Is It Safe to Use a Lifting Slings That Has Been Stored Wet?

A rigging crew finishes a lift on a rainy day. The lifting sling is wet, but it looks fine. The crew tosses it into the storage locker and moves on to the next job. Two weeks later, the sling is retrieved, inspected quickly, and used for a critical lift. The sling fails. The investigation reveals the cause: mildew growth and fiber degradation from being stored wet.

 

This scenario is more common than most rigging professionals would like to admit. According to industry guidance, slings that become wet during use or cleaning must be completely air-dried before storage. Storing a damp sling invites mildew growth and fiber degradation. The Canadian Centre for Occupational Health and Safety (CCOHS) further notes that nylon slings lose 10–15% strength when wet, though strength is restored upon drying.

 

Lishenflex has been manufacturing synthetic lifting slings for over two decades, and our field experience shows that improperly dried slings are a frequently overlooked source of damage and premature failure. Understanding the risks of wet storage is essential to maintaining sling integrity and ensuring safe operation.

 

Moisture Risks

The primary risks associated with storing lifting slings wet include:

 

Fiber Swelling and Dimensional Changes

 

Nylon is a hygroscopic material—it absorbs moisture from the environment. According to Wikipedia's entry on nylon, nylon absorbs moisture in the range of 2–8% by weight depending on humidity and temperature. This absorption causes the fibers to swell, which can affect sling flexibility and fit in fittings.

 

Strength Loss

 

The CCOHS identifies that nylon slings can lose 10–15% of their strength when wet, though strength is restored upon drying. Oregon OSHA further notes that nylon slings may lose up to 25% of their strength when wet due to moisture absorption. Polyester slings, by contrast, are not significantly affected by moisture but can suffer from other forms of degradation such as mildew if stored damp.

 

Mildew and Rot

 

Perhaps the most significant long-term risk of wet storage is mildew and rot. According to Wikipedia's entry on mildew, mildew is a form of fungus that grows in damp, warm, and poorly ventilated environments. When slings are stored wet, mildew can grow on the surface and between the fibers, causing progressive degradation of the fiber structure. The CCOHS specifically identifies mold, mildew, and rotting as conditions that weaken the sling and require immediate removal from service.

 

Material-Specific Vulnerabilities

Not all synthetic sling materials react the same way to moisture. Understanding the differences is critical for proper sling care.

 

Source: CCOHS Synthetic Web Slings Guide; Oregon OSHA

 

As the table shows, nylon slings are most vulnerable to strength loss when wet, while polyester slings are more vulnerable to mildew if stored damp.

 

Lishenflex's lab data confirm that nylon slings tested wet show a 12–18% reduction in breaking strength compared to dry samples, reinforcing the importance of drying nylon slings before use. Polyester slings, by contrast, show minimal strength variation between wet and dry states but can develop mildew if left damp for extended periods.

 

Inspection After Wet Storage

Before a wet-stored lifting sling is returned to service, a thorough inspection is required. Per ASME B30.9, slings must be inspected for conditions that could affect their safe use. After wet storage, focus on:

 

Surface Inspection

 

• Discoloration—dark spots or staining may indicate mildew growth

• Surface fuzziness or slipperiness—may indicate fungal growth

• Unexplained stiffness—may indicate fiber degradation

 

Tactile Inspection

 

• Bend the sling—listen for crackling sounds that may indicate fiber damage

• Feel for soft or uneven areas—may indicate mildew damage between layers

• Check for unusual odors—musty smell indicates mildew growth

 

Tag Condition

 

Identification tags—must remain legible. If the tag is damaged or illegible, the sling must be removed from service as the WLL cannot be verified.

 

Critical note: Per ASME B30.9, any sling with visible mildew, rot, or mold must be removed from service immediately. If you suspect mildew growth but are unsure, err on the side of caution and remove the sling from service.

 

Proper Drying and Storage

The best way to prevent wet storage damage is to never store a wet sling.

 

Drying Procedure

 

According to industry best practices:

 

• Wipe down the sling with a clean, dry cloth to remove surface moisture

• Hang or lay flat in a well-ventilated area

• Keep away from direct sunlight—UV radiation can damage fibers

• Keep away from heat sources—temperatures above 90°C (194°F) can permanently damage fibers

• Allow complete air drying before storage

 

Storage Conditions

 

Per CCOHS and Lishenflex recommendations:

 

• Cool, dry, well-ventilated area

• Away from direct sunlight, steam pipes, open flames, and chemical fumes

• Off the floor—on pallets or racks to prevent moisture absorption

• Temperature-controlled—avoid areas prone to condensation or dampness

 

Moisture Testing

If you are unsure whether a lifting sling has been dried sufficiently, perform a simple moisture test:

 

1. Touch the sling—it should feel dry to the touch

 

2. Squeeze the webbing—no moisture should be visible or felt

 

3. Weigh the sling (if possible)—a heavier sling may indicate retained moisture

 

4. Check the storage environment—if the storage area is damp, the sling may have absorbed moisture from the air

 

Summary and Practical Recommendations

Storing a lifting sling wet is not just a minor oversight—it can lead to mildew growth, fiber degradation, and in the case of nylon, significant strength loss. A sling that has been stored wet and shows any signs of mildew or rot must be immediately removed from service.

 

Key takeaways:

 

1. Nylon slings can lose up to 25% of their strength when wet—strength is restored upon drying, but mildew damage is permanent

 

2. Polyester slings are not significantly weakened by moisture—but mildew can grow on the fibers if stored damp

 

3. Mildew is a form of fungus that grows in damp, warm, poorly ventilated environments—it permanently degrades fiber structure

 

4. Always dry slings completely before storage—this is the single most important step

 

5. Inspect wet-stored slings thoroughly—for discoloration, stiffness, odor, and mildew

 

Lishenflex manufactures polyester lifting slings that are less affected by moisture than nylon, but we still emphasize that proper storage is essential for sling longevity and safety. We offer guidance on drying procedures and inspection protocols to help your team avoid wet-storage risks.

 

If you need assistance establishing a sling drying and inspection protocol for your operation—or need help determining whether a wet-stored sling is still serviceable—please send an email to sales@lishenflex.com, and our technical team will provide one-on-one support.