The strength ratings for climbing gear exist to give you information about the limitations of the equipment. Without exception, the strength rating of all climbing gear indicates the maximum load the gear endured prior to destructive failure using standard testing procedures. Under no circumstances should strength ratings be interpreted as a safe working load.
If you examine your climbing gear you will find some cryptic diagrams etched on it or included on the labels and hangtags. This information offers details about the gear’s strength (in kiloNewtons) and manufacturing procedures.
A kiloNewton (kN) is a measure of force, rather than a measure of static weight or mass. Force is calculated by multiplying mass by acceleration. One kiloNewton equals approximately 100kg when the accelerating force of gravity is acting on it. Pieces of equipment that are designed to absorb the force that a fall generates (these include rope and webbing, your harness, and all gear used as anchors or protection on a route) will be rated with the maximum number of kiloNewtons they can withstand. These ratings do not take into account factors such as wear and deterioration, cross-loading or levering.
An older method for strength testing had an arbitrary, though universally accepted, margin that rated biner strength at 10% below the average failure point of a test batch.
In other words, by pull testing a random sample of carabiners and measuring the average failing point and subtracting 10% of the average strength, the manufacturer can predict within an acceptable margin of accuracy and safety that the product will endure the impact forces generated by a falling climber.
To attain a meticulous degree of accuracy, some manufacturers use a rigorous rating standard called Three Sigma:
For example, if 20 carabiners fail with an average strength of 2700 kilograms with a standard deviation of 65 kilograms, the Three Sigma rating would be 2505 kilograms (3 x 65 subtracted from the average strength). The Three Sigma standard tells us that more than 99% of the carabiners produced will endure more than 2505 kilograms of weight before failure.
Most quality climbing products meet widely accepted standards of quality and safety. Although it is not explicitly required by law in North America, Some of the standards you will see associated with climbing products are: CE, UIAA, and ISO.
A product stamped with the CE mark indicates that it has passed strength testing requirements, and the manufacturing processes meet European Union laws. The CE mark is accompanied by a number (for example CE 0639) that identifies the registered testing facility the company uses. The standards that products need to be tested to are identified by “EN”; for example EN 959 covers rock anchors.
In Europe, all climbing products in defined categories must receive CE certification before they can be sold.
CE standards are based on the pre-existing UIAA had norms that climbing equipment manufacturers referred to before CE testing was implemented.
Today, the UIAA norms still exist and often lay out additional (though voluntary) requirements for certain products. For instance, the UIAA helmet rating calls for even higher force absorption standards than the applicable CE norm. Products that meet the UIAA norm have been tested in UIAA approved facilities and have the UIAA stamp.
Many non-European climbing manufacturers seek both CE and UIAA certification in order to sell in the European market and demonstrate the quality of their products to consumers in North America.
ISO is an international standards organization. Manufacturers that are ISO certified have a registered facility oversee their quality assurance systems to make sure they conform to the norms.
Note: Not all climbing product categories have established standards. It is also possible that advancements in manufacturing technology and product innovation will temporarily out-pace the UIAA and CE regulatory boards.