Safer scaffolding – wrap it up!

Where work is carried out close to pedestrian or vehicle access, it’s a good idea to use scaffolds that are fully screened to minimise the risk to the public from falling objects. As long as toe boards are tightly fitted to screened scaffolds, all substances should be contained.

Risks of screened or contained scaffolding

Scaffolds fitted with screening are heavier due to increased environmental loads (such as wind loads or rain loads). This increases the dead load of the scaffold, and the risk of it being blown over.

To avoid this happening, you should consider the following factors when selecting screening material:

• What is the wind loading?

• What degree of protection is required?

• Is containment of dust a requirement?

• What chemicals will be used from the scaffold?

• What are the ventilation requirements?

• How flammable is the screening?

• For ventilation purposes, how porous is the screening material?

• How much light is needed?

• What are the size of sheets or screen sections?

• What are the requirements for fixing the screening?

Different requirements for each of these factors will determine what type of screening material should be selected.

What is ‘Dead Load’

The dead load is the total weight of all the structural components and equipment that form the scaffld. It is generally a static load.

Design requirements

Sheeted scaffolds must be designed by a chartered professional engineer, unless there is sufficient information available using the manufacturer’s specifications and calculated or known loads.

Information on environmental loadings can be found in AS/NZS1576.1: Scaffolding – General requirements and AS/NZS1170.0: Structural Design Actions – General Principles.

Different requirements will determine what type of screening material should be selected

The design of a screened scaffold should consider:

• The weight of the screening.

• The environmental load on the scaffold and the supporting structure.

• The position of the screened scaffold in relation to other structures.

• The fixing in respect to the strength of the screening.

• The ability of the fixing to fail.

• The structure’s ability to support any imposed loads.

Increased stability may be achieved by increasing the number or strength of ties or by using plan and dogleg bracing, buttresses or counterweights.

Fixing must have a fail capacity to prevent the structure being damaged, if forces (especially wind) are beyond the ability of the ties or screening to withstand such forces.

Installation

When installing screening:

• Fix it to fully decked and guard-railed platforms.

• Fit to the outside of the scaffold (unless specified otherwise).

• Flush the outside of the scaffold to prevent tubes or other items from protruding.

• Make it continuous, either by using sufficient overlap (preferable) or by carefully butt-joining the screening.

• Secure the top edge of the screening before fixing the bottom edge.

• Use a tag line in windy conditions to control the screening during fixing.

• Keep the screening taut.

• Lap under from the top for containment and lap over from the top for protection.

• Keep the ends of the scaffold as close as practical to the building or structure to prevent the wind getting behind the screening.

When using proprietary scaffolding that does not have a positive joint between the vertical standards in conjunction with screening, it is recommended that joints be spliced or that additional bracing be provided across the joins to prevent uplift of the join.

Proprietary systems with additional scaffolding components that are not covered by the manufacturer’s specifications should be classified as special duty scaffolds. All special duty scaffolds must be notified to Ministry of Business, Innovation and Employment (MBIE).

For more information on notification, visit www.business.govt.nz/worksafe/ 

Proprietary system

Propriety scaffold systems have been designed by a chartered professional engineer, as reflected in the manufacturer’s specifications for the design and use of the equipment.

Where work is carried out close to pedestrian or vehicle access, it’s a good idea to use scaffolds that are fully screened to minimise the risk to the public from falling objects

Contained scaffolds

While there are different varieties of shade cloth, wind must be able to pass through it depending on the screening’s porosity. This reduces the wind loading on the scaffold and structure while providing ventilation and light.

Note: Hessian must not be used as screening as it is not fire retardant.

Common materials used for screening or containment:

• Shade cloth.

• Shrink wrap.

• Sealed panel systems.

• Monaflex.

• Plastic.

• Keder sheeting.

Products such as Monaflex, shrink wrap, keder sheeting and sealed panel systems are good for creating a strong scaffold that can contain harmful substances such as asbestos. However, these products greatly increase the loading and pressure on the scaffold and supporting structures.

Consideration must be given to relieving this pressure in emergency situations. Also, given their nature, using these products for screening or containment can create poor ventilation and other hazards associated with confined spaces, so make sure users are adequately trained and wearing proper safety gear.

Contained scaffolds should be notified to MBIE as special duty scaffolds.

Standards

• Structural Design Actions – General Principles. AS/NZS1170.0
• Scaffolding – General requirements AS/NZS1576.1

Further references

• Best Practice Guidelines for Working at Height in New Zealand
• Best Practice Guidelines for Working on Roofs
• Best Practice Guidelines for Scaffolding in New Zealand

These references are available from www.dol.govt.nz