When traveling to different climbing areas, I’m always surprised by people’s differing attitudes toward lead protection. Some feel that even a large piece of well-placed pro in great rock should never be loaded — the classic “leader must not fall” mentality. Other climbers take repeated whippers onto small gear in suspect rock, claiming, “This stuff is made to take this kind of beating.” As in most situations, the reality is somewhere between the extremes. Much has been written about impact force and product ratings, but what does this mean when you’re run out and strung out?The theory.Climbing gear strength is measured in kiloNewtons (kN), a measure of force equivalent to roughly 225 lbs. Typical carabiners have a breaking strength of about 24kN, or 5400 lbs, but most lead protection breaks at significantly lower loads. The standard rope-certification test involves dropping an 80kg mass approximately five meters, on a section of rope about three meters long. The top piece of lead protection in this scenario experiences almost double the force exerted on the rope, so if this fall were to occur in the field, loads approaching 20kN — enough to break even the strongest cams — could in theory occur. Yet gear failure is rare in the field. So what’s the deal?Fall Factors. The “Fall Factor” gives an indication of a fall’s severity, and is calculated by dividing the distance the climber falls by the length of rope between the climber and the belayer. A climbing rope absorbs energy by stretching, and more rope means more energy absorption capacity. When it comes to determining the severity of the forces in the system, the length of rope that catches the fall is just as important as the length of the fall itself. In the lab test, the fall is almost twice the length of rope, giving a Fall Factor that approaches two — the maximum possible. This kind of fall is dangerously harsh even when short, but fortunately it’s extremely rare for a leader fall even to attain Fall Factor one; to do so, the falling climber must end up nearly hitting the ground. Low Fall Factors are one reason why loads in the field don’t reach the hypothetical 20kN mark, but there are other factors of importance. The analysis. Other factors that soften the impact on the system include: • Rope slippage through the belay device. This happens regardless of how hard the belayer locks off. Auto-locking belay devices slip less, but they still reduce the overall force generated by a fall. • The belayer is slightly lifted during a fall. This effect is magnified when the belayer “jumps” into the fall (i.e., soft catches). • Both climber and belayer’s harnesses and bodies slightly deform during the moment of impact. • Dynamic climbing ropes absorb an amazing amount of energy. The maximum impact force most modern ropes allow in the system is well below the threshold for passing certification, meaning they’re very effective at minimizing the forces on your lead protection, and on your body. The reality. In the field loads on lead protection of 6 to 9kN are routinely generated, and forces occasionally run up to around 10kN during extreme falls. Some situations will result in higher impact forces: • Falling past the belay station on a multi-pitch route, which indicates a fall factor greater than one. • Successive falls in a short period of time on the same rope (since the rope temporarily loses some of its stretch after a fall). • Belaying directly off an anchor instead of the belayer’s harness. Actual climbing. Many pieces of climbing gear have breaking strengths in or below the 6 to 9kN range, specifically smaller nuts, micro cams, and carabiners that are cross-loaded or loaded with the gate open. Keep this in mind when climbing above thin protection, manky placements, or when the consequences of gear failure are dire. Here are some tips to keep you safe: • Back up small and dubious protection, or better yet, equalize several pieces using RENE (Redundant, Equalized, and No Extension) when possible. • Watch out for biners with sticky gate action, and placements that might pry open the gate. A biner with the gate open is only about one third the strength of a closed-gate biner. A closed biner with the spine loaded over an edge can easily break, even in a moderate fall. • Never catch and weight the nose of a biner on a sling, hanger, or cable. This can cause it to break under body weight, as there is a tremendous amount of leverage on the spine of the biner. Even with small protection, actually breaking gear is quite rare. It’s far more common for placements to fail from being placed poorly or from rock breaking, than from exceeding the rated strength. Paul Tusting, