Building implosion

In the controlled demolition industry, building implosion is the strategic placing of explosive material and timing of its detonation so that a structure collapses on itself in a matter of seconds, minimizing the physical damage to its immediate surroundings.

Building implosion, which reduces to seconds a process which could take months or years to achieve by other methods, typically occurs in urban areas[citation needed] and often involves large landmark structures.

Instead, the goal is to induce a progressive collapse by weakening or removing critical supports; therefore, the building can no longer withstand gravity loads and will fail under its own weight.

[citation needed] One of the earliest documented attempts at building implosion was the 1773 razing of Holy Trinity Cathedral in Waterford, Ireland with 150 lb (68.04 kg; 10.71 st) of gunpowder, a huge amount of explosives at the time.

Benefiting from the availability of dynamite, a high-velocity explosive based on a stabilized form of nitroglycerine, and borrowing from techniques used in rock-blasting, such as staggered detonation of several small charges, the process of building implosion gradually became more efficient.

[citation needed] Following World War II, European demolition experts, faced with huge reconstruction projects in dense urban areas, gathered practical knowledge and experience for bringing down large structures without harming adjacent properties.

The October 1994 demolition of the Sears Merchandise Center in Philadelphia, Pennsylvania drew a cheering crowd of 50,000, as well as protesters, bands, and street vendors selling building implosion memorabilia.

The explosion during the initial demolition attempt was not contained on the site and large pieces of debris were projected towards spectators 500 m (546.81 yd) away, in a location considered safe for viewing.

[9] The Hanford Site Buildings 337, 337B, and the 309 Exhaust Stack, built in the early 1970s and vacated in the mid-2000s due to deteriorating physical condition, were safely razed by explosive demolition on October 9, 2010.