04 case studies on demolition.pdf

Case Studies on Accidents

Relating To Demolition Works

Chan Yew Kwong

Deputy Director, Construction & Equipment Safety

OSH Specialist Dept, OSH Division

® All Rights Reserved

Agenda

• Case studies

• Overview of legal requirements pertaining to demolition works

• CP 11 – Code of Practice for demolition

• Asbestos – Health hazard in demolition works


Brief Description of Work

1) The work involved the demolition of 12 blocks of low rise

buildings.

2) It was raining heavily and the wind was strong prior to the

incident.


Brief Description of Incident

Collapse of scaffold hoarding


Brief Description of IncidentHole in the ground indicating the

position of a wall tie which was

fixed as an anchorage prior to the

collapse of the hoarding

How the wall ties looked like

at other unaffected areas


Key Findings

1) There were 2 types of PE-endorsed designs for the anchorageof the hoarding

– one for solid ground, the other for concrete ground.

2) The span of scaffold hoarding that collapsed was not erected in

accordance with the PE’s design.

3) Wall ties were used as a form of anchorage on the road asphalt

surface instead of concrete block footings.

4) The anchorage distance from the hoarding base was also too

close.


Lessons Learnt

1) Incident could have been prevented if the hoarding and its

anchorage system were constructed according to the PE’s

design and drawings.

2) The contractor should appoint a competent person experienced

in the hoarding erection to supervise and control the work on site.

3) The condition of the hoarding should be inspected on a regular

basis, especially after incremental weather conditions.



1) The work involved the demolition, removal and replacement of

2 combined cycle plants in a power station.

2) Prior to the accident, the demolition of the embedded cooling

water stub pipes was being carried out. This was the last of

the 4 sets of cooling water stub pipes to be demolished.


Brief Description of Accident

This section of the

concrete block &

steel pipe was pulled

out from the hole

before lunch

Concrete block still stuck

in the hole. Deceased

was standing inside the

hole hacking the concrete

prior to the accident


Brief Description of AccidentThis section of the concrete

gave way and struck the Deceased


Key Findings

1) During the demolition of the embedded cooling water stub pipe,

there were no continuing inspections made by a designated

person to detect any hazard resulting from weakened or

deteriorated floors or walls, or loosened materials.

2) The weight of the top portion of the concrete aggravated by the

vibration generated by the pneumatic breaker used in the hacking

process probably caused the sidewall of the concrete to crack

and eventually gave way, resulting in the top right corner of the

concrete falling onto the deceased.


Lessons Learnt

1) Accident could have been prevented if the worker has carried

out the hacking work by standing in front of the block of the

concrete to be hacked instead of going inside the pipe hole

and worked under the block of the concrete to carry out the

hacking.

2) A designated person should be appointed to carry out continual

inspection while the demolition of the embedded cooling water

pipe was being done to detect any hazard resulting from the

work.

3) Appropriate training and briefing should be provided

for workers before they can be deployed to carry out such

demolition works.



1) The work involved the expansion of a road junction and a bridge.

2) Prior to the accident, about 30m of the existing roadside drain

and its metal railings beside the footpath were demolished. The

contractor was in the process of demolishing some metal railings

beside the footpath.



One piece of 3m long metal

railing was demolished first

30m of drain and railing has been

demolished prior to accident



When the hacking started this end of the railing

swung towards the direction of the footpath with

great force and speed



Deceased was

standing here

This metal leg of the railing

panel was badly corroded

This metal leg did not

break off completely


Key Findings

1) When the hacking started, it caused the end of the railing with the very badly corroded metal leg to swing with great force andspeed. The force could be due to the vibrations transmitted from the concrete breaker to the railing panel.

2) No Safe Work Procedure for the demolition of railings.


Lessons Learnt

1) Accident could have been prevented if gas cutting was used to

cut the two metal legs and remove the railing panel instead of

using concrete breaker to hack the footings.

2) No worker should be in the vicinity of the operation zone of the

excavator mounted with hydraulic breaker when it is in operation.

