OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 23 Scaffolds and Temporary Work Platforms

Section 323 CSA Standard applies

CSA Standard CAN/CSA-S269.2-M87 (R2003), Access Scaffolding for Construction Purposes, provides rules and requirements for the design, fabrication, erection, inspection, testing, maintenance and use of scaffolding equipment, materials and equipment where scaffolds are erected to provide working platforms for workers and materials during the construction, alteration, repair or demolition of buildings and other structures. The Standard does not apply to

(a) suspended scaffolds or swing stages,
(b) truck or vehicle mounted platforms,
(c) falsework,
(d) shoring, or
(e) self-elevating work platforms.

The following is a selection of requirements within the Standard. Users of the OHS Code must comply with these requirements and all others in the Standard.

Used Lumber
Where lumber has been mechanically damaged (including repeated nailing of the same piece of lumber to the point that its mechanical integrity is questionable) or has deteriorated due to insects, decay, or chemical attack, the lumber must not be used unless a qualified lumber grader regrades it. (Clause 4.3)

Loads on Guardrails, Midrails and Stair Handrails
Rails must be capable of resisting, without failure, a single point load of not less than 900 newtons (202 pounds-force) applied in any direction on any span. (Clause 5.5.1)

Posts must be capable of supporting, without failure, a single point load of not less than 900 newtons (202 pounds-force) applied in any direction at the level of the top rail. (Clause 5.5.2)

General Stability of Scaffolding
The ratio of maximum height to minimum horizontal width of an access scaffold must not exceed 3:1, unless lateral support is provided as required below. (Clause 6.6.2)

External Lateral Supports
External lateral supports must be installed at vertical intervals, not exceeding 3 times the minimum width of the structure, and at every third bay of scaffolding longitudinally. (Clause 6.6.3)

External lateral supports must consist of
(a) a rigid connection to another structure or building, or
(b) guy wires or other supplementary devices securely fastened to adequate anchors.

External lateral supports must be installed at vertical intervals not exceeding every third tier and every third bay of scaffolding longitudinally, or 6.4 metres (21 feet), whichever is less. (Clause 6.6.3.1)

Sills
A sill is a wood, concrete or metal footing used to distribute the load from a standard or vertical post or base plate to the ground. Sills must be sound, rigid and capable of adequately supporting the maximum load to which the scaffold is likely to be subjected. Any settling or deformation of the sill should not affect the stability of the scaffold. (Clause 6.6.8.2)

To ensure proper distribution, sills must be continuous at least under two consecutive vertical legs or vertical supporting members as shown in Figure 23.1. (Clause 6.6.8.3)

Figure 23.1 Mudsill layout

Areas Requiring Special Attention in Foundation Design
Special consideration needs to be given to the following conditions:
(a) In the absence of soil tests and a detailed design, topsoil or other unsuitable material must be excavated to obtain an adequate bearing capacity of not less than 75 kilonewtons per square metre (1566 pounds/square foot). Topsoil or other unsuitable material must be excavated if necessary to obtain adequate bearing capacity.
(b) When frozen ground is used as a foundation for all or part of the sills, thawing must be prevented.
(c) Sills in areas where variable degrees of foundation compaction and bearing capacity exists, as in previously excavated ground, trenches, and backfilled areas, must be designed to span soft areas, or other appropriate measures must be taken to limit differential settlement to acceptable levels.
(d) Sills in areas subject to erosion, such as the edges of slopes and terraces, must be protected.
(e) Reduction of bearing capacity of the foundation due to changes in ground water elevation during construction or due to groundwater flows must be prevented.
(f) Sills resting on thin concrete slabs, pan or waffle slabs, and slabs containing voids must be designed and located so as to safely distribute the concentrated loads.
(g) Where the required foundation bearing capacity cannot be safely developed by other means, access scaffolding must be supported on piles providing the required load capacity.
(Clause 6.6.8.6)

Leg Adjustments
Adjustment devices must be provided at the base of all uprights of frames where foundation settlement is uncertain or the support surface is uneven, sloping or stepped. Travel of adjustment devices must be mechanically limited to the maximum travel specified in the manufacturer’s specifications. If extension of the device reduces allowable load, such information must also be specified in the manufacturer’s specifications and established by test. (Clause 6.7.7)

Supervision and Erection Procedures
Only competent persons experienced in the erection of access scaffolding are allowed to supervise assembly of the scaffold. This ensures that the erection is carried out according to acceptable practices, such that
(a) the requirements of the drawings or suppliers’ literature are strictly complied with,
(b) no unusual settlement of foundations or strains in other external supports occur, and
(c) the correct components and materials are being used.
(Clause 7.2.1.1)

Sills and Foundations
When foundations for access scaffolding are located in areas where the soil bearing capacity is, or is likely to become, inadequate to support the loads without detrimental settlement,
(a) the soil beneath sills must be stabilized with cement to an adequate depth,
(b) soil beneath sills must be removed and replaced with concrete having a low cement content,
(c) sills must be founded on a layer of compacted gravel 150 to 300 millimetres thick, or
(d) piles must be driven into the soil beneath the scaffolding supports to provide adequate load-carrying capacity.
(Clause 7.2.4.2)