9.4 Demolition

Question 1

Pre-demolition surveys A range of pre-demolition surveys may be necessary to pull together pre-construction information for the principal contractor, including: 3

Answer 1

 Structural surveys to determine structural hazards.  Hazardous substance surveys to determine site specific hazards. For example: the presence of asbestos, the storage of hazardous materials on site, and contaminated land.  Site / environmental surveys to determine all other site specific issues such as access, ground conditions, overhead obstructions, neighbours, etc.

Question 2

Pre-demolition processes Before demolition proper can begin the following will need to be addressed:

Answer 2

 Gas, electricity, water, telecommunications and other site services need to be isolated or disconnected before demolition work begins. If this is not possible, pipes and cables should be labelled clearly, to make sure they are not disturbed.  Hazardous substances, such as asbestos, will need to be removed in a controlled manner.  Soft-stripping (the removal of non-structural components) and hard-stripping activities (the salvaging of structural components such as architectural ironwork, dressed stone, hardwood timbers, etc.) should be completed before structural demolition begins.

Question 3

Demolition - principles and techniques Structural demolition may be undertaken in accordance with the following principles: 3

Answer 3

 Piecemeal (progressive) demolition  Controlled (deliberate) collapse  Pre weakening through deliberate removal of structural components.

Question 4

There are a number of demolition techniques available which may be used in combinations or at different parts of the demolition site. The techniques broadly fit into one of four categories:

Answer 4

(1) By hand, using powered tools and often involving working at height. (2) By machine, comprising: a base machine (compact machine, high reach machine, tower crane), equipment (boom and dipper arm, for example), and attachments (hydraulic such as pusher arms, impact hammers or shears and non-hydraulic, such as demolition balls, wire ropes, drills and saws). (3) By explosive. (4) By other means, including gas expansion bursters, hydraulic bursters, expanding chemicals, hot cutting and high pressure water jetting.

Question 5

Demolition machinery and attachments As shown in Figure 9.26, demolition machinery comprises:

Answer 5

 a base machine (compact machine, high reach machine or tower crane)  equipment (for example: boom and dipper arm)  attachments (hydraulic and non-hydraulic – as shown in Table 9.8).

Question 6

The hazards presented by demolition activities will vary depending upon the techniques used. The main safety hazards include: 7

Answer 6

 Premature or unexpected collapse  Falling materials  Falling from height  Impact from site vehicle movements  Mechanical hazards associated with moving parts of heavy plant and hand tools  Fire and explosion from site services, hot work, or use of explosives  Confined spaces – cellars and voids.

Question 7

The hazards presented by demolition activities will vary depending upon the techniques used. The main health hazards include: 11

Answer 7

Chemical  Lead dust and fumes from paint removal, hot cutting, etc.  Silica dust from stone crushing or shot blasting.  Asbestos fibres from insulation materials, etc.  Gases vapours and fumes from hot cutting, chemical residues, soil contamination, organic decomposition, bonfires, etc. Physical  Ionising radiations from smoke detectors or lightning conductors or from historical uses of premises.  Noise from plant, explosive shot firing, etc.  Vibration – WBVS from driving plant / HAVS from use of pneumatic drills and breakers. Biological  Leptospirosis from contaminated surface water.  Ornithosis / psittacosis from bird droppings.  Tetanus from contaminated soil.  Food poisoning organisms from sewage.

Question 8

Precautions Irrespective of the demolition technique(s) used on a particular project, safeguards are designed around the following key principles: 3

Answer 8

 Effective work planning through site surveys and effective risk assessment.  The establishment and maintenance of safe working spaces and exclusion zones.  The development of safe systems of work, detailing appropriate precautions for the method of demolition used.

Question 9

An exclusion zone is a designated three-dimensional space from which all persons, including the public, are excluded during demolition activities. It should be designed to be adequate for the particular demolition activities. The exclusion zone is made up of four areas:

Answer 9

(1) Building/structure footprint (plan area) (2) Designed drop area (3) Predicted debris area (4) Buffer zone.

Question 10

An effective method statement will typically address: 9

Answer 10

 The sequence and method(s) of demolition detailing means for access, provision of safe working platforms and machinery requirements.  Details of pre-weakening of structures prior to demolition by explosion or pulling down.  Arrangements for protection of personnel and others through the establishment of exclusion zones.  Details for the making safe of electricity, gas and water supplies and site drainage.  Specification of temporary services required during the operation.  Detail methods for dealing with hazardous materials retained on site in machinery, pipework or tanks.  Methods for identifying the presence of hazardous substances such as asbestos on site and the methods to be used during its removal and disposal.  Requirements for personal protective equipment.  Arrangements for controlling site transport.