it possible. They're the blasters: a crew of explosive engineers who work together to map out and design the detonation.
Their first order of business is usually to study a building's architectural blueprints and tour the building as many times as necessary in order to fully understand the structure of each floor. At this point, the crew uses its data and past experiences with similar buildings to sketch out a plan. Many detonators also use 3-D computer models of the structure to get the most accurate plan possible. All safety precautions are accounted for very early in the project, and the team uses tools like seismographs to monitor ground vibrations and air wave pressure.
The blasters also take into account all surrounding structures and property to determine their plan, including which explosives and detonators to use. At times, they will choose to implode a structure into its own footprint – a high-risk scenario usually performed by world-renowned demo companies.
And while all blast projects are different, many have a basic idea: to think of the building as a collection of separate columns. "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," according to HowStuffWorks writer Tom Harris. "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."
So how do these guys know how this explosion or implosion is going to go? It's all about strategy.
Explore more about the science of Building Implosions at HowStuffWorks.
Bringing Down Buildings: Explosive!
Once the building has been cleared of debris and construction crews have removed non-load-bearing walls, it's time to put the plan in place. The team is strategic. Explosive placement is crucial, as the detonators have planned precisely which explosive will go off when.
"The blaster can even control the direction that a building falls by where he places the explosives and in what order they are detonated," according to an explanation on explosives.org. "For example, if the first charges are detonated on beams in the front of the building, the building will fall forward. Likewise, if the charges are detonated first on beams in the middle of the building, the building will fold in, and fall on itself. This is called implosion. Picture a chair. If you take out the front legs, the chair will fall forward."
A few of the materials and tools used to bring down buildings:
- Dynamite consists of some sort of absorbent material soaked in nitroglycerin – chemical formula C3H5(ONO2)3 – and has a high degree of stability. There doesn't need to be a lot of it; it just needs to be perfectly placed.
- RDX (cyclotrimethylenetrinitramine) is a white crystalline solid used in mixtures with other explosives. Like dynamite, it has a high degree of stability and can be used in certain points of the demo plan to give the dynamite a little extra "oomph."
- Blast caps are detonators that contain a small amount of explosive material and are connected to a fuse. When a crew member ignites the end of the fuse, the explosive material inside it burns at a steady pace. The flame travels down the cord to the detonator, setting off the primary charge.
- Delay mechanisms are often used along the with blast caps to control explosion sequences. They delay slow-burning materials that creep between the fuse and primer charge. Using these timing devices, the blasters can precisely predict the order of explosions.
- Electrical detonator fuses (also called lead lines) are more commonly used these days than traditional fuses. When current is sent through the line (via a battery, for example), electrical resistance causes the wire to heat up. This heat ignites the flammable substance on the detonator end, which in turn sets off the primer charge, which triggers the main explosives.
So now what?
The Final Countdown
The plans are all in place. The explosives are ready to go. The crew has checked and double checked the safety plan. What's left?
First comes the all clear signal for all workers to leave the site. The blaster makes the final connection to the blasting machine. A second warning goes out to the crew, and then the count down begins!
Ten... nine... eight...
Go to HowStuffWorks to find out what happens when it's time to press the "fire' button.
