Carabiners, small metal ovals with opening gates, are used extensively in rock climbing and mountaineering as a connection between the rope/climber and the protection attached to the rock wall/ice sheet. Engineering advances in the last twenty years have enabled carabiners to become far lighter, an advantage when weight is an issue and each additional ounce is counted. With this new technology, however, comes the question, how safe are these carabiners for climbing?
To answer this question, ETH Zurich materials scientist Thomas Schambron has analyzed both the passive and dynamic forces sustained on rock climbing carabiners, as well as the effects of typical wear and tear, in the most in depth safety study of its kind. There many different types of carabiners with multiple features. Common carabiners are made of aluminum alloy, have locking, screw-locking, safety-locking, bent, straight or wire gates, and less common, heavier, steel alternatives. The problem with having variable carabiners is that each is a tradeoff between function, weight, and safety.
Carabiners with locking gates are harder to use, but will not open accidentally and vice-versa. Carabiners with open gates are dramatically weaker than if the gates are closed. Aluminum carabiners are lighter, but cannot sustain the forces that a steel oval would. The standard strength tests, in addtion to these problems, did not account for the dynamic force applied to the carabiners when a climber falls onto them, rather, tested a static force. This has allowed for carabiners to pass safety minimums, despite being unsafe in certain scenarios.
After testing carabiners both statically and dynamically, Schambron found that the breaking point of a dynamically loaded carabiner is much lower than that of a statically loaded device. Due to the fact that curent safety tests only require a static test to hold 20 kilo-newtons (kn) of force, he concluded that dynamic safety tests are critical for carabiners to be considered safe. Furthermore, Schambron found that carabiners were at their weakest when the gate is open, which he uses as an argument for using wire-gate carabiners that rarely open accidentally.
Schambron advices that, should you engage in any climbing activity, you should look for steel wire-gate carabiners with open gate strengths of at least 10kn. All carabiners display their longitudinal, horizontal, and open gate strength ratings embossed on the device; however, it is recommended that you seek professional consultation before using any equipment.