Flat Sling Inspection Guide: How to Spot Cuts, Snags, and Stitching Failure

A rigging supervisor grabs a flat sling from the storage rack. A quick glance shows no obvious problems. The sling goes onto the crane hook. The load lifts—and then drops. The investigation reveals the cause: a cut in the webbing that exposed the load-bearing core, invisible from the angle where the supervisor stood.

This scenario is preventable. According to ASME B30.9-2021, synthetic webbing slings must be inspected before each use, and any sling that appears to be damaged shall not be used unless inspected and accepted as usable . OSHA enforces these requirements through 29 CFR 1910.184(i)(9), and employers who fail to remove damaged slings from service face serious citations and penalties .

Lishenflex has been manufacturing synthetic flat slings for decades, and our field experience shows that many rigging failures occur in slings that showed warning signs someone overlooked or misjudged. This guide breaks down the three most common damage categories—cuts, snags, and stitching failure—and explains exactly when each requires retirement.

1. Cuts and Tears: When Surface Damage Becomes Critical

Cuts and tears are among the most visible damage types, but not every cut requires immediate retirement. The key question: does the damage expose the load-bearing fibers?

1.1 What ASME B30.9 and OSHA Require

Per ASME B30.9-2021, Section 9-5.9.5(d), a synthetic webbing sling shall be removed from service when holes, tears, cuts, or snags are present . OSHA 29 CFR 1910.184(i)(9)(iii) uses identical language, listing snags, punctures, tears or cuts as conditions requiring immediate removal .

The Canadian Centre for Occupational Health and Safety (CCOHS) confirms that holes, tears, cuts, and snags are among the visible damage types that make a synthetic web sling unusable . The Workforce Safety guide adds that synthetic web slings with snags, punctures, tears or cuts must be discarded—they cannot be repaired .

1.2 Distinguishing Critical Cuts from Superficial Damage

Not all surface irregularities are equal. The distinction lies in depth and fiber exposure:

• Superficial surface cut —only the outermost fibers are affected; no core exposure. Monitor closely.

• Deep cut exposing core —the protective webbing layer is penetrated, and load-bearing fibers are visible. Immediate retirement.

• Edge cut —damage that reduces the effective width of the webbing. Immediate retirement, even if the cut appears small.

The Maine Department of Labor guidance explains that broken fibers of equal length indicate the sling has been cut by an edge—and this requires removal from service. The guide emphasizes that red core warning yarns may or may not be visible, and their absence does not mean the sling is safe .

Lishenflex's lab testing confirms that even a 10% edge cut can reduce sling capacity by 35%—far more than most riggers would estimate. This is why ASME B30.9 treats any cut that compromises the webbing structure as a retirement condition.

1.3 Real-World Consequence

OSHA enforcement data demonstrates the real cost of ignoring cuts. In Advanced American Construction, Inc., employees were observed using synthetic web slings with visible tears and punctures along the body during lifting operations—resulting in a violation citation . In B & K Concrete and Construction, Inc., synthetic web slings used for steel erection had snags, punctures, tears, cuts, and broken/worn stitches that were not immediately removed from service .

2. Snags and Punctures: Hidden Fiber Damage

Snags and punctures differ from cuts in one critical way: they often pull fibers rather than sever them, creating damage that is less visible but equally dangerous.

2.1 What Constitutes a Snag or Puncture

A snag occurs when the webbing catches on a protrusion, pulling fibers out of the weave. A puncture is a hole created by a sharp object penetrating the webbing. Both are listed in ASME B30.9-2021, Section 9-5.9.5(d) as conditions requiring immediate removal from service .

The Maine Department of Labor inspection guide describes snags as areas where fibers stand out from the rest of the sling surface—punctures or areas where fibers protrude . The guide warns to avoid sling contact with protrusions, both during lifts and while transporting or storing.

2.2 Why Snags Are Dangerous

A snag may not sever fibers immediately, but it disrupts the weave structure that distributes load evenly. Under subsequent loading, stress concentrates on the remaining intact fibers, accelerating failure. CERTEX Denmark specifically warns that local abrasion, as distinct from general wear, can be caused by sharp edges and can lead to the cover becoming cut and/or serious loss in strength .

Workforce Safety lists snags alongside cuts and punctures as conditions requiring discarding . The Northwest Territories Workers’ Safety and Compensation Commission includes holes, tears, cuts, snags or embedded materials in its removal criteria .

