General precautions during demolition
Demolition is more dangerous than construction. It is a threat to working men, the public, equipment and surrounding structures. Therefore, adequate attention should be paid to its planning and execution through various stages so as to reduce the risk of accidents and injuries to the personnel involved.
The nature of the precaution depends on the type and height of the structure, due to its demolition, the equipment used, duration, cost, and available technical expertise. Some most common precautions are necessary for all demolition work:
- Danger/Warning signs should be clearly posted around the structure as well as its doors and openings.
- Red lights should be placed on and around all barricades during dark hours.
- Watchmen should be deployed at entry points.
- PPE should be supplied to all workers and their use.
- Electrical wiring, telephone lines and water pipes should be closed while the demolition work is in progress.
- Protected walkways and trails should be provided for the use of workers and others.
Removing a member can weaken the side walls of the surrounding structure. To prevent any possible damage, the side walls should be supported until permanent protection is provided. In the case of expected threat to adjacent structure, evacuate the latter.
If a structure has been partially wrecked by fire, explosion, or other catastrophe under demolition, walls and damaged roofs must be properly shed.
If the structure to be demolished is two storeys or more than 7.5 meters high, the side road must be closed, or a side walk constructed on it. The side walk shed should be lighted to ensure safety at all times.
A toe board should be made at least 1 meter above the roof of the shed, at the outer edge and at the edge of the side walk. The roof of the side walk must be able to sustain a load of 730 kg/m.
Before a structure is demolished, paying attention to its structural design and the condition of concrete beams, columns, and walls. Pneumatic drilled hand shearing machines or gas cutting sets should be used to cut and demolish large quantities of concrete.
Hydraulic equipment used in demolition ranges from simple hydraulic breakers to highly specialized concrete crushing jaws and steel cutting shears.
Concrete up to 1 meter thick is probably cut with an abrasive water jet. At the heart of the abrasive water jet cutting system is a small nozzle in which water is pressurized to 4,200kg/cm2 and combined with solid abrasive to create a high velocity cutting jet. Cutting with water jets reduces dust and eliminates vibration and fire hazards.
Precast reinforced concrete units used in structures are usually held in position by the strength of joints or supporting walls, etc. made in the site. Before the demolition of joint structures, their supporting mechanisms must be studied. To demolish reinforced reinforced concrete, an expert’s advice should be sought.
Walls and floors
If the walls are manually demolished, this must be done by the part. Lateral bracing should be provided
If the height of the wall is more than 15 times its thickness or if it is in a weak position.
The wall on the floor of the building should not be allowed to fall as a single mass. Debris accumulated on the floor should be removed.
Structural or load supporting members on any floor should not be cut or removed until all the storeys above that floor have been dismantled and removed.
The floor can be demolished with the help of manual labor or equipment. About 300mm wide slit should be cut in the first stage for the entire length of the slab along which it is stretched. The opening should then be extended to the desired width in appropriate steps. The sheet plank is 250 mm wide and 50 mm thick and is laid at a distance of 0.4 m which should be provided for the workers. When the floors are removed no worker should be allowed to work in that area or directly below it; And such area should be barricaded. Demolition should begin only after a distance of 6.0 meters on the floor and surrounding area.
If the surface of the concrete is smooth and regular, it is cut with saws, abrasive water-jets, pneumatic/hydraulic breakers. The selection of the method is relative to the type of demolition required. Often scissors and cutters are mounted on the hoist of a hydraulic excavator to break reinforced concrete, etc. The derrick used to lower the steel structure must rest on a strong support and not be overloaded. A standard signal system should be used and workers were instructed not to drop the load, but to reduce it slowly.
Construction under demolition may include jack arches, brick cantilevers, reinforced concrete, precast concrete, pre-stressed concrete, etc. The method of demolition will vary according to the type of structure. Before cutting at the extremes heavy bulbs of wood and steel beams should be supported and then lowered to a safe place. In jack arches, the rods between the main supporting beams should not be cut until the arch or chain of arches is removed. For brick arches, expert advice should be obtained at all stages of demolition and should be supervised by an experienced person.
One of the biggest problems in any demolition work is the disposal of waste material. Generally, it is thrown near demolished structures or on public roads. Material must be thrown on the ground Taking adequate precautions. Wood or metal bangles should be used to dump waste. Want debris should also be dropped through holes on the floor without the use of a chute. Guard rails can be provided on surfaces where men stand to dump the material.
Mechanical devices for demolition include wet balls, power shovels, concrete saws, etc. Choosing the best method is a function of time, money, and the surrounding environment. The following precautions should be taken in mechanical demolition.
- The area of demolition must be barricaded for a minimum distance of 1.5 times of wall height.
- While the mechanical equipment is in operation, no workers should be allowed to enter the building,
- The device must be positioned so as to avoid falling debris.
- Mechanical equipment should not cause any damage to adjacent structures, power lines, etc.
Regardless of the method chosen for demolition or job size, the following safety precautions should be followed:
- Gas, water, electricity and other services must be properly capped in the structure before starting the demolition.
- The power or other lines required to aid in demolition must be of approved heavy duty construction and adequately protected along a known route.
- All movements of people within the structure must be on designated routes, such as through scheduled doors, ladders, or specially constructed walkways.
- Removal of debris must also follow an agreed route.
- All other openings, horizontal and vertical, must be completely closed to avoid danger from falling material. Even the openings required to remove debris should be blocked when not in use.
- Any walls or floors required to carry the excess load of stored material, or likely to be subjected to undue pressure from the waste, must be sufficiently edged to withstand the additional load.
- At no time should the debris accumulate and become too heavy for the floor. High impact loads from falling debris are another source of unsafe loading.
- The lower walls of a building are particularly susceptible to the effects of destructive loading because they are not designed for it.
- Wind loading can also be considered.
- Under no circumstances should the walls be erected overnight if they are not strong and strong enough to resist falling under air pressure. If the stability of the wall is in doubt, the demolition should continue to the nearest structural cross member; Alternatively, temporary shoring should be stacked. In general, unless specifically designed to stand higher, more than one section of a wall should be left unsupported at any given time.
- Structural member
- When a structure is demolished from above, it should support the lower level the upper level should not be cut or removed until demolition occurs.
- Care should be exercised in removing load-bearing beams and columns that tie into the walls of the party.
- Beams and columns that have been cut must be well secured with rope or chains.
- If the amount of debris is expected to be large, the surface space should be increased to dump it.
- Worker Protection
- Workers engaged in demolition work should always stand on firm grounds.
- Free ends of cut members may be required as platforms of work and should therefore be edged.
- Other hazards
- All glass and combustible materials must be removed from the structure before demolition can begin.