Timber guardrailing for fall prevention

Timber guardrails help prevent falls

Timber guardrailing plays an important role in preventing falls from elevated surfaces. Where it is not reasonably practicable to eliminate the risk of falls, you must reduce the risk so far as reasonably practicable. The hierarchy of control must be followed when controlling the risk of falling more than two metres. The hierarchy of control is the following:

• Level 1 control: work on the ground or a solid construction.
• Level 2 control: use a passive fall prevention device.
• Level 3 control: use a work positioning system.
• Level 4 control: use a fall arrest system.
• Level 5 control: use a fixed or portable ladder (in accordance with regulation 45 of the OHS Regulations) or administrative controls.

Under this hierarchy of control, employers must consider and apply the highest level of control (starting from level 1), so far as is reasonably practicable, before considering the level below it.

Passive fall prevention devices, such as timber guardrailing, are the second highest order of control to reduce the risk of falls. The structure of the timber guardrails is reliant on the correct sizing, material and strength of its components. These components include:

• posts
• handrails and railings
• kick board/toe board and
• connections and fixings.

Information in tables 3 and 4 of the Prevention of falls in housing compliance code is incorrect. The correct information appears in tables 1 and 2 of this guidance. New requirements for full height timber blocking and configuration of railing are also included in figure 2 and 3.

Safety issues

Inadequate timber components used for guardrailing can lead to structural failure when under load whilst acting as fall protection. This may cause falls from heights when under normal use.

Connecting timber posts to the supporting structure should have adequate strength for the intended purpose. Figure 2 gives two connection detail examples.

A suitably qualified person, such as a structural engineer should design and assess the guardrailing and the guardrail supporting structure. It should also be verified to safely resist all loads imposed by the guardrailing system. However, if timber guardrailing meets or exceeds the specifications provided below in this guidance, the design of guardrail fall protection by a structural engineer is not needed.

Specification of timber sizes for guardrailing

When selecting timber for guardrailing, it's essential to ensure the material meets the appropriate quality standards. This means:

• it is free from defects and
• it is the correct size and grade.

Specifications on how to select the correct timber size for handrails and posts, that may form an acceptable passive fall prevention system should;

• Be based on load-bearing capacities required to resist human impact and environmental pressures.
• Be based on durability needs, taking into account the environmental conditions that the timber will be exposed to.
• Incorporate a top rail/handrail between 900mm and 1100mm above the working surface.
• Incorporate a midrail.
• Incorporate a 150mm minimum high toe board if there is a risk of falling objects being dislodged from the walking surface.
• Ensure that the maximum gap between horizontal railings is less than or equal to 450mm.
• Have a minimum stress grade of machine graded pine (MGP) 10 or equivalent, and
• Be inspected by a competent person to ensure there are no knots or other defects that would make the timber unsuitable for use as guardrailing.

Timber sizes for posts and handrails

Note: Tables 1 and 2 are only applicable for guardrails at the perimeter of working platforms, floors and other horizontal surfaces. Seek advice from a structural engineer for specifications for timber guardrailing installed on pitched roofs, parapets etc. or where sheeting/hoarding is installed on the face of the guardrail.

Table 1 - Timber guardrails

*Timber members to be nailed together at maximum 300mm intervals in ‘T’ or ‘L’ sections (refer below).

Note: For options 1 and 2, the flat component on the midrail would have to be cut between posts.

Table 2 - Timber guardrail posts

*Timber members to be nailed laminated in accordance with AS1684.

Installation and maintenance

Timber guardrailing systems need to be inspected regularly. This should help to identify any potential weaknesses or deterioration. Some inspection guidelines may include:

• checks for timber condition,
• structural integrity, and
• attachment stability.

Timber posts, guardrails and fixings that exhibit faults should not be used. Faults include, but are not limited to:

• warped
• twisted
• broken or split
• worn
• notched or surface cut
• corrosion.

Other options:

Sometimes alternative solutions for a passive fall prevention device is required. Scaffolding or proprietary systems may be considered when timber guardrailing does not suffice or in specific scenarios require additional safety measures.

Alternative options that can be adopted for a safe temporary edge protection system include:

• Install a compliant scaffold system up to and around the perimeter of the edge.
• Install a proprietary edge protection system (in accordance with AS 4994.2 or AS 4994.3) that has been designed, manufactured and tested in accordance with AS 4994.1 Part 1: Temporary edge protection – General Requirements.
• Engage a suitably competent person, such as a structural engineer, to provide verification and design sign-off for installations other than those detailed in the above options.

Note: Installation of temporary edge protection systems, including guardrails and scaffolds, need to be installed by a suitably competent person. If a scaffold is installed where there is a risk of a person or object falling more than four metres, an appropriate high-risk work licence must be held by the installer.