Editor’s note: NATE’s TowerTimes ran an article in this month’s issue they have invited Inside Towers to share with our readers. The author is Caleb Messer with help from the members of the PAN Advisory Group: Craig Snyder, Jeremy Buckles, John Erichsen, Ken Hill, Michelle Kang, Marianna Kramarikova, and Scott Kisting. Due to the length and detail of the article, we will present it in two parts. (part two will continue in tomorrow’s issue)
At the time of writing, there are multiple rope and rigging subcommittees that are currently working to improve training and communications, refine standards and best practices, and consult equipment manufacturers for product innovations. These committees are made up entirely of volunteers that are investing their time and talent to ensure the workforce has access to the knowledge that, when applied, will ensure that the industry becomes a safer place.
This article is intended to continue this momentum, and complements the recent document about the basics of rope selection, characteristics, and usage. Improved familiarity with existing regulations, standards, and best practices for rigging with synthetic rope should serve as a good starting point in the development of training, sound operating procedures, and equipment selection. This document will address the most common pieces of equipment used as part of a rigging system in telecommunications work: capstan hoists, synthetic rope, blocks, shackles, and synthetic slings.
Please note, this article is not intended to be an all-inclusive list and does not attempt to cover all equipment, jobsite-safety, or rigging fundamentals.
For means and methods, the ANSI/ASSP A10.48 Standard should be consulted along with other standards and regulations that may apply to the specific work environment.
- ANSI A10.48
- ASME B30.26
- ASME B30.30
- Cordage Institute CI1401
- ASTM F1740
- ISO 16625
A chain is only as strong as its weakest link. The same is true for a rigging system. The ANSI/ASSP A10.48 and ASME B30 Standards do an excellent job of requiring and clarifying the Working Load Limit (WLL) of the system components. Information about the WLL requirements of each component and the source of those requirements is below. Industry best practices are to ensure the WLL of each of the components below exceeds the maximum rated capacity of the hoist/ winch which will be used in a lift.
It should be noted that establishing the WLL for synthetic rope used in our industry for hoisting applications is specifically addressed in the ANSI/ASSP A10.48 due to the simple fact synthetic ropes are not currently addressed within other recognized consensus standards for this particular application. It is therefore essential for those working with synthetic ropes to be trained and knowledgeable on the requirements for properly determining the applicable WLL using a minimum gross 10:1 safety factor applied to the rope manufacturer’s published minimum breaking strength (MBS) which builds in efficiency losses up to 50% for typical knot terminations and wrap efficiencies thus netting an effective safety factor no less than 5:1.
Synthetic slings require a minimum 5:1 safety factor in accordance with the ASME B30.9 with the rated WLL based upon the type of sling hitch. Shackles Standard shackles used in our industry require a minimum 5:1 safety factor in accordance with the ASME B30.26. Blocks Rigging blocks require a minimum 4:1 safety factor in accordance with the ASME B30.26.
The establishment of minimum safety factors for each of the rigging components is only beneficial if those in the field fully understand the loading demands and are able to clearly discern the rated capacity for each component within the system. As a result, the standards which dictate the safety factors have also generated labeling requirements which are intended to eliminate accidental overloads. Below are the labeling requirements for each of the components. One additional note – the labels must be legible throughout the service life of the product. If a label becomes illegible or is removed from the product, it must be removed from service.
The ANSI/ASSP A10.48 doesn’t specify labeling requirements for rope, but does require that “Synthetic rope shall not be used unless there is documentation available verifying its minimum breaking strength (MBS).” The commonly accepted best practice at this point is that the rope is tagged with the MBS, production date, original length, and diameter.
ASME B30.9 requires that synthetic slings be marked with the manufacturer’s name or trademark, material composition of the sling, manufacturer’s code or stock number, and the rated WLL in at least one hitch type; although, standard practice is to clearly label the WLL for vertical, choked, and basket hitch configurations.
ASME B30.26 mandates that the shackle body be durably marked with the name or trademark of the manufacturer, the rated WLL, and the size. Additionally, the shackle pin must be labeled with the name or trademark of the manufacturer, and the grade, material type, rigging blocks used in our industry with labeled compatible rope sizes of ½” and an inner sheave diameter slightly below 3” still meet the minimum 6:1 ratio when used with double-braid and kernmantle ropes.
Sheaves for Synthetic Rope vs. Wire Rope
With regards to the sheave groove profile, the ANSI/ASSP A10.48 states, “The size of the synthetic rope shall be compatible with the sheave groove in the rooster head and rigging blocks. Groove widths shall be greater than or equal to 1.10 times the rope diameter.” This requirement is one of the primary reasons why blocks may be categorized as either wire rope or synthetic rope blocks.
The narrower groove on the sheave of wire rope blocks introduces significant risk of rope milking or binding as it passes over the block. The wider groove enables the rope to spread over the sheave as it passes over the block enabling a smooth transition.
and/or WLL rating. The ANSI/ASSP A10.48 Standard further dictates that the WLL be provided in pounds or tons.
September 5, 2019