Know Your Ropes
The old rock group “The Band” came out with a song in the late sixties called “The Weight.” The lyrics tell us to unburden our weight and “put the load right on me.” No doubt all of the major rope manufacturers have thought about buying the rights to that song. Teufelberger, Samson, Sterling, Bridon, Marlow, Yale Cordage and others go to great lengths (no pun intended) to give detailed information on elongation, tensile strength, weight, and much more. According to Kathy Gill, President and Founder of Tower Safety, as users, if we are “putting the load” on our ropes, we need to understand how they will be implemented and what we expect them to lift. Gill broke down the various functions and types of ropes available for Inside Towers.
Working Loads characterizes a range of rope from proper use, rope conditions, exposure to several factors affecting rope behavior, and the degree of risk to life and equipment involved. Working loads are based on new, unused rope in excellent condition and being used in non-critical applications and under normal conditions. If injury to people or damage to equipment exist, working loads should be reduced. Working loads must never increase past the given guidelines of the rope manufacturer. If a tower crew’s rope has been subjected to dynamic loading, high temperatures, long periods of loads, extreme stress, improper storage/use, or fails a rope inspection, the rope must be taken out of service.
Dynamic loading occurs when rope is subjected to sudden or extreme stress such as abrupt starting or stopping of a load. The effect of dynamic loading is greater on low-elongation rope, such as polypropylene than on high-elongation rope, such as nylon. The rigger will need to consider time-delayed friction, a transition from a low friction to strong friction near the force maximum, which leads to a fast relaxation of the rope. If a load is applied too quickly to a synthetic device (e.g., sling), heat due to friction can be enough to melt or degrade some of the material. A lifting system might have different parts which share the load forces, but which react to those forces at different rates. If the load share on the rope core is applied or released too fast, then the core of the rope no longer shares load with the strands and the resulting imbalance can cause the rope to have a hernia.
Tensile strengths are determined from tests on new, unused rope in accordance with standard test methods of the Cordage Institute, 994 Old Eagle Schoolhouse Rd., Suite 1019, Wayne, PA 19087.
OVERLOADING: ROPE USE & CARE
Avoid sudden strain. When a working load has been used to select a rope, the load must be handled slowly and smoothly to minimize dynamic effects and avoid exceeding the provision for them.
All rope will be severely damaged if subjected to rough surfaces or sharp edges. Chocks, winches, drums and other surfaces must be kept in good condition and free of burrs and rust. Pulleys must be free to rotate and should be of the proper size to avoid excessive wear. Keep the rope clean. Dirt and grit will act as an abrasive and will damage the rope fibers.
Never stand in line with rope under tension. Should the rope fail, it will recoil with considerable force. This could cause serious injury to persons or property anywhere in the vicinity. This danger can exist from failure of fittings within the rope’s safe working load. Check all fittings, bolts, shackles, splices and so forth before using.
Synthetic ropes can lose up to 50 percent of their strength when used or stored at temperatures above 140 degrees Slippage or surging on a capstan or winch will cause localized overheating, resulting in severe loss of tensile strength. Consult the manufacturer for recommendations as to the size and type of rope for a proposed continuous heat exposure condition.
KNOTS & SHARP BENDS
Tying knots and creating sharp bends can decrease rope strength by as much as 50 percent. Use the manufacturer’s recommended splices and avoid sharp bends for maximum efficiency.
Most synthetic ropes are resistant to oil, gasoline, paint, and most chemicals. Natural fiber ropes can be severely damaged by exposure to chemical fumes or actual contact. Consult the manufacturer for specific chemical exposure.
Synthetic ropes may be weakened by prolonged exposure to ultraviolet rays or extreme heat. Store out of direct sunlight in a cool, dry and well-ventilated place. Never coil rope as a garden hose or around a chair to get the “perfect” oval shape. Rope has a natural tendency to twist and should be coiled appropriately to avoid that spiral will occur and kinking is likely. Torsions are put into the rope by every loop that is pulled off, and the rope becomes twisted and unmanageable.