Safe Use of Fiber Rope
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Cordage Institute International Guideline CI 1401-06 • Safer Use of Fiber Rope • May 2006 1. Overview 2. Minimum Breaking Strength 3. Working Load / Working Load Limit 4. Design Factors Commercial and industrial users must determine a DF based on actual service conditions and establish operating procedures for a specific application. A “general use” consumer must also assess his application and determine conditions of use and hazards that may apply. As a rule, the more severe the application, the higher the DF needs to be. Selection of a DF in the general range between 5:1 and 12:1 is recommended. A design factor at the low end of this range should only be selected with expert knowledge of conditions and professional estimate of risk. DF at or above the high end of the range should be used for more severe conditions of use. When in doubt, always select the highest practical DF, or contact the manufacturer for additional guidance. Engineering assistance may be necessary to determine the service loads and risks and to set the appropriate DF. Considerations in the Selection of a Design Factor • Experience is the best guide for determining a DF. Select a DF value used in a similar application that proved successful.• Consider increasing the Design Factor if: - Problems have previously been observed in similar applications - Injury, death or loss of property may result if rope fails - Loads are not accurately known - High or continuous dynamic loads are anticipated (See Section 6) - Shock loads are anticipated - Extensive cyclic loads are likely to occur - Tension is on the rope for long periods - Knots are used, as knots can reduce strength by as much as 50% - Operators are not well trained - Operation/use procedures are not well defined and/or controlled. - Severe abrasion is likely to occur from exposure to rough surfaces or cutting edges, or by contamination from dirt and grit.
5. Calculation of Values Similarly, the Working Load Limit of a new rope is determined by dividing the Minimum Breaking Strength by the Design Factor for a given application. MBS?DF=WLL. Examples of WLL, based on a DF of 5:1 and 12:1, are given in individual Cordage Institute Standards. The WLL in CI standards are for new ropes with standard terminations. 6. Dynamic Loading Users should also be aware that dynamic effects are greater on a low-elongation rope, such as manila, than a high-elongation rope, such as nylon. Also note that dynamic effects are more significant on short segments of rope as opposed to longer ones. Excessive dynamic loading will shorten the life of a line and/or cause premature failure. 7. Recoil/Snapback Safety Warning 8. Special Applications In addition to the above, more specific guidelines should be considered for applications such as life safety and marine use. |
