Prusik slings: Understanding the hazards
June 13, 2018 - Workers using personal fall protection systems sometimes instinctively grasp their systems’ rope grabs during falls. Some commercially available rope grabs are manufactured with “anti-panic” features that enable the rope grabs to work properly by locking onto the lifeline even when they are grasped. Some workers use Prusik slings as rope grabs. A Prusik sling, however, does not have an anti-panic feature. Therefore, grasping a sling’s Prusik knot can prevent the knot from tightening around the lifeline, allowing the worker to fall.
This bulletin explains the hazards of using Prusik slings as rope grabs, and discusses why it’s safer in most cases for workers to use rope grabs that meet CSA or ANSI standards and include anti-panic features.
What is a Prusik sling?
A Prusik sling is a length of rope with its ends secured together to create an “endless loop.” When used as part of a fall protection system, the Prusik sling is attached to a thicker lifeline by tying the sling into a Prusik knot (see illustration). You can freely slide a Prusik knot along the lifeline by hand, but it should tighten around the lifeline when the sling is pulled by its loop.
In recreational rope systems, Prusik slings are used for various purposes, including lifeline ascent, fall arrest, and rescue.
In the workplace, a Prusik sling can be used in place of a rope grab in a fall protection system in some circumstances. However, a Prusik sling has significant limitations. Prusik slings may only be used when the worker:
• Is trained and proficient in creating a Prusik sling that is safe and appropriate for the fall protection system
• Understands the Prusik sling’s functions and limitations
Hazards of using Prusik slings in fall protection systems
In order for a Prusik sling to restrain a worker or arrest a fall, the Prusik knot must tighten around the lifeline. Various factors may prevent a Prusik knot from tightening:
“Death grip” — A falling worker may instinctively grasp the Prusik knot with a very strong, tight hold that prevents the knot from tightening, which prevents the sling from arresting the worker’s fall. For this reason, a Prusik sling may be better suited for a travel restraint system than a fall arrest system.
Loose knots — A knot that is too loose, improperly dressed, or inadequately tied may slide freely along the lifeline without tightening.
Icy ropes and debris — Ice or frost may allow the knot to slide freely along the lifeline without tightening. Keep the knot free from ice and from debris such as leaves, twigs, or soil that may prevent it from working properly.
A Prusik sling that has arrested a fall may be damaged from shock-loading, melting, and burning. A fall protection system that has arrested a worker’s fall must be removed from service until it has been inspected and recertified as safe for use by the manufacturer or its authorized agent, or by a professional engineer.
Safe work practices
• When using a rope grab in a personal fall protection system, use one made to an applicable CSA and/or ANSI standard and equipped with an anti-panic feature.
• Use Prusik slings as rope grabs only in rare cases where the nature of the work being done makes them the safest practicable option.
• Properly tie, dress, and set all knots.
• Keep Prusik slings free from ice and debris.
• Follow the detailed instructions found in Guideline G11.5-4, Equipment standards — Prusik sling/Triple sliding hitch.
For requirements related to the use of Prusik slings as part of a personal fall protection system, see the following section of the Occupational Health and Safety Regulation and the related guideline (available at worksafebc.com):
• Section 11.5, Equipment standards
• Guideline G11.5-4, Equipment standards — Prusik sling/Triple sliding hitch
The following resources are also available on worksafebc.com:
• An Introduction to Personal Fall Protection EquipmentEquipment
• Toolbox meeting guide: Rope grabs
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