Power lifters

Proper lifting and rigging techniques can help make work safer and more productive

Lifting building materials on a jobsite is key to advancing the job. But it can also be one of the most dangerous aspects of the job as well.

The National Center for Construction Education and Research (NCCER) has developed some guidelines for lifting and rigging that can help workers get their jobs done safely and productively.

While this article highlights important facets of rigging and lifting, the site engineer should be consulted on lifting extremely large items or those with odd shapes and challenging centers of gravity.

Slings are the most common lifting devices used on jobsites. They can be made from chain, wire rope, metal mesh, natural fiber rope, synthetic fiber rope or synthetic web.

The strength and wear characteristics of each sling type depends upon the material from which they are made and should be selected based on those characteristics and the size, weight, shape, temperature and sensitivity of the building material being moved.

Chain slings
Chain slings are commonly used because of their strength and ability to adapt to the shape of the load. However, alloy chain slings can be damaged by sudden shocks.

Chain slings can be used to lift materials as hot as 1,000 F, but alloy slings must be de-rated for load capacity if temperatures exceed 600 F. You can find the sling’s capacity on the identification tag or other identification method on the sling. Wear parameters are found in tables in OSHA standard 1910.184.

All slings must be inspected before use, and chain slings must be cleaned before each inspection because dirt and oil may hide damage. Alloy steel slings may stretch under heavy load, so look for stretched links that exceed manufacturer specifications. Look for nicks or gouges; if you find any, remove the sling from service.

Sling inspectors should check to assure the chain has not stretched more than three percent of its new length. If any link has stretched beyond this limit, it is unsafe and must be discarded,

If links bind, check for wear on the inside radius of the links by pushing links together to expose the inside link radius.

If heavy nicks or gouges are found, they must be filed smooth and then measured with calipers and compared with the minimum allowable safe dimensions. If in doubt, do not use the sling.

Never weld a sling to repair it.

Wire rope slings
Wire rope slings are made up of individual wires that form strands and are twisted into wire ropes. Fiber-core wire ropes are easier to handle, but are also easier to damage. A wire rope core cable, although harder to handle, offers greater strength and resistance to heat damage.

Wire ropes are further defined by the lay or the direction the wire is wound around the core. A right lay rope is wound in the same direction as a conventional screw thread; a left lay is the opposite.

Further, if the wire in the strand is wound in the opposite direction as the lay of the rope, it is known as a regular lay rope. If the wires are twisted in the same direction as the strand, it is called a lang lay rope.

A regular lay wire rope resists kinking and twisting and is easy to handle. It can withstand crushing and distortion forces.

Lang lay ropes are recommended for drag, hoist and dredge lines. They have greater surface area than regular lay ropes and are more flexible because the outside wires lie at an angle to the rope axis.

The rotation of a left lay rope tightens as it wraps around a standard coupling, so it is a popular choice for use in oil field rod and tubing lines, blast hole rigs and spudders.

Wire rope sling selection must be based on its strength and its ability to bend and withstand wear and abuse. Its strength is measured by its maximum load limit divided by an appropriate multiplier. New wire rope slings have a multiplier of 5; however, well-used slings’ ultimate strength is proportionately reduced. Older slings must be rigorously inspected because even slight damage will affect its ultimate strength. Blocking or padding can reduce wire wear and fatigue.

Abrasion also affects wire rope strength. Abrasion resistance depends on the size, number of wires and construction of the rope.

Other abuse can affect the wire rope’s capacity and will show up in a wire rope as kinking or bird caging, where the rope strands are forcibly untwisted and spread outward.

Like chain slings, wire rope slings must be cleaned before inspection. Remove any dirt or oil that could hide damage.

Look for broken or damaged wires; if 10 randomly distributed wires in one lay are broken or five wires in one strand of a rope lay are damaged, the sling must not be used. The inspector should also check end fitting and component condition.

Operators are key in an effective sling inspection and use program. If a lifting accident occurs, it must be investigated before lifts continue. 

Wire ropes slings must be lubricated to assure long use life. There is no set rule on how much or how often this should be done. In general, the heavier the load, the greater number of bends and the more adverse the working conditions, the more frequently lubrication should be completed. Before lubricating, make sure the sling is dry, because lubricant may trap moisture.

Wire rope slings should be stored in a well-ventilated, dry building or shed. Never store them on the ground or allow them to be continuously exposed to weather.

Using slings several times a week, even under light load, is a good idea because frequently or continuously used slings last far longer than those that are not used.

Discard a wire rope sling if it has severe corrosion.

To double-check the capacity of wire rope slings, refer to OSHA standard 1910-184, Tables N-184-3 through N-184-14. If the cable rope sling you are using is not found in these tables, follow the manufacturer’s recommendations.

Fiber rope/synthetic web slings
Fiber rope and synthetic web slings are used for temporary work in construction or painting jobs and in marine applications. They are the best choice for lifting expensive, highly finished, fragile or delicate loads. These slings may be used without de-rating in temperatures from -20 F to 180 F, unless they are wet and frozen.

Fiber ropes and synthetic webs are pliable, grip the load well and will not mar the load’s surface. Do not use them on loads with a sharp edge that may cut the sling fibers. They should not be used in highly abrasive applications, high temperatures or acidic environments.

Three-strand fiber ropes must follow the OSHA standard 1910-184 capacity ratings found in Tables N-184-4 and N-184-5. If the sling is not covered in these tables, follow manufacturer’s recommendations.

Rope type and size is based on the application, weight to be lifted and sling angle. Inspect fiber ropes often because they deteriorate faster than wire rope slings. 

Fiber rope slings should not have any brittle, scorched or discolored fibers. If any are found, contact a supervisor who can judge whether it can be used.

The interior of the sling should be as clean as when the rope was new. If powder-like sawdust has built up on the inside of the sling, it has worn excessively and may mean the sling is unsafe. Finally, scratch the fibers with your fingernail. If fibers come apart easily, the sling should be discarded.  If a sling has been spliced, it cannot be used unless it meets the minimum requirements of OSHA standard 1910-184 and any other manufacturer recommendations.

Synthetic web slings
Made of nylon, Dacron or polyester, synthetic web slings offer many rigging advantages. They can handle loads up to 300,000 lbs., can conform to any shape, and will adjust to the contour of the load and hold it with a non-slip grip without marring. They have a low initial cost and a long service life. They can absorb heavy shocks without damage and are unaffected by temperatures up to 1,800 F. They are also resistant to certain chemicals.

Nylon slings can be used in alkaline or greasy conditions, but they are also often used in neutral conditions. Dacron and polyester are the best choice when working around high- acid or high-temperature bleach solutions and where stretching must be minimized. In alkaline environments, use nylon or polypropylene slings.

Take any synthetic sling out of service if it shows signs of acid or caustic burns; surface melting or charring; snags, punctures, tears or cuts; broken or worn stitches; distorted fittings or wear or elongation that exceeds manufacturer specs.

Metal mesh slings
You can identify sling capacity on metal mesh slings by checking the permanently attached durable marking that shows the rated capacity. It should identify vertical basket hitches and choker hitch loadings.

If any metal mesh sling has a coating applied or been repaired, it must be proof-tested for the rated capacity. You can find rated load capacities for various metal mesh slings in OSHA Standard 1910.184, Table N-184-15. Slings not in this table must follow manufacturer’s recommendations. Do not apply coatings that could affect the sling’s rated capacity.

Any sling repairs must be recorded. Note the date, nature of repair and the person or organization performing the repairs. Metal mesh slings should be taken out of service if there is a broken weld or brazed joint along the sling edge; reduction in wire diameter of 25 percent due to abrasion or 15 percent due to corrosion; inflexibility from fabric distortion; enough distortion of the female handle so the slot depth increases by more than 10 percent; distortion of either handle width so the eye width decreases more than 10 percent; or a 15 percent reduction of the original cross-sectional area of the metal at any point around the handle eye or distortion of either handle out of its plane.

Published in the March/April 2006 issue of Contractor Tools and Supplies magazine.

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