The demolition of old structures and then subsequent replacement of them with newer buildings is something that has been going on for ages now. There have been several instances in history when buildings, why even entire towns, have been razed to the ground, due to various reasons. Natural calamities like earthquakes and volcanic activities and wars have often led to the destruction of buildings, thereby making rebuilding necessary in such instances. One of the earliest instances of a building being deliberately destroyed that you can find is the demolition of the Holy Temple in Jerusalem. The temple was then rebuilt. This incident which occurred somewhere around 586 BCE is one of the earliest recorded instances when a building was demolished only to be rebuilt. From such ancient times to very latest and famous demolitions such as that of the 47 story Singer Building in New York in 1968, in order to build
the One Liberty Plaza, it is a process that is still going on.

The delicate balancing act

Quite often town planners are faced with the dilemma of whether or not to demolish old but historically significant structures in order to build newer and therefore much modern buildings. Take for example places such as the United Kingdom, which is quite densely populated. With many of the areas designated as Green Belt, there is only one way in which developers can provide structures for the population. Through demolition and then re-construction. Old factories and textile mills gradually began to take the shape of housing colonies. The scene was similar in other parts of the world too, where land became a precious commodity. In India, such examples can be found in many parts of Mumbai, where land is gold, literally. Many of the high rises in Mumbai have been constructed on pieces of land, where earlier old structures used to stand.

A lot of factors are considered before demolition of a structure. Some of them include, whether there are any valuable elements suitable for re-use and the
size of the building. It is only after a thorough analysis of these factors that it is determined as to how to demolish a particular building.

The conventional method

The entire demolition process, if one were to simplify it, would just involve disconnecting all the services and then just knocking over the walls. This would automatically cause the roof to collapse, completing the destruction of the structure. The only thing remaining to be brought down or broken up is the left over concrete. The waste would then be used to clear and sent to the nearest landfill site. This used to be the non-environment friendly method of demolition, till some time ago. The modern method though has completely changed the way buildings are demolished. In fact, the modern method of implosion, which is widely used is very controlled and  subject to a lot of planning, with particular emphasis being placed on safety.

Using bulldozers for undermining the base of walls is a technique that is used to dismantle smaller structures. The entire structure would topple over, with the fall being controlled. Specialist techniques though are needed when it comes to taller and larger structures. Chimneys and tower blocks for example,
would need specialist techniques, in order to be brought down.

Reuse

The latest approach to demolishing buildings is more environments friendly. The whole aim of the process is to reduce the amount of waste. The valuable
materials are preserved for reuse these days. This may sometimes involve time consuming brick by brick dismantling of a structure. The materials that
are reclaimed are then used for future buildings. This process, known as deconstruction can help in saving a lot of materials going to landfill sites.

If one were to carefully look at historical references then the so called modern method of deconstruction is something that is not so modern after all. There have been many instances in history when materials from old buildings have been used to build new structures such as barns and houses. The value of recycling was understood in earlier times too.

Modern technology also enables rapid breaking up of waste material, left after demolition by a machine called guillotine. The machine is capable of crushing
even the toughest of material. Once crushed the rubble, known as 6f2 crushed stone is then used as a sub-base material, widely used in the foundations of
new buildings.

Waste is nowadays disposed off either on site or offsite, using modern machinery. In a vast majority of cases, construction materials are recycled and then reused. The reuse of waste materials results in significant savings, when it comes to the overall cost of a project. What is more, the practice is also extremely
beneficial to the environment too.

Wiring, floor tiles, wooden panels, copper fittings and iron grills are some of the objects that can be used for reuse. They can be alternately sold to specialist
yards too where old artifacts and are sold too.

Large buildings

Gone are the days when a huge wrecking ball, hanging from a large crane was used to demolish the top part of tall structures. Modern technology has come up with newer techniques which are much safer and effective. Implosion using explosives is the most preferred method these days when it comes to demolition of tall structures. In certain cases, 'high reach' excavators are also used these days. Once the building is brought down to more manageable
heights, and then the demotion process becomes a lot easier and continues in the usual way.

The Singer building demolition in New York, mentioned earlier here, is one of the best examples of controlled demotion. A lot of water is sprayed during the demolition of tall buildings in order to  control the dust. This is technically known as a 'wet demolition'.

Implosion

Implosion using explosives is the preferred method when it comes to demolition of tall buildings. The method ensures that tall buildings are bought down
with as little damage as possible to the surrounding structures. The method has been used world wide, particularly in densely populated urban areas, with
great success. The collapse takes only a few seconds, with the building collapsing into its own foundation.

Using explosives for demolition of buildings is something that requires professional expertise. Getting it wrong could lead to disastrous consequences.
Flying debris could cause injuries to onlookers or even damage neighboring buildings. In certain cases, the sound caused by the implosion could break
windows in the surrounding buildings.

Safety

Bringing down a building is easier said than done.  It involves adherence to a lot of safety standards. This complicated process is therefore best handled by
competent professionals, who are trained in the job.

Since health and safety are of paramount importance, the personnel carrying out these works need to be skillful in the whole process. This is where  professional training helps. There are many certification programs available for those seeking a career in this line. Anyone aspiring to get into this line can find out about these programs and enroll in them in order to get professional training.

The process

Before any demolition process can take place, a sequence of steps ensures that it goes on smoothly and more importantly, safely. Let us take a look at the
typical order that is followed:-

• The company carrying out the demolition needs to provide all the information about how it is going to carry out the process.
• The company carrying out the demolition should carry a thorough survey of the site and identify the risk factors that are involved. They should then carry out the demolition once they have carefully analyzed all the risk factors.
• Any reputable demolition company will choose the right method for demolition of the building. They should spell out the method in a detailed statement before any demolition can take place.
• If the demolition needs to be carried out in a densely populated area, then all health hazards and potential dangers should be assessed and the people need to be informed.

Conclusion

All said and done, demolition work is something that is complicated and therefore needs to be performed by experts in the area. The aim of any demolition
is to remove an unwanted structure, in a safe manner and if possible recycle and reuse most of the old materials, during the subsequent construction to
build a new structure on the site. So, the next around you see heavy equipment carrying out demolition work, just spare a thought for all the brave professionals who are risking their life and limbs for brining us modern conveniences. They are true heroes who deserve all the appreciation in the world.

M.K.Prabhakar, Special Correspondent