By HSE East Africa | Thursday Oct 18, 2018
The government of Kenya through a multi-agency team has in recent weeks embarked on demolition of over 1000 structures that were said to have been constructed irregularly. These are part of the 4,000 buildings that were earmarked for demolition in an operation to clear illegal structures from river banks and road reserves in Nairobi. Some of the most prominent buildings affected by the demolitions are the Ukay Centre in Westlands, Taj Apartments, South End Mall and The Airgate Centre in Embakasi. The team has also given notice of the intention to demolish the Seefar Apartments near the Nairobi Dam.
The demolition stage in the life cycle of a building is of the same importance as planning, design, construction and maintenance stages. The construction and demolition industry produces vast quantities of waste that for environmental, economical and social reasons are becoming unacceptable. To effectively tackle this waste issue a more effective approach must be taken from demolition and it should be economical.
The Environmental (Impact Assessment and Audit) Regulations, 2003 require that an environmental impact assessment must be concluded and approved before any project that is likely to have a negative environmental impact or for which an EIA is required under the Environmental Management and Coordination Act (EMCA) is implemented. Demolitions especially of buildings that are located next to the rivers is likely to have a negative impact on the environment and as such, an EIA should be conducted. It is therefore worrying that the National Environment management Authority (NEMA) which is part of the multi-agency team carrying out the demolitions has failed to abide by its own regulations.
Before execution of any demolition process a careful study shall be made of the structure which to be pulled down and all also of its surroundings. A definite plan of procedure for the demolition work depending upon the manner in which loads of various structural parts are supported. The demolition plan should be prepared and approved by responsible engineer and strictly followed as closely as possible, in the actual execution of demolition work.
The demolition method is selected after some pre-demolition work like surveying, removal of hazardous material and stability report. The demolition method also varies with the type of structure, structural member, demolition range, rural or urban area and frequency.
The high reach excavators with hydraulic hammer attachment used in Nairobi to bring down columns and slabs is effective but it exposes the operators and other people at the site to risks from falling objects as witnessed during demolition of the Ukay Centre and the Airgate Centre. Other methods that could be considered include use of explosives (implosion) which has been found to be the most suitable and safe for demolitions in urban areas.
There are numerous safety concerns regarding the manner in which the demolitions in Nairobi are carried. The demolition of the Ukay Centre in Westlands for instance almost turned tragic after heavy debris from the building flew right over the excavator, nearly burying it. The large crowds of onlookers that are usually present at the construction sites also presents a major safety risk since demolition work involves many of the same hazards that arise during other construction activities. However, demolition also involves additional hazards due to a variety of other factors. Some of these include: lead-based paint, sharp or protruding objects and asbestos-containing material.
Falls prevention Tips
The following safety tips by the US Occupational safety and Health Administration could help in reducing the risks of injury during demolitions.
- Brace or shore up the walls and floors of structures which have been damaged and which employees must enter.
- Inspect personal protective equipment (PPE) before use.
- Select, wear and use appropriate PPE for the task.
- Inspect all stairs, passageways, and ladders; illuminate all stairways.
- Shut off or cap all electric, gas, water, steam, sewer, and other service lines; notify appropriate utility companies.
- Guard wall openings to a height of 42 inches; cover and secure floor openings with material able to withstand the loads likely to be imposed.
- Floor openings used for material disposal must not be more than 25% of the total floor area.
- Use enclosed chutes with gates on the discharge end to drop demolition material to the ground or into debris containers.
- Demolition of exterior walls and floors must begin at the top of the structure and proceed downward.
- Structural or load-supporting members on any floor must not be cut or removed until all stories above that floor have been removed.
- All roof cornices or other ornamental stonework must be removed prior to pulling walls down.
- Employees must not be permitted to work where structural collapse hazards exist until they are corrected by shoring, bracing, or other effective means.