Demolition work:
· Construction involves putting a structure up and demolition involves pulling it down.
· The reason for demolition may be the age and safety condition of the building.
Types of demolition:
1. Manual demolition
2. Mechanical demolition
3. Demolition using explosives
1) Manual demolition:
Manual demolition involves pulling the structure down for small buildings such as single story homes.
· Hammer
· Chisels
· Milled billers
· Wracking bails
Method of manual demolition:
i. Only hand tools are used in this demolition.
ii. Lifting appliances may be used to hold larger structural members.
iii. The safe place of work must be provided where scaffolds are used to provide a working platform is it should be dismounted progressively as the building is demolished.
iv. Each main structural member shall be supported crane temporary drops while the ends are cut.
iv. A free fall of debris on the grand inside or outside the building is admitted only when horizontal distance between the points where the debris will fall and the main road is more than 6 meter.
vi. Steel structural members shall be demolished and lowered gradually to the ground (mechanical).
2) Mechanical demolition:
· Mechanical demolition involves both the pulling down and knocking down of the structure.
§ In this type, machinery's are used such as cranes excavators, bulldozers.
· This type of demolition is used for larger dangerous.
· Sometimes wrecking balls also used.
A safe method of mechanical demolition:
· Only the operator and his assistants are allowed within the restricted area of demolition (the restricted area is 6 meter).
· The cabin of the machinery should be strong enough to protect the operator against to the fall of the debris.
· Also, the front window glass of the machine shall be shatterproof and protected by a steel screen mesh.
3) Demolition ball:
o The size and use of a demolition ball shall be in occurrence with the crane manual facture recommendation.
o An anti-spin device shall be used on the hoist pro in conduction with the ball attachment.
o The machine shall be used on level ground.
a) Vertical drop:
The ball is suspended above the structure and the brake released allowing the ball to fall freely on to the structure.
b) Swinging in line with the Jib:
o An additional rope is attached to the demolition ball from a second drum on the crane and used to pull the bar forward towards the machine.
o The pulling rope is released allowing the ball to swing allowed in line with the Jib stickling the structure.
o The secondary rope is used to control the limit of the swing of the ball.
Precautions while using demolition ball:
· No workers shall be permitted in the demolition area when valuing is performance.
· The crane capacity shall be adequate for the demolition operation.
· The roof of the operator’s cabin shall be strong enough to width stand flying debris.
· When pulling over walls all steel members affected shall have been at previous.
· The weight of the demolition ball shall not exceed 50% of the cranes rated load (safe working load) SWL.
Wrecking ball:
· Wrecking ball is a heavy steel ball usually hung from the crane that is used for demolishing the large building.
· Wrecking ball weight range from 450kg from to 5400kg (max).
Using explosives:
· In this type of demolition explosives like TNT (Trinitron towline) Dynamic or other explosives are used.
· Remove the support structure of a building at the certain point. The section of the building above the point will fall down.
Precautions while demolition using explosives:
· Demolition by using explosive shall be performed by obtaining the necessary permission from the concerned authorities.
· A survey of the adjust cent building shall be conducted. If any adjust cent structure is unsafe or may become unsafe during demolition process shall not perform demolition activities until remedy’s measures like shell pilling shearing or by other ways to ensure safety and stability to adjust cent structure from collapsing.
· After blast safety precautions should be taken during the removal of debris.
· No one is permitted to return back to the blasting area unless the blasting experts advise that the operation is completed.
· When there is a possibility of severe vibrations due to the explosion seismic testing should be performed to study the effect of the vibration adjust cent buildings.
Keys to safe demolition:
· No demolition work shall be commenced unless a demolition permit is issued from the concerned department.
· Before starting and demolition work the contractor shall conduct engineering survey (by a registered professional engineer) of the structure to determine the structure layout, the condition of framing, walls, floors, the possibility of unplanned collapse of any portion of the structure.
· Prior to the commandments of any demolition the contractor shall conduct a survey for the presence of reading in buildings (In buildings may be lead pipes, sheet metal roof are may be certain lead).
