Session 16 Demolition Works

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Session 16

Demolition Works

OSH5063EP(PRS3607)

Workplace and Work Equipment Hazard

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Demolition

There will always be a need for demolition as

buildings deteriorate with age to the point of

instability and where existing buildings must be

replaced in the cause of redevelopment.

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Demolition

Demolition is one of the most dangerous activities

undertaken in the construction industry.

An accident on demolition work is much more likely

to be fatal and serious than on other construction

work.

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Demolition

There are various causes attributing the accidents

in demolition works:

structure to be demolished without adequate

background information;

incompliance with planned work method;

site management staff and operatives acquire

insufficient training to identify the hazards, etc.

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Demolition

Generally, demolition works should be planned in

similar details to other building operations or works

of engineering construction.

To ensure safety and health of workers, a safe

system of demolition work need to be estabished

and implemented carefully.

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Pre-demolition survey

Prior to demolition taking place, it is necessary to

collect data as well as on-site surveys on the

building to be demolished, in order to establish the

safe system of work.

The system will be determined by a pre-demolition

survey undertaken by a competent person,

appointed by the employer.

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The pre-demolition survey should identify:

The nature and method of construction of the

building;

The arrangement of buildings adjacent to that for

demolition and the condition of this adjoining

property;

The location of underground services, e.g. water

mains, electricity cables, gas pipes, drains, sewers,

telephone cables, etc;

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The previous use of premises, e.g. for the storage of

inflammable substances;

The presence of dangerous substances, e.g. asbestos

lagging;

The method of bonding of the main load-bearing

walls;

The system of shoring or other supports necessary

during demolition;

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The presence of cantilevered structures, their form of

construction and the nature of the danger;

The presence of basements, cellars, vaults or other

spaces affecting the structure of adjoining properties;

The potentially dangerous effects of removing

superstructure stabilizing loads from an old

basement or vault retaining walls;

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The presence of storage tanks below and above

ground, and the nature of their contents; and

The actual sequence of operations, which should

generally take place in the reverse order of building

erection.

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Pre-demolition

Before the demolition begins, a risk assessment

should be conducted to assess the condition of the

demolition works, to find out any foreseeable

hazards and to devise and adopt suitable safety

measures.

The use of a demolition hazard checklist is

recommended.

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Structural Design

To study the design of the building structure is a

very important step in the survey.

If special design such as arches, pre-stressed

reinforcement, reinforcement under tension, curtain

wall or thin shell is observed, special shoring and

demolition method should be adopted.

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Structural Design

It has to find out whether the structure is capable to

withstand the increasing load as the process

proceeds.

Temporary support and suitable method could be

devised to cope with the additional loading.

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Structural Design

The structural survey should note variation to the

original plan due to structural alterations and

additions.

Special precautions should be observed to handle

structural alteration such as external metal cages,

water cooling towers and canopies, etc.

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Structural Design

Buildings or structures may have seriously

weakened after heavily used for many years or

exposed to adverse environment.

The protective element of reinforced bar may be

corroded or the concrete may be weakened by

weathering. The structural integrity of the building

may not be as safe as its original design.

It is important to determine the structural condition

as serious deterioration may impose restrictions on

the demolition method.

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Hazards associated with the

previous use of the building

The previous use of the building may have

produced hazards requiring detailed surveys to be

carried out.

In buildings where chemicals may have been stored

and used, such as factory buildings and hospitals,

hazards associated with flammable material and

substances hazardous to health should be

identified.

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This survey should be conducted by experienced

and competent persons and should observe:

Dangerous goods stores may co-exist with boilers

or other naked flame processes in hospitals or

industrial undertakings.

Storage of hazardous substances may exist. Large

quantities of toxic or harmful chemicals may be

used in some of the manufacturing processes.

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Hazardous substances may also exist in building

material or industrial installations, e.g. asbestos

may exist in heat insulating material in boiler rooms,

lead may exist in paints, chemicals may exist in

pipes radio-active material may exist in equipment.

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Building Services

The survey should cover also the installation of

building services such as electricity, gas, water

pipes, drainage, telephone, radio an TV lines.

Written confirmation should be obtained from the

relevant authorities before commencement of the

demolition works to ensure that all known supplies

have been cut off from the site except those

required for the execution of the work.

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Safe working method statement

The precaution to combat the identified hazards,

protect workers and remove hazardous material

together with the preferred demolition procedure,

should be set out in a method statement approved

by the relevant authorities.

A detailed method statement, produced before work

starts, is essential for safe working. It should

identify problems and their solutions, and form a

reference for site supervision.

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The method statement should be easy to

understand and suitably illustrated by diagrams;

should be agreed by and known to all levels of

management and supervision, including those of

the sub-contractors.

Working method should be revised to cope with

unforeseeable hazards during the demolition

process and any changes should be made know to

all parties concerned.

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The method statement should include controlling

measures to ensure that the sequence and method

by which the elements of a building are to be

demolished must be decided before work starts.

At each stage of work a conscious appraisal of risk

of collapse must be made, the precautions worked

out and workforce properly controlled to ensure that

the precautions are put into practice.

