CRANECRITIQUECORNER
SYNTHETIC SLINGS
PROPER INSPECTION AND SAFE USE This month’s topic:
by: Dave Barnhouse
A monthly crane and rigging informative column for all personnel directly or indirectly involved with crane safety. Each month we will attempt to explain a different technical issue pertaining to crane operations here on Guam, addressing the sometimes overlooked or misunderstood topics by management and operators alike, by Dave Barnhouse Synthetic slings are popular for two, primary reasons: they are user and load friendly. While synthetic slings are available for most any capacity lift, they also protect loads from damage that wire rope or chain may cause making the same lift. However, though the load may not be damaged, often the sling is damaged, even if minimal. This is where inspection criteria of wire rope and synthetic slings differ greatly and the end user must be aware of these differences. ASME B30.9 (Slings) Para 9-5.10.2 (d) states: Sharp edges in contact with the sling should be padded with material of sufficient strength to protect the sling. OSHA states in 1926/1404 (r) (2): When rigging is used for assembly or disassembly of cranes: The employer must ensure that synthetic slings are protected from abrasive, sharp or acute edges, and con-figurations that could cause a reduction of the sling’s rated capacity, such as dis-tort ion or localized compression. Actually, this rule applies whenever using synthetic slings, not merely when assembling or disassembling a crane. This paragraph may have been added to the new crane ruling with emphasis on crane assembly after the New York tower crane incident where a synthetic sling failed while placing a wall tie tower bracket. The bracket slid down the tower breaking the next bracket loose and continued breaking all the lower brackets until an unsupported tower crane remained well over the height limits for a free standing crane. What resulted was the entire crane lying in the street with several fatalities and millions of dollars in damages. All of this because of a non-protected synthetic sling from a sharp edge. The effects of a sharp edge on a tensioned synthetic sling cannot be overstated. This is perhaps the number one way synthetic slings are abused. In the classroom I demonstrate this by comparison of pack-aging tape and a sling. Packaging tape is also a synthetic material, very thin, and very strong. When taping up a package to mail we tension the tape and then poke it with 28 | FEBRUARY2012
Besides the improper use with low horizontal to sling angle and tip loading the hook, this sling should be taken out of service because of the damaged webbing. a pen and a clean break results. If you poke the tape without tensioning first it just doesn’t work the same. This is the same principle of synthetic sling failure when tensioned over a sharp edge. The edge does not need to be particularly sharp to damage the sling, nor does the load need to be particularly heavy. I have a 17,000 lb. capacity web sling in the classroom for demonstrative purposes that was cut into half while in a four-leg bridle configuration and lifting a 4,000 lb. air conditioner. If you do the math it is easy to see if all legs were equal this hitch should have had 1,000 lb. tension on each leg. With the 5:1 safety factor calculated this sling should have close to 85,000 lb. breaking strength. How did 1,000 lb. tension break a sling with
85,000 lb. breaking strength? The answer is the sling softener fell out, the operator nor the rigger noticed it and resulted in the sheet metal acting as a knife. The rigging 5:1 safety factor exists for this reason, however, even this is not enough to prevent a knife-like cut. No operator or rigger should ever have witnessed a sling failure other than testing to destruction which is not very likely. If a broken sling, whether wire rope or synthetic, is found on a job site broken and discarded, a thorough investigation should be made because this sling has been abused and/or overloaded. There is a weak link in the lifting chain and this creates a definite hazard. It must be
This month’s test quiz addresses: Working near Power Lines
May a crane operator ever intentionally work closer than Table A Zone (10 feet) to an energized power line?
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