OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 30 Demolition

Section 421 Dismantling buildings

Subsection 421(a)

This is one of the very few requirements in the OHS Code that addresses protection of the public as well as worker safety. The intent of the requirement is self-evident.

Subsections 421(b), 421(e), 421(f) and 421(g)

All structures are loaded in some way or other e.g. by external loads of various kinds, the weight of the structure itself, etc. The various parts – or in the case of framed structures, the members – transmit these loads to the foundations. In the complete structure the forces and reactions balance one another and equilibrium is achieved. The removal of a load-carrying member may unbalance the forces in that part of the structure, upset the equilibrium, and cause collapse.

In general, it is a sound rule to demolish in the reverse order to that used for construction. However, a deliberately engineered collapse, or a mechanical process, such as the use of demolition balls, pusher arms or explosives, may sometimes be the quickest and most economical way of demolishing some structures. Such work must always be carried out under expert supervision and measures taken to prevent injury to personnel or property.

Consideration should always be given to the following:
(a) Can the proposed method lead to sudden or uncontrollable collapse of the part in question? If so, what alternative method can be used to allow the work to be carried out under control and in safety?
(b) Is the member helping to support any other parts of the framed structure not intended to be demolished in this particular operation? If so, what measures will be necessary to prevent possible collapse of those other parts?
(c) Are arrangements made for the proper use of temporary struts, braces, shores or guy ropes to control temporary instability or sudden springing of the structure?

Subsection 421(c)

The release of forces in structures where tensioned cables or bars have been used may produce unpredictable reactions. Information about the design and construction of the building should be obtained prior to demolition beginning. Demolition procedures must be prepared and supervised by a professional engineer who is at the work site to control and supervise all related work.

Subsection 421(d)

This subsection is necessary to protect workers from falling material or the collapse of any portion of the structure.