3) The contractor should appoint a competent person experienced inthe type of demolition work concerned to supervise & control thework on site.

4) Appropriate training and briefing should be provided for workersbefore they can be deployed to carry out such demolition works.



1) The Work involved addition and alteration works to an existing

school.

2) Prior to the accident, the deceased was demolishing a partition

brick wall inside a toilet.



Partition wall that

has collapsed and

hit the Deceased

on his head


Key Findings

1) Deceased had hacked the partition wall from the bottom section

using a 10-pound hammer.

2) The partition wall was simply resting on the ground and abutted

against the adjacent main wall. There was no interlocking joint

between the partition wall and the main wall.

3) As-built detailed drawings of the toilet walls were not made

available to the contractor prior to the hacking work.

4) In-house demolition procedures were not effectively implemented.


Lessons Learnt

1) Accident could have been prevented if the wall was demolished

in the reverse manner to that of its construction, i.e. the partition

wall should be hacked from the top section and extended down

progressively so as to maintain its structural stability.

2) Workers should be grouped in teams of two or more when

carrying out demolition works.

3) The contractor should appoint a competent person experienced in

the type of demolition work concerned to supervise and control

the work on site.

4) Appropriate training and briefing should be provided for workersbefore they can be deployed to carry out such demolition works.


Legal requirements for demolition works

Workplace Safety & Health Act 2006

• Every occupier is to take, so far as is reasonably practicable, such measures to ensure that: > the workplace;> all means of access to or egress from the workplace; and> any machinery, equipment, plant, article or substance kept in the workplace,are safe & without risks to health to every person within those premises (including members of public)

• Every employer is to take, so far as is reasonably practicable, such measures as are necessary to ensure the safety and health of his employees at work



WSH (Risk Management) Regulations 2006

• Employers / Principals of workplaces are to:

– Assess risk to workers arising from work before work commences

– Eliminate the risk where possible, or if not take measures to control the risk such as:

• (i) Substitution

• (ii) Engineering controls

• (iii) Administrative controls, including safe work procedures

• (iv) Provision and use of suitable personal protective equipment

– Establish Safe Work Procedures

– Communicate the risk & control measures to the workers



WSH (Construction) Regulations 2007• All worksites to implement an OSHMS – audit/review once

every 6 months

• Convene regular site co-ordination meeting :- to coordinate various works carried out on site;

- ensure measures are taken for works to be carried out sequentially and systematically with due regard to the safety and health of workers

- to be presided by the project manager

• Implement permit-to-work system

• Appoint WSH co-ordinator (contract sum less than $10m)

• Safety and health training for workers and person who oversees or supervises any work processes



WSH (Construction) Regulations 2007

PART X -DEMOLITION

Regulation

69. General duty on occupier

70. Preparation of demolition work

71. Protection of adjacent structures

72. Removal of load bearing structures

73. Demolition of walls, partitions, etc.

74. Access to floor

75. Barricades, catch platforms and warning signs

76. Mechanical method of demolition


• The building or structure should be examined and, if necessary, tests carried out, to determine its condition, and whether constituent materials have deteriorated in strength which could result in instability arising due to a particular demolition process.

• The demolition contractor is required to appoint a competent person experienced in the type of demolition work concerned to supervise and control the work on site.

• A programme should be drawn up in which the proposed sequence and methods of operations are clearly indicated.

CP 11 – Code of Practice for Demolition


• The demolition contractor should be responsible for ensuring that plant and equipment is maintained in good working condition at all times.

• All workmen, during demolition work, shall wear adequate protective clothing and where appropriate helmets, goggles, safety footwear, safety harness and industrial gloves.

• Buildings and other structures should generally be (hand demolition) demolished in the reverse order to that of their construction.

CP 11 – Code of Practice for Demolition

04 case studies on demolition.pdf

Documents

brief description of

block of theconcrete

concrete ground

hoarding erection

hoarding base

concrete block footings

hacking work

wall ties