Scaffold foundations, platforms, guardrails and access

A scaffold is only as good as what it stands on, what workers stand on and what keeps them from falling off. This lesson covers the foundation (sills, base plates and screw jacks), the platform (planks, decks, spans, overhangs and gaps), guardrails and toe boards, and safe access onto the platform. These are the parts that users see and depend on every day, and they are also the parts most often altered without permission.

Foundations

Every scaffold leg carries load down to the ground. If one leg sinks, slips or punches through, the scaffold can tilt, crack its frames or collapse. A good foundation has three parts:

• Firm ground or structure: compacted soil, concrete, asphalt or a structure that can carry the load. Fill, recently backfilled trenches, frozen ground that will thaw, and ground near excavations need special attention.
• A sill or mudsill: a solid timber plank or engineered pad under the base plates. Sills spread the load over a larger area, bridge small soft spots and keep legs from sinking. Sills usually run continuously under two or more legs.
• A base plate on every leg: centred on the sill and nailed or secured as the manufacturer directs. Screw jacks, if used, sit on base plates and are extended no more than the manufacturer allows.

Ontario requires footings, sills or supports able to carry at least twice the maximum load without settlement or deformation that affects the scaffold, and British Columbia requires bearing plates or sills on a solid surface and limits screw jack extension to two thirds of the jack's length or 60 cm, whichever is less, unless the manufacturer specifies otherwise.

Never use bricks, blocks, pails or scrap lumber to level or support a scaffold. Use screw jacks or adjustable bases and, where the ground slopes significantly, stepped sills or engineered solutions.

Platforms

The platform is the working surface. It must be strong enough, wide enough, fully decked and secured so that boards cannot slide, tip or lift.

• Fully planked or decked: no large gaps between boards or between the platform and the uprights. Ontario and other provinces require platforms to be at least about 460 mm wide, and British Columbia at least 50 cm (30 cm for ladder jack and pump jack systems).
• Close to the work: platforms should be as close to the work face as practicable; where the gap is large, a guardrail is needed on the work side too.
• Planks secured and with the right overhang: Ontario requires planks to extend at least 150 mm and not more than 300 mm beyond their supports, and to be secured so they cannot slide off. Too little overhang lets a plank slip off its support; too much creates a trap end that tips when someone stands on it.
• Overlapping planks: where planks overlap, they should overlap over a support and be secured, and the overlap should be enough that neither plank can slip off.
• Rated for the load: planks must be scaffold-grade lumber, laminated veneer lumber or manufactured decks, marked or certified for the span and load. Ordinary construction lumber is not scaffold plank.
• In good condition: no splits, large knots, rot, saw cuts, notches, burns or warping; metal decks without cracked welds or bent hooks.
• Clear: free of debris, ice, snow, mud and tripping hazards; materials stacked neatly and within the rated load.

Plank spans

Solid sawn scaffold planks have maximum spans that depend on the duty class. Manufacturers and CSA S269.2 tables give the values; as a guide, the heavier the duty class, the shorter the allowed span, so a span that is fine for painters may be too long for masons with stockpiled block. Manufactured decks and laminated veneer lumber planks have their own published spans.

Guardrails and toe boards

Guardrails are the primary fall protection on scaffolds. A complete guardrail system has a top rail, a midrail or equivalent such as screens or mesh, and a toe board.

• Ontario's construction regulation requires a guardrail with a top rail 0.9 m to 1.1 m above the platform, an intermediate rail and a toe board, on open sides and ends of platforms where a worker could fall 3 m or more, or less if the hazard is unusual, such as falling into machinery or water.
• Guardrails must withstand the specified loads, which in Ontario are set in the guardrail sections of the regulation.
• Toe boards stop tools and materials from falling off the platform edge and protect people below. Many provinces require toe boards at least about 89 mm high where people work or pass below.
• Cross braces on frame scaffolds can sometimes serve as a top rail or midrail if they cross at the right height, but only where the regulation allows it and the competent person confirms it.
• Guardrails must not be removed to pass materials or to work, unless other fall protection is in place and the guardrail is replaced immediately afterwards.

Access onto the scaffold

Climbing the outside of a scaffold frame, cross braces or end frames not designed as ladders is one of the most common causes of scaffold falls. Every working platform needs safe access.

• Use an attached ladder, a built-in ladder frame designed for climbing, a stair tower or direct access from the building. Ontario and Alberta set rules for vertical ladders on scaffolds, and British Columbia requires safe access to every platform.
• Ladders on scaffolds must be secured, extend about 1 m above the platform or have grab rails, and land on the platform without leaving a gap.
• Access openings in guardrails need a gate or a safety chain that closes behind the user, or a ladder that lands inside the guarded area.
• Stair towers are best for frequent access, carrying tools and large crews.

Bracket, pump jack and ladder jack scaffolds

Light scaffolds used in residential and small commercial work have their own limits. Bracket scaffolds hang from wall brackets nailed or bolted to the structure; the brackets must be rated for the load and fastened as the manufacturer directs, and the platform must still have guardrails where the fall height requires them. Pump jack scaffolds use vertical poles, often wood or aluminium, braced to the wall, with jacks that climb the poles; pole height, bracing and load are limited, and guardrails or fall protection are needed. Ladder jack scaffolds support a plank between brackets hooked onto two ladders; they are limited to light work at low heights, the ladders must be suitable, and only a limited number of workers may use them at once.

Provincial regulations set specific limits for these types, for example British Columbia permits a narrower platform of 30 cm with ladder jack and pump jack systems, and Alberta's OHS Code has sections on bracket, ladderjack and roofing bracket scaffolds.

Housekeeping on platforms

Platforms fill up quickly with offcuts, packaging, mortar droppings and tools. Clutter causes trips at the edge and overloads planks. Keep only the materials needed for the next few hours on the platform, stack them neatly away from guardrails and access points, clean up at the end of each shift, and use chutes or bins to remove debris rather than throwing it over the edge.

Working near the platform edge

Even with guardrails, avoid standing on materials or buckets to gain height, because that raises the worker above the top rail and defeats it. If more height is needed, the competent person should add a lift. Never sit or lean on guardrails, and never use them to support planks, ladders or materials.

Users can help keep platforms safe by reporting any missing plank, guardrail or toe board as soon as they see it, and by never working on a platform that is not complete.