Fall arrest systems are installed to keep workers safe when working at height. Common types of fall protection equipment include anchor points, static lines and rigid rails, combined with fall arrest harnesses and lanyards.

Preparing for a fall arrest situation

Fall arrest systems do not stop workers from falling, but are designed to arrest the fall once it has occurred. This means that the worker may fall some distance before the system arrests their fall. The worker will remain safe if the fall arrest system has been designed, installed and used correctly.

When designing and installing fall arrest systems, it is critical to know the correct fall distance clearance, which will ensure that the person using the system does not suffer any injury, potentially resulting from impact with lower level hazards.

What is fall distance clearance?

Fall distance clearance

Fall distance clearance is measured by calculating the total distance that a person falls from the working surface to the position they end up in when their fall has been arrested. It also factors in a clearance distance to account for any stretch in the harness and lanyard.

By correctly calculating this distance, one can ensure that the worker’s fall arrest system will activate so they are not injured by coming into contact with any obstructions below.

How to calculate fall distance clearance?

The fall distance clearance required depends on the following factors:

Elevation of anchorage
Cable deflection, if applicable*
Lanyard length
Lanyard elongation on deceleration pull out (personal energy absorber)
Worker’s height
Fall distance residual clearance (allowance for stretch in the lanyard and harness)

*Line deflection is only added if the operator is attached to a horizontal lifeline to allow for deflection of the cable in the event of a fall, which may increase the fall distance. Check the manufacturer’s guidelines.

Fall Distance Clearance Diagram

(To be used as a guide only.)

Fall distance calculator

In the example above, which shows a distance of 1500mm from the operator's feet to the harness attachment, with a line deflection* of 500mm, a 2000mm excess lanyard length and a 1500mm energy absorber extension, the operator would experience a total fall distance of 5500mm. Into this equation, add the 1000mm residual clearance, which factors in the stretch of both harness and lanyard.

Working on this example, the fall distance clearance is 6500mm.

Some equipment may have different clearance requirements. Please refer to Australian Standard AS/NZS 1891.4 for further information.

*Line deflection is only added if the operator is attached to a horizontal lifeline to allow for deflection of the cable in the event of a fall, which may increase the fall distance. Check the manufacturer’s guidelines.

Fall arrest positioning

Diagram 1

Diagram 1

NOTE: This is to be used as a guide only. Calculations must be based on the conditions and Australian Standards/ Codes of Practice Regulations.

Diagram 2: Measurement of free-fall distance - fixed length lanyard

Extract from AS/NZS 1891.4.2009.8.2

Diagram 2

NOTE: Some configurations may result in a potential free-fall distance in excess of 2.0m (see Clause 8.3 in AS/NZS 1891.4).

System Requirements

Workers must wear a full body harness when connected to any fall arrest system, including a personal energy absorber, compliant with Australian Standard AS/NZS 1891.2:2001 and AS/NZS 1891.4:2009 limiting the force on the anchor and operator to a maximum of 6kN.

Harness connectors must support at least 15kN. Non-compatible connectors may unintentionally disengage (roll-out) so avoid mixing products from different manufacturers. Karabiners supplied with proprietary systems must not be removed or substituted with any other component.

Inspection and Maintenance

Inspection and recertification of fall arrest systems and equipment are required at least every 12 months by a competent person in accordance with manufacturer’s specifications and requirements of Australian Standard AS/NZS 1891.4:2009 Section (9).

Architecture & Design Team

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