OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 32 Excavating and Tunnelling

Section 450 Methods of protection

Subsection 450(1)

The history of fatalities associated with work in excavations is such that protective measures must be taken unless the excavation is constructed in solid rock or the ground stability is certified by a professional engineer.

Workers must be protected from cave ins or sliding materials that could cause personal injury. The listed alternatives reflect industry practice and provide an employer with some measure of flexibility in selecting the most appropriate method for the job. Cutting back or sloping the upper walls so that the remaining vertical height is no more than 1.5 metres above the floor of the excavation, installing temporary protective structures such as the trench shields shown in Figure 32.5, or a combination of these methods is acceptable under this section. The objective of the requirement is to ensure that any worker entering an excavation is protected. Figure 32.6 summarizes the options available.

Figure 32.5 Examples of trench shields

Subsection 450(2)

Subsection (1) does not apply if a trench is constructed in solid rock throughout its entire length. Since the interpretation of “solid rock” is somewhat subjective – due to fractures, formation dips, etc. – it is recommended that, where at all in question, the services of a professional engineer be engaged. This decision is at the discretion of the employer unless ordered by an officer.

Figure 32.6 Protecting workers in excavations