Recommened Operating Practices

Diameter & Size Number Values

Size is determined by linear density; diameter is given as a minimal value, that is, it may vary slightly.  If a specific diameter value is specified, linear density and minimum breaking strength values may be different from those given in tables.  Size number is given as a reference.

Working Loads

Minimum breaking strength is based on data from a number of manufacturers and represents a value of 2 standard deviations below the mean, as established by regression analysis.  The working load of a rope shall be determined by dividing the minimum breaking strength by the design factor.  Design factors range from 5 to 12 for non-critical applications.

Because of the wide range of rope use, rope conditions, exposure to the several factors affecting rope behavior, and the degree of risk to life and property involved, it is not realistic to make standard recommendations as to design factors or working loads.  However, to provide guidelines, a range of design factors and working loads are provided for rope in good condition with appropriate splices, in non-critical applications and under normal service conditions. Normal service is generally considered to be used under static or  very modest dynamic load conditions.

Design factors at the low end of the suggested range should only be selected with expert knowledge of conditions and professional estimate of risk, based on the critical conditions of use below.

Critical Conditions of Use

Design factors at the high end of the range or larger shall be used when:

1. Small ropes are used because they can be more severely damaged by cutting, abrasion & sunlight.
2. Loads are not accurately known.
3. Operators are poorly trained.
4. Operation/use procedures are not well defined and/or controlled.
5. Inspection is infrequent.
6. Abrasion, cutting, dirt are present.
7. Shock loads or extreme dynamic loadings are likely.
8. High temperatures are present.
9. Chemicals are present.
10. Ropes are kept in service indefinitely.
11. Tensions on the rope are maintained continuously for long periods.
12. Rope can be subject to sharp bends if used over pulleys or surfaces with too small a radius.
13. If knots are used, strength is reduced by up to 50%
14. Death, injury or loss of valuable property may result from failure.

Dynamic Loading

Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading.  The more rapidly or suddenly such actions occur, the greater this increase will be. In extreme cases, the force put on the rope may be two, three, or even more times the normal load invovled; for instance, when picking up a tow on a slack line or using a rope to stop falling object. Therefore, in all such applications as towing lines, life lines, safety lines, climbing rope, etc., design factors must reflect the added risks involved.

Users should be aware that dynamic effects are greater on a low-elongation rope such as manila than on a high-elongation rope such as nylon and greater on a shorter rope than a longer one.  The range of design factors given contains provision for very modest dynamic loads.  This means that the load must be handled slowly and smoothly to minimize dynamic effects.

Special Safety Note

A dangerous situation occurs if personnel are in line with a rope under excessive tension.  Should the rope fail, it may recoil; with considerable force - especially if the rope is nylon. Death may result. Persons must be warned against standing in line with the rope.

Special Applications

The design factor ranges are not necessarily intended to apply in those applications where a thorough engineering analysis of all conditions of use has been made by qualified professionals.  In such cases, breaking strength, elongation, energy absorption, behavior under long-term or cyclic loading, and other pertinent properties and operating procedures may be evaluated to allow the selection of a design factor best suited to the requirements.

NOTE: Because of the wide range of rope use, rope condition, exposure to the several factors affecting rope behavior, and the degree of risk to life and property involved, it is impossible to cover all rope applications in this section. In all cases where risk is involved, or there is a question about the condition of use, consult the manufacturer. This is not intended to apply to rescue rope.  Consult the manufacturer for specific applications.

CHOOSING A ROPE

Always consult the manufacturer before using rope when personal safety or possible damage to property is involved.

Make sure the rope is adequate for the job.  Do not use too small a rope or the wrong type.  Specifications are available from your dealer, distributor, or the manufacturer, which gives the strength and recommended working loads for various sizes and constructions of hard fiber and synthetic rope.

REMOVING ROPE FROM COILS & REELS

Remove rope properly from coils or reels to prevent kinking.

If the rope is in a coil, it should always be uncoiled from the inside as directed by the manufacturer. If on a reel, the rope should be removed by pulling it off the top while the reel is free to rotate. This can be accomplished by passing a pipe through the center of the reel and jacking both ends up in a horizontal position until the reel is free from the surface.  To proceed in any other manner may cause kinks or hockles (strand distortion).

HANDLING ROPE

Never stand in line with rope under tension. If a rope or attachment fails, it can recoil with sufficient force causing physical injury. Synthetic rope has higher recoil/snapback tendencies than natural fiber rope.  

Reverse rope ends regularly, particularly when used in tackle. This permits even wearing and assures longer, useful life. When using tackle or slings, apply a steady, even pull to get full strength from rope. For maximum safety and economy, always use slings employing an angle of about 45˚.

OVERLOADING

Do not overload rope. Sudden strains of shock loading can cause failure.

Avoid sudden strains - shock loads can exceed breaking strength. Shock loading can cause failure of a rope normally strong enough to handle the load. Working loads are not applicable when the rope is subject to significant dynamic loading. Whenever a load is picked up, stopped, moved, or swung, there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater this increase will be. In extreme cases, the force put on the rope may be two, three, or even more times the normal load involved.  Examples could be picking up a tow on a slack line or using a rope to stop a falling object. However, working loads as given do not apply in all such applications as towing lines, life lines, safety lines, climbing ropes, or the like.

Users should be aware that dynamic effects are greater on a low elongation rope such as manila than on a high elongation rope such as nylon, and greater on a shorter rope than on a longer one. Excessive dynamic loading of a high elongation rope is equally dangerous, because of stored energy which will cause the rope to recoil dangerously if it breaks. When a working load has been used to select a rope, the load must be handled slowly and smoothly to minimize dynamic effect and avoid exceeding the provision for them.

WINCHING LINES

Proper procedures will prevent kinks and hockles in three-strand twisted rope.

Repeated hauling of a line over a winch in a counterclockwise direction will extend the lay of twisted rope and simultaneously change the twist of each strand. As this action continues, strand hockles or back turning may develop. Once these hockles appear they cannot be removed, and the rope is permanently damaged at the point of hockling. If the line is continuously hauled over a winch in a clockwise direction, the rope lay is shortened, and the rope becomes stiff and will kink readily.

CHECKING ROPE FOR WEAR

Avoid using rope that shows signs of aging and wear. If in doubt, destroy the used rope.

No type of visual inspection can be guaranteed to accurately and precisely determine actual residual strength. When the fibers show wear in any given area, the rope should be re-spliced, downgraded, or replaced.  Check the line regularly for frayed strands and broken yarns. Pulled strands should be rethreaded into the rope if possible. A pulled strand can snag on a foreign object during a rope operation.

Both outer and inner rope fibers contribute to the strength of the rope. When either is worn, the rope is naturally weakened. Open the strands of rope (either three-strands or braided) slightly and look for powdered fiber, which is one sign of internal wear. A heavily used rope will often become compacted or hard which indicates reduced strength. The rope should be discarded if this condition exists.