OHS Code Explanation Guide

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

Section 457 Alternative to temporary protective structure

Subsection 457(1)

Instead of complying with section 456, this section permits an employer to use shoring, stringers and bracing constructed of lumber (see Figure 32.14) that complies with Schedule 9, or alternate materials, in trenches 1.5 metres to 6 metres deep. If alternate materials are used, they must possess equal or greater properties than those of lumber. For ease of reference, Schedule 9 is shown as Table 32.2.

Figure 32.14 Trench protected by shoring

Table 32.2 Shoring component used in excavations, trenches, tunnels and underground shafts (appears in the OHS Code as Schedule 9)

Exterior grade plywood can be installed as a substitute for 38 millimetres shoring elements if the plywood meets the requirements of either of the two referenced CSA Standards.

Subsection 457(2)

Mechanical devices such as screw jacks and hydraulic equipment can be used in place of the shoring, stringers or bracing described in Schedule 9. The devices must be at least equivalent in strength and reliability to the shoring, stringers or bracing.

Schedule 9

Subsection 457(3)

The use of stringers in trenches less than 2.4 metres deep in “hard and compact soil” is optional.

Subsection 457(4) and 457(5)

Where there is a risk of additional stress, vibration or weight being placed on the walls of a trench (see Figure 32.3), additional protection certified by a professional engineer must be used. In assessing the risk to workers, the employer must consider any of the following being placed, passing by, or working within a distance equal to the depth of the trench:
(a) vehicular traffic;
(b) machinery, which may include road compaction equipment or compaction equipment used during backfill activities close to the excavation; and
(c) heavy object(s).

Additional protection is also required to compensate for the stress, vibration or weight resulting from the trench being adjacent to, or abutting, a building or other structure.