Demolition is a very precise work - and not every plant hire or construction company is willing to take on a demolition job.
Building Implosion Process
This is the funnest type of demolition work, in our opinion, because nothing is cooler than watching a massive skyscraper drop in on itself. Imploding a building is incredibly technical work and is done by only a few experts in this field in Australia. Most of the buildings where implosion is the only option exist in high-density areas surrounded by other buildings or residential areas. This is a step by step process used by the pros (and not to be done at home, kids).
Step 1: Full demolition and implosion management safety plan
It takes months to prepare for one of these massive building implosions. Here are just some of the ways contractors prepare to implode a building:
Approvals - Which requires multiple levels of government approvals, safety plans, briefings and engagement with local communities.
Blueprints and Architectural Study - On top of that is months of study of architectural blueprints of the building and site visits from the blast crews.
Deciding what explosives to use - There is also a body of work around deciding what explosives to use (which is a decision that is based on the building, type of frame, materials used in building and a general appraisal of the size and requirements of the blast needed to bring the building down).
3D Modelling - many professional blast contractors working on a major structure in a densely populated area will go to the lengths of 3D modeling the blast to fully prepare for all potential outcomes.
Fall Control - Fall control and direction of the fall is the focus on the demolition management plan - because there could be less desirable directions/ways to fell the building, given what surrounds it and the possible dust control issues
Engaging the local community - You cannot undertake a big implosion without engaging the local community and speaking to buildings body corporates and various other community groups.
Step 2: Site Preparation
On the day of the implosion, its common that the local area is evacuated, or people from surrounding areas are asked to leave their homes. Roads are blocked off, and other local safety measures are taken to control the impact to people in the local area, nearby buildings and the spread of dust and other environmental impacts. Its common that an implosion can be cancelled due to weather conditions - because high winds, rain or other complications can worsen the impacts, especially from a dust suppression POV.
Step 3: Choosing the right explosive
The most common is dynamite - which is placed into tiny bore holes in the concrete or steel columns of the building. Other types of explosive such as nitroglycerin are also a popular explosive used in building demolitions. It is usually installed on a diagonal so that when the beams are blasted, they sear and slide down in on themselves, rather than being cut on the perpendicular access and falling sideways. That is why you can often see these beams cut on the diagonal in a building that has been imploded. Sometimes differing materials - that have a faster or slower burn rate are used to assist in the timing of the detonation process, so a large and complex demolition project can often use a wide range of explosive materials.
Step 4: Explosives Placement
The blast crews will then work up the building and lay out the chosen explosive at strategic points throughout the whole building. These points are critical to how the building will collapse, and how quickly and safely it will fall in on itself. So the placement of the explosive is critical, and relates entirely to how the buildings, or sets of buildings are built in terms of their support structures. Its common that explosives are placed around the central support structures so they are wiped out first, and that loss of central structural support brings the external formations inwards.
Step 5: Explosive Timing
For most implosions, generally the contractors will try to blow out the supports in the base of the building, then take a crack at a couple of the higher floors, to destabilise the base structure and rupture the top. Obviously - blowing out the bottom struts will assist in felling the building quickly, but breaking up the upper floors insures that it falls into smaller pieces and is easy to manage when the demolition clean up crews come to remove the rubble.
Step 6: Detonate
So, experienced professionals oversee this process (and usually do so from a distance (with adequate visibility). An electrical charge is then sent down the line, which alights a flame, then the explosive materials alight and the explosion occurs, in accordance to how the timings have been set and how the professional contract has planned the building to come down. You can bring a building down in about 7 mins in total, some shorter - but that is the average (to do it safely anyway). The area needs to be clear for several hours or even days after however, as parts of the building continue to fall, and crumble. Also - the dust cloud created can linger and can be unsafe if the building had toxic materials in it (which is definitely the case of the older buildings).
Step 7: Clean Up
This process can take almost as long as the initial scoping process, many weeks, months, or even longer depending on the size of the build and the scale of the building demolished. It's not easy removing the remains of a building made entirely out of steel and concrete (which is usually the case). Especially because these buildings are generally in built up areas, so that can limit the size of the trucks used to remove the rubble. Also - there are certain construction materials, such as asbestos - that have to be treated and removed in a certain manner. Excavators, tippers and even dozers can be deployed in the clean-up phase, to organise, excavate and then remove the rubble of the building.
A lot of materials in a demolished building can be recycled and used in other buildings - especially the steel. Even crushed concrete has its applications. There are specific demolition recycling contractors that take care of the removal of materials from your site that are useful, and can even pay you a rebate on those materials as part of the blast project cost considerations.
There you have it - a full step-by-step guide on how to demolish a building. But like all incredibly dangerous and technical construction projects - don’t try this at home kids (seriously, leave it to the professionals).