· In case that explosive will be used in demolition operation specialized personal shall perform the job after obtaining the approval of the concerned department.
· If it is necessary to maintain any power, water or other utilities during demolition such lines shall be such temporary relocated and protected in case it will be affected by the demolition activities.
· A fence height is at least emotes shall be erected to enclose all demolition operation and shall be maintained during all the demolition operations and removal of debris.
· The contractor shall provide a protection 6 arrear not less than the height of building which is to be demolished and he has considered the safety of pedestrians and adjusts cent and buildings.
The process of demolition is often considered as a reversal process of building.
However, building plans and details of the buildings are often not available, either not handed over to the building by the builder or the building plans are too old to be traced. As a result, details of the specification and structural elements have to be established by subsequent survey, tests, and examination.
To carry out demolition safely and economically, a great deal of experience and skills are required. The works should be carried out by competent contractors with extensive knowledge in old building technologies and practices.
In the past, there were instances that explosives, undetonated bombs, or other
dangerous substances had been found during the demolition of basements or
removal of old wooden piles from foundations. In such cases, it is advisable to follow
the emergency procedures and report to the Fire Services Department, the Police or other appropriate authorities.
There are many safety and health issues relating to demolition works, such as –
Noise At present, concrete breaking using pneumatic breakers is the most commonly employed method in demolition projects. These breakers vary from truck-mount to hand-held. The noise level can be as high as 120 dB(A) or more. If more machines are employed to meet the scheduled programme, both the process control and location of the plant and process had to be carefully considered for the safety and health of workers working therein.
Considering the time in which the workers are exposed at a demolition site, noise hazard could be very significant. Unfortunately, engineering control seems to be very limited.
The selection of more environmentally friendly plant and breakers, suppressors and silencers on compressors and breakers, wetting of the materials, etc. should be considered to reduce the noise levels to a minimum level. In addition, earplug and earmuffs should be provided and used by all workers exposed to the noise hazard particularly to those operating noisy machines and plants.
Plant and equipment
Plant and equipment should be regularly maintained. Faulty items not only generate a high level of noise but also pose additional safety concerns to workers. Workers should report promptly and return the equipment immediately for repair. It should be taken away for service.
Personal protective equipment
Old building sites are potentially dangerous. The underground services are usually in poor repair state. Previous use of the site, such as factories, oil stations or depots, should be carefully assessed during the initial risk assessment. The underground soil may be contaminated with chemicals, flammable waste, e.g. diesels and grease, etc. and pose additional hazards to demolition workers.
Other materials, such as asbestos, asbestos containing materials, lead paint, dust or fumes, may be present, requiring proper selection of protective clothing, e.g. respirators, helmets, goggles, footwear, gloves, etc. Projecting nails, pieces of metal, etc. resulting from demolition can also cause accidents
Debris
Sections of the building must not be overloaded with debris either on suspended floors or against partition walls. Building debris should be cut into suitable sizes or loading pending removal from the site. Contaminated debris, e.g. asbestos wastes, should be packed and disposed of in accordance with existing regulations. The necessary permit and license should be applied well before the commencement of works.
Weather conditions
Strong winds or heavy rain against unsafe walls, suspended floors etc. pose unexpected dangers. Use proper temporary structures or propping to avoid
sudden collapse.
Flooding
Water build-up effectively reduces dust and/or noise but beware that it is also hazardous and can lead to failure.
Overhead cables
Excavators, cranes etc. must be checked against the height of any surrounding overhead cables to ensure safety of workers, avoid damage to plants and
disrupting the power supplies of the neighborhood, etc.
Scaffolding and hoarding
Scaffolding and hoarding must be constructed in accordance with the relevant regulations.
Public safety
The demolition site and any partially demolished buildings must be properly secured against unauthorized entry.
Dust
Should be kept to a minimum by spraying with water when necessary.
Supervision
A method statement showing how the demolition work is to be carried out should be prepared. The contractors should appoint a “competent person” who will supervise the demolition works throughout the process.
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