2.3 Embedded Materials

A related concern is embedded materials—particles, metal fragments, or debris lodged in the webbing. The CCOHS lists crushed webbing or embedded particles as conditions that make a sling unusable . These embedded materials can cause internal abrasion during lifting, progressively weakening the sling from within.

3. Stitching Failure: The Most Critical Inspection Point

Stitching is the most highly stressed component of a flat sling. The load-bearing splices and eyes carry the full load, and stitching damage is often the first indicator of imminent failure.

3.1 What ASME B30.9 and OSHA Require

Per ASME B30.9-2021, Section 9-5.9.5(e), a synthetic webbing sling shall be removed from service when broken or worn stitching in load-bearing splices is present . OSHA 29 CFR 1910.184(i)(9)(iv) uses identical language .

The CCOHS lists broken or worn stitching as a condition that makes a synthetic web sling unusable . Workforce Safety includes broken or worn stitches in its removal criteria .

3.2 Types of Stitching Damage

• Broken stitches —one or more threads in the eye or splice area have broken. Immediate retirement.

• Worn stitching —the stitching has abraded and appears thin or frayed. Immediate retirement.

• Stitching pull-out —the stitching is separating from the webbing. Immediate retirement.

• Uneven or distorted stitching —may indicate overload or manufacturing defect. Inspect carefully.

The Maine Department of Labor guide notes that when a significant number of fibers in the stitching are broken, the sling should be taken out of service .

3.3 Real-World Consequence

OSHA citations demonstrate the severity of ignoring stitching damage. In Martin Automatic, Inc., a synthetic web sling with snags, punctures, tears, cuts, and broken/worn stitches was used to unload steel bundles—exposing employees to crushing hazards . In Wickham Industries, Inc., a web sling with broken and worn stitching was used to move glass panels weighing more than 8,000 pounds, resulting in a Serious violation with a $6,951 penalty . In ASAP Installations LLC, a synthetic web sling with visible broken and worn stitches was used for rigging corner pieces .

Lishenflex's manufacturing process includes load-bearing stitching with high-tenacity polyester thread, inspected at multiple stages to ensure splice integrity. Our field data show that stitching failure is the most common cause of sudden sling failure—which is why we emphasize stitch inspection in all our training materials.

4. Inspection Protocol: What to Check and How Often

4.1 Pre-Use Inspection (Before Every Lift)

Per ASME B30.9, the operator or designated person must perform a visual inspection before each use :

• Identification tag —present and legible?

• Webbing surface —any cuts, snags, punctures, or tears?

• Edges —any edge damage or broken fibers?

• Stitching —any broken, worn, or pull-out stitches?

• Fittings —any distortion, cracks, or corrosion?

4.2 Frequent Inspection (Daily or Each Shift)

For slings in severe service conditions—high temperatures, chemical exposure, heavy loads—ASME B30.9 requires frequent inspections conducted by the operator or designated person .

4.3 Periodic Inspection (At Least Annually)

ASME B30.9 requires that a qualified person perform a complete periodic inspection at least annually for normal service, and monthly to quarterly for severe service. The inspection must include all removal criteria and be documented .

CERTEX Denmark adds that slings should be visually examined at least annually by a competent person to establish fitness for continued use, and records of such examinations should be maintained .

5. Summary and Practical Recommendations

Spotting cuts, snags, and stitching failure in flat slings is not about looking for obvious damage—it is about knowing exactly what to look for and applying clear removal criteria.

Key takeaways:

1. Cuts and tears —remove from service if they expose load-bearing fibers or reduce webbing width

2. Snags and punctures —remove from service; they disrupt the weave and concentrate stress

3. Stitching failure —broken or worn stitching in load-bearing splices requires immediate retirement

4. Inspect before every use —ASME B30.9 and OSHA require it

5. Document inspections —maintain records per ASME B30.9 requirements

6. When in doubt, scrap it out —a replacement sling costs far less than a dropped load

Lishenflex manufactures polyester flat slings to EN 1492-1 and ASME B30.9 standards, with load-bearing stitching of high-tenacity polyester and clear color-coded capacity markings. Our products are available in single-ply, double-ply, and multi-ply configurations, with widths from 25 mm to 300 mm.

If you need assistance establishing a flat sling inspection program—or need help determining whether your current slings meet ASME B30.9 removal criteria—please send an email to sales@lishenflex.com, and our technical team will provide one-on-one support.