DESIGN CRITERIA FOR A CONTROLLED DEMOLITION (IMPLOSION)

For an uncontrolled demolition (terrorist attack) explosives are detonated external to a structure primarily but not always. On occasions the terrorist attack is internal to a structure which can also cause the building to collapse. With a controlled demolition (implosion), explosives are always used internal to a building. A building is imploded within its’ own design footprint but because of adjacent structures inhibiting it’s fall the building might have to be imploded and collapsed outside of its footprint. An oddity is the implosion of a chimney stack. Chimney stacks because of the physics involved can, whilst collapsing, break into two separate pieces which causes concern as the trajectory of fall can then become uncontrollable. Several conditions need to be addressed prior to a demolition as follows: • Is space available to accommodate the debris pile loose volume generated by the implosion? • Is the minimum charge weight of explosives being used? • Will the falling structure cause fragments to impact adjoining structures or can the fragmentation be contained? • Has consideration been given to dust control? • After considering structural details of the building does the structure lend itself to collapse through implosion or should the building be demolished by mechanical means? and • Does the demolition by implosion prove to be more economical and safer than mechanical means? A successful demolition occurs if the conditions above are appropriately addressed and executed. The alternative is to not follow the appropriate conditions and so face three failures that have occurred over the last 20 years in Australia.