Perimeter screens on construction sites

Information about preventing perimeter screen connections from failing.

Shape

Perimeter screen connection failures

Perimeter screens are large steel structures that can weigh up to several tonnes each. If a screen falls inward (into a site) or outwards of a site (eg into a neighbouring property, onto public roads), it can have catastrophic consequences causing serious injuries and loss of life.

Examples of incidents where perimeter screen connection points have failed include:

  • a threaded bar used to fix screen needle components failed and the screen fell backwards into the site
  • a threaded bar that was installed in a cast-in anchor came loose and the perimeter screen fell back into the site
  • a threaded bar pulled out of a cast-in anchor as the screen was being jumped
An incident in which perimeter screens fell backwards into a construction site
An incident in which perimeter screens fell backwards into a construction site

Safety risks

Due to the significant risks associated with perimeter screens, the support points should be treated as critical structural connections.

The following factors increase the risk of perimeter screen connection points failing:

  • Inadequate supplier information or specifications about how to install and secure the screens correctly.
  • Lack of redundancy in the design of perimeter screen connections, for example, where the failure of a single fixing can result in the collapse of the screen.
  • Failure to install the fixings that connect the perimeter screen to the supporting structure in accordance with the supplier’s instructions.
  • Fixings are not torqued in accordance with manufacturer's specifications and instructions to ensure they do not come loose under fluctuating stresses and strains from wind (eg cyclic wind loads).
  • Incorrectly installed coarse threaded fixings are more likely to come loose under cyclic loads (eg wind).
  • Using incompatible or incorrect strength or grade components (eg fixings, threaded bars).
  • Re-using worn components, for example threaded bars (z-ties) that no longer engage properly.
  • Lack of regular inspections/testing to confirm that fixings remain secure and conform to the recommendations of the manufacturer/supplier and applicable Australian Standard (see AS/NZS 4994.4:2018 Temporary Edge Protection: Perimeter Protection Screens).

Legal duties

Under the Occupational Health and Safety Act 2004 specific legal duties apply to persons involved in work requiring the use of perimeter screens, including:

  • Employers must, so far as is reasonably practicable, provide and maintain a working environment for their employees that is safe and without risks to health.
  • Employers must ensure, so far as is reasonably practicable, that persons other than employees are not exposed to risks to their health or safety arising from the conduct of the undertaking of the employer.
  • Persons who install, erect or commission plant (eg perimeter screens) at a workplace must ensure, so far as reasonably practicable, that nothing about the way in which it is installed, erected or commissioned makes its use unsafe or a risk to health.

For guidance on the duties relating to designers, manufactures and suppliers of plant please refer to WorkSafe's Compliance code: Plant.

Under the Occupational Health and Safety Regulations 2017, additional duties may apply, particularly where high risk construction work (HRCW) is being undertaken, including:

  • Employers must ensure HRCW is not performed if there is a risk to health or safety unless a safe work method statement (SWMS) is prepared and followed. See 'High risk construction work' section below.
  • The SWMS must identify hazards and risks associated with the task and describe how they will be controlled.
  • Employers must review and, if necessary, revise SWMS whenever the HRCW changes or where there is an indication that the control measures are not controlling the risks adequately, including after an incident that has occurred during HRCW.
  • Persons performing perimeter screen work (installation, alterations, jumping or dismantling) must hold a high risk work licence (HRWL) with the appropriate HRWL class, at a minimum, a basic rigging licence.
  • Employers have specific duties to prevent involuntary falls of more than 2 metres at a workplace. These include an employer's duty to, so far as is reasonably practicable, identify any task that involves a fall hazard and control any risk associated with a fall in accordance with the hierarchy of control.

For guidance on the prevention of falls, hierarchy of control and other duties that apply refer to WorkSafe's Compliance code: Prevention of falls in general construction.

Recommended measures to control risks

Perimeter screens should be appropriately designed, installed, inspected and maintained to ensure they do not fail.

The following measures should be implemented to control the risks associated with perimeter screen connections.

Design and planning

  • Seek detailed specifications and installation instructions from suppliers or engineers, including detailed component specifications, detailed tightening or tensioning methods, inspection requirements, and acceptance and rejection criteria for reusable components.
  • Ensure a detailed engineering design has been produced for the perimeter screen in accordance with relevant Australian Standards (AS/NZS 4994.4); where necessary the design may need to be site-specific, taking into account the buildings’ profile and potential wind loadings as the buildings’ height increases (see Further information).
  • Ensure the engineering design provides sufficient redundancy that failure of a single fixing or connection point will not result in a catastrophic failure (see Recommended perimeter screen connection configurations - figures 4, 5 and 6).
  • Employers (including principal contractors, subcontractors and builders) need to consider the sequencing and timing of screen jumping and form work to ensure sufficient time is available for safe installation, jumping and/or removal.

Installation and jumping

  • Use only specified components.
  • Ensure all components are compatible prior to installation (in particular check the engagement of threaded bars in cast-in anchors).
  • Ensure perimeter screen components are easily identified and not confused with other components on-site (eg with formwork components).
    • Consider painting perimeter screen components a distinctive colour and storing separately.
Components used in perimeter screens and formwork may appear similar, however critical differences can mean they are not safely interchangeable. The correct diameter, thread pitch, bar shape and strength/grade are required to align with the engineering specification.
Components used in perimeter screens and formwork may appear similar, however critical differences can mean they are not safely interchangeable. The correct diameter, thread pitch, bar shape and strength/grade are required to align with the engineering sp
  • Inspect components for wear prior to installation and discard excessively worn components or those that do not meet the manufacturer's acceptable wear specifications.
  • Structurally critical perimeter screen components and welds (on needles, screens, prop connections, lifting points etc.) should be non-destructively tested in accordance with the recommendations of the designer or engineering specification.
  • Ensure any fixings that are used in low strength concrete are tested specifically for that application and carefully review engineering claims that cannot be supported by verified testing results.

For further guidance refer to WorkSafe's guidance Erection of concrete panels on early age low strength concrete.

  • Confirm concrete slabs have achieved sufficient strength prior to erecting or jumping screens by keeping concrete test cylinders on-site in the same conditions as the slab or use of electronic probes (refer to WorkSafe Guidance above for information relating to risks associated with connecting to low strength concrete).
    • Evidence of concrete test results should be readily accessible on site.
  • Install the perimeter screen, connecting elements (needles and braces) and fixings in accordance with the supplier's instructions.
  • Ensure all persons involved in the installation of the perimeter screens (including crane crews) are trained in the correct procedures for installation, jumping and dismantling  and confirm their competency prior to commencing installation.
  • Ensure that personnel who are responsible for supervising the perimeter screen works are trained in, and understand, the supplier's instructions and engineered design.
  • After initial installation, a competent person (eg an engineer familiar with the perimeter screen system) should provide a sign off confirming that the screen has been installed as per the supplier's instructions and engineered design.
  • Screen crew should complete a pre and post-jump checklist.
  • Fasteners that require a specific installation torque need to be tightened using a calibrated torque wrench and not a rattle gun; this can lead to over or under tightening/torqueing.

High risk construction work

The task of installing, altering, jumping and dismantling the perimeter screens is generally considered to be HRCW. A SWMS must be prepared before commencing any HRCW.

Note: where there is a risk of a person falling more than 2 metres, this is HRCW.

The system of work in relation to installing, jumping, maintaining and dismantling the perimeter screens needs to be documented in the SWMS. The system of work should be developed:

  • following the manufacturer or engineer's specification requirements
  • detailing the correct tightening or tensioning procedure for the fixings
  • with the manufacturer/engineer’s specifications attached to the SWMS (and available on-site)

The perimeter screen works must then be completed in accordance with the SWMS.

Inspection and maintenance of fixings

Ensure a competent person inspects and confirms all the fixings:

  • are correctly tightened prior to releasing the screen from the crane or jacking device
  • remain snug and tight and these inspections are documented as part of the safe system of work

Fixings that require a specific torque should be:

  • visually inspected daily
  • physically tested weekly and after adverse weather events (including high winds) using a calibrated torque wrench to confirm fixings are secure

These inspections and tests should be documented and records should be kept as part of the safe system of work.

Recommended perimeter screen connection configurations

Typical tower setup

Using minimum two (2) levels of support brackets.

Typical tower setup - maintain support at two levels simultaneously to reduce the risk of collapse.
Typical tower setup - maintain support at two levels simultaneously to reduce the risk of collapse.

Podium Initial Setup - Option 1

Support should be maintained at two levels simultaneously, so far as is reasonably practicable, to reduce the risk of collapse.

Podium initial setup - option 1 demonstrates a screen dropped one (1) level down from the supporting bracket and an additional connection installed at lower slab level.

Note: Screen props must be installed at the nominated minimum propping heights on received drawings and propping angles must be within 45-60°range from horizontal.

Podium initial setup, option 1
Podium initial setup, option 1

Podium Initial Setup - Option 2

Support should be maintained at two levels simultaneously, so far as is reasonably practicable, to reduce the risk of collapse. Podium initial setup - option 2 demonstrates a scenario where only a single slab has been constructed. As such, connection is only possible at one level. This setup requires full engineering confirmation for use.

Site location and wind loads will determine acceptability of this approach. Consider using shorter screens to reduce reaction loads on connections (push-pull props and mechanical fixings).

Note: Screen props must be installed at the nominated minimum propping heights on received drawings and propping angles must be within 45-60°range from horizontal.

Podium initial setup, option 2
Podium initial setup, option 2

More information