From time to time contractors have to demolish existing structures, either completely or partially, to enable new structures to be built. This work is inherently dangerous, and if it’s not done correctly could result in the remaining structures or surrounding property being damaged, and even people getting injured or killed.
Usually, large demolition work must be done by licensed contractors, but often projects involve smaller demolition works that are tackled by less experienced people. In fact, sometimes contractors have to demolish newly completed work because the work was substandard of poor quality and didn’t meet the project specifications because the client changed their mind, or the designer made a mistake. Some of these demolitions are done with little forethought and planning, sometimes with inappropriate equipment, often done hurriedly so that impacts to the construction schedule are minimized.
Precautions before demolition
To prevent accidents it’s important that certain precautions and steps are implemented before any demolition work begins. These include:
1. Ensure all service lines and pipes have been terminated
Live electric cables are dangerous. Damaged water pipes can flood the project, or possibly leak underground undetected. Ruptured gas pipes can lead to explosions.
2. Make sure that the right structures are demolished
For example; in 2016 the wrong house in Sydney Australia was demolished. The contractor arrived at what they thought was the correct address and proceeded to demolish the house, instead of the house next door which they were supposed to demolish. A very expensive and embarrassing mistake. It pays to always double-check and also to ensure that there is adequate supervision in place.
3. Hazardous materials should be identified and where possible removed
Not only are these materials hazardous to work with but they can contaminate all of the demolished materials and parts of the construction site which can cause bigger problems and costs to clean up.
4. All permits and permissions must be in place
Many jurisdictions require demolition contractors to be licensed.
5. Check that there aren’t any restrictions
Heritage structures can’t be demolished.
6. Ensure that items that are to be salvaged have been removed
7. Protect the surrounding properties and structures from dust and debris
8. Prepare a risk assessment and safe work procedures
9. Have the right equipment and trained operators
10. Barricades
Barricade the areas where demolitions are happening and keep unauthorized people out of the area.
11. Cleaning
Clear demolished material as quickly as possible to make the area safe.
12. Plan
Plan the work so that demolitions are done in the correct sequence, therefore, the equipment can safely reach parts that have to be demolished, and so that structures aren’t left standing which is unsupported or weakened; they could collapse in an uncontrolled manner on top of people, equipment or other structures.
13. Warnings
Provide adequate warnings to those around the demolition work who could be impacted by the demolitions.
14. Dust suppression
Ensure there are adequate dust suppression systems in place to minimize dust.
15. Complete dilapidation surveys
For large demolitions, it is advisable to complete dilapidation surveys of the surrounding structures to record all existing cracks and defects. This will ensure that the demolition work can’t be blamed for damaging structures and buildings when the cracks were already pre-existing and weren’t a result of the demolitions.
Precautions before partial demolition
Often existing structures have to be partly demolished and openings cut in them. In addition to the checks above it’s also necessary to:
1. Engineer
Have an engineer check the structure to determine that the modifications won’t impact its structural integrity.
2. Structural support
As directed by the engineer, install permanent structural supports and beams, and where necessary temporary props and bracing.
3. Inspection
Not remove temporary props and supports until the replacement structures have attained sufficient strength and have been inspected by the engineer.
4. Dimensions & Drawings
Check that the areas to be removed are carefully and clearly marked out. On more than one occasion only a line has been marked and the portion on the wrong side of the line has been taken out. Doublecheck dimensions and drawings.
5. Equipment
See that appropriate equipment is used. Equipment that is too large or powerful may damage the remaining structures because of excessive vibrations and impacts.
6. Overloading structures
Not overload the structure by using equipment that is too heavy for the structure, nor should rubble from the demolitions be allowed to accumulate in heaps on, or against, the remaining structures.
7. Pre-cutting
Ensure, where possible, that areas to be broken out are pre-cut along straight lines to separate them from the remaining structure. This not only allows for neater joins and less damage to finishes but also lessens the risk of the remaining structure being damaged by vibrations and forces exerted on the parts being demolished.
8. Removing parts
Always ensure that only the parts to be broken and demolished are removed. Removing larger portions of the structure not only creates unnecessary additional work and costs, but it could also weaken the structure, resulting in structural damage or even causing its collapse.
Conclusion
Always take care when demolishing structures, no matter how minor the work is. Accidents happen easily. All demolition work is potentially dangerous. Demolition work must be properly supervised at all times.
Have you had demolition work go wrong? What happened?