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A comprehensive method statement should include

the followings:

Work schedule and the sequence of demolition,

especially to the sequence of cantilever structure

demolition. Design suitable demolition method to

tackle with special structures, e.g. chimney, steel

structure, pre-stressed concrete, electric cable

tower and water-cooling tower.

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Selection of suitable machinery and equipment.

Temporary shoring method and other precautionary

measures to safeguard the stability of any adjoining

and adjacent buildings.

Details of safety procedures to remove or cut off the

existing utility installations such as electrical, gas,

drains and other services.

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Details of temporary services required for execution

of work.

Details of methods for dealing with flammable

material and gases.

Details of methods to be used for the disposal of

substances hazardous to health and any necessary

protective equipment.

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Arrangement for the control of site transport used

for the removal of demolition debris.

Special precautions for entering confined space in

demolition site.

Arrangement for the protection of personnel and

public and the exclusion of unauthorized person.

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Measures to protect the environment, e.g.

controlling the emission of excessive noise and

dust from demolition.

Contingency plan for typhoon, storm, flooding, fire,

explosion and industrial accident.

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Demolition

Where possible, demolition should be carried out in

the reverse order of building erection.

No isolated freestanding wall should be left unless

judged to be secure by the competent person in

charge.

Scaffold working platforms should be used, all

refuse and debris being removed from these

temporary structures on a regular basis to avoid

overloading.

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Demolition

Debris which has accumulated behind walls should

also be removed.

Independently supported working platforms over

any reinforced concrete slabs should be

demolished.

Support for members of framed structures must be

provided before gutting, along with temporary

props, bracing or guys to restrain remaining parts

of the building.

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Demolition

On no account must operators work from the noor

being demolished, and site control must ensure that

all personnel are kept at a safe distance from the

scene of operations, when pulling arrangements,

demolition balls, pusher arms and/or explosives are

being used.

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Demolition

An on-going system of inspection must be

maintained during demolition to detect further

hazards which may result from the demolition

process, e.g. loosened materials, overloaded floors.

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Working at height

Whenever the demolition work has to be conducted

at heights, suitable working platforms or

scaffoldings should be erected.

They should be designed by a professional

engineer; erected, altered or demolished by

adequately trained and experienced workers under

the close supervision of a competent person.

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Use of machinery

If the building is to be demolished by excavator, it

must be ascertained that the structure can

withstand the weight of the excavator and the

accumulated debris. Suitable propping should be

provided if found necessary

The machine must be maintained in a safe working

condition in accordance with the Regulations.

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Use of machinery

The cab of all machines should be strong enough to

protect the operator against the fall of debris.

Machinery operator shall be properly trained in the

skill of demolition as well as safe practices so as to

maintain their level of awareness.

The excavator operator must take care not to

damage the beams and columns supporting the

excavator.

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Debris and waste disposal

No part of the building under demolition shall be

allowed to be so overloaded with debris or material

as to render it unsafe to workers employed.

Special attention must be paid to the debris at

ground level as lateral force created by the debris

and the machinery under use would cause the side

wall to collapse.

Debris and rubbish shall be cleared regularly to

avoid overloading.

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Debris and waste disposal

Debris may be allowed to fall through floor

openings but must be closely supervised. Under no

circumstances should debris be allowed to fall

outside the building.

Large pieces of debris shall be lowered properly by

cranes.

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Safe working on Demolition

sites

All precautionary measures are in place before

commencement of demolition works. Pay special

attention to the demolition of special structures,

cantilever, chimney, and pre-stressed structure.

Ensure that a professional engineer has inspected

the structure/adjacent structure and a competent

person is in charge of the operation.

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sites

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sites

Pay attention to the presence of flammable or

hazardous substances such as asbestos in

insulation, lead in paints and radio-active

substances in laboratory equipment.

In buildings where carcinogenic chemicals may

have been used or stored such as factory and

hospitals, associated hazards shall be identified by

an experienced competent person.

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sites

Check and ensure that existing floors planned to be

used are not overloaded. Otherwise, shoring should

be installed to support the floors.

Provide sufficient shoring to prevent premature

structural collapse or damage to adjacent property.

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sites

Ensure that the site is properly enclosed. Scaffold

with screen and catch-fan, and hoarding or covered

walkway shall be erected.

Erect warning and information notices.

Ensure that all ladders, cranes, cables and other

equipment are in good order.

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sites

Ensure that suitable personal protective equipment

is provided and used during operation. Suitable

anchorage points for safety belts and safety

harnesses shall be identified and assessed by

competent persons or Professional Engineers.

Adequate protection and safe access for the public

and workers are provided at all times, including

protection from dust and noise hazards.

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sites

Provide sedimentation/treatment system to prevent

silty / dirty water discharging into water courses or

public drains.

Properly plan the daily work. Complete the

scheduled work and check the stability condition of

the structure under demolition prior to leaving the

site at the end of each working day.

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Q&A

Date post:	22-Mar-2022
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Session 16 Demolition Works

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