What Is the 1/10 Rule for Retiring a Flat Sling?

A rigging supervisor inspects a flat sling that has been in service for several months. The edges are slightly frayed, and the surface shows some abrasion. The sling looks like it has seen better days—but is it still safe to use?

 

The answer lies in a simple rule: the 1/10 rule. According to EN 1492-1, the European standard for flat woven webbing slings, when abrasive wear reduces the webbing width by one-tenth or more of the original width, the sling must be removed from service immediately . ASME B30.9 similarly recognizes excessive abrasive wear—wear that reduces the sling's cross-section or exposes core yarns—as a condition requiring retirement.

 

Lishenflex has been manufacturing synthetic flat slings for over two decades, and our field data show that abrasion is one of the most common causes of sling retirement. Yet many riggers struggle to determine when wear is "excessive." The 1/10 rule provides a clear, measurable threshold.

 

What Is the 1/10 Rule?

The 1/10 rule states that a flat sling must be removed from service when abrasive wear has reduced the webbing width by 1/10 or more of the original width.

 

In practice, this means:

 

Source: EN 1492-1; ASME B30.9

 

The rule applies to abrasive wear specifically—not cuts, tears, or other damage types. However, if the 1/10 threshold is reached through a combination of wear and other damage, the sling must still be retired.

 

Why the 1/10 Rule?

The 1/10 threshold is not arbitrary. According to industry testing data, a 10% edge cut can reduce a sling's capacity by 35% . While the 1/10 rule primarily addresses abrasive wear (rather than cuts), the principle is the same: once the webbing width is reduced by 10%, the sling's strength is compromised significantly.

 

The EN 1492-1 standard specifies that flat woven webbing slings must be inspected for abrasive wear that damages the webbing to the point where the original width is reduced. ASME B30.9 similarly requires that slings with excessive abrasive wear be removed from service.

 

Lishenflex's lab testing confirms that slings with 10% width reduction due to abrasion show a measurable decrease in breaking strength—typically 15–25% depending on the wear pattern. This is why the 1/10 rule is a critical safety threshold.

 

How to Measure Webbing Width

Accurate measurement is essential for applying the 1/10 rule correctly.

 

Equipment Required

 

• Measuring tape or ruler with millimeter graduations

• Calipers for more precise measurements (recommended for borderline cases)

• Magnifying glass (optional) for inspecting edge wear

 

Measurement Procedure

 

1. Select the most worn section of the sling—typically at the midpoint of the sling length or at points of contact with the load or lifting hardware

 

2. Measure the original width—refer to the sling's identification tag or manufacturer specifications. If the original width is not available, measure an unworn section of the same sling

 

3. Measure the worn width—at the narrowest point of the wear area

 

4. Calculate the wear = Original width − Worn width

 

5. Calculate the percentage = Wear ÷ Original width × 100%

 

6. Apply the 1/10 rule—if wear ≥ 10% of original width, retire the sling

Key Points

 

• Measure across the entire width—not just at the deepest point

• Measure at multiple points—wear may be uneven

• Document your measurements—maintain inspection records per ASME B30.9 requirements

 

Common Misunderstandings

Several common misconceptions can lead to incorrect application of the 1/10 rule:

 

According to ASME B30.9, excessive abrasive wear is defined as wear that exposes the core yarns or reduces the sling's cross-section. While ASME B30.9 does not explicitly state "1/10" in the same way EN 1492-1 does, the standard recognizes that once wear reaches the point where the core is exposed or the cross-section is reduced, the sling must be retired.

 

EN 1492-1, however, is explicit: abrasive wear reducing the webbing width by 1/10 or more is a condition for immediate removal from service.

Other Retirement Criteria for Flat Slings

The 1/10 rule is one of several retirement criteria. According to ASME B30.9, flat slings must also be retired when:

 

• Missing or illegible identification tag

• Acid or caustic burns

• Evidence of heat damage—melting, charring, or blistering

• Holes or tears that expose core yarns

• Broken or worn stitching in load-bearing splices

• Knots in the sling body

• Discoloration and brittle or stiff areas indicating chemical or UV/sunlight damage

• Fittings that are pitted, corroded, cracked, bent, twisted, or broken

 

Per EN 1492-1, flat slings must also be retired when there is cutting damage that penetrates the webbing or seam damage affecting the load-bearing capacity.

 

Practical Application

To ensure the 1/10 rule is applied consistently:

 

1. Train your team—ensure all riggers and supervisors know how to measure webbing width accurately

 

2. Use calipers for precise measurement—tape measures can be inaccurate for small variations

 

3. Document inspections—maintain records showing original width and measurement dates

 

4. Mark questionable slings—clearly identify slings that are borderline for closer inspection

 

5. Retire immediately—when wear reaches 10%, remove the sling from service and destroy it

 

Summary and Practical Recommendations

The 1/10 rule provides a clear, measurable threshold for retiring flat slings due to abrasive wear. Once the webbing width has been reduced by 10% or more of the original width, the sling's strength is compromised and it must be removed from service.

 

Key takeaways:

 

1. Measure webbing width accurately—use calipers for precise measurement

 

2. Apply the 1/10 rule—wear ≥ 10% of original width = immediate retirement

 

3. Combine with other inspection criteria—the 1/10 rule addresses abrasion, but other damage types also require retirement

 

4. Document inspection results—maintain records per ASME B30.9 requirements

 

5. Train your team—ensure everyone can apply the rule correctly

 

Lishenflex manufactures polyester flat slings to EN 1492-1 and ASME B30.9 standards, with clear color-coded capacity markings and inspection guidance. We provide measurement tools and training to help your team apply the 1/10 rule effectively.

 

If you need assistance establishing a sling inspection program—or need help determining whether your current slings have reached the 1/10 retirement threshold—please send an email to sales@lishenflex.com, and our technical team will provide one-on-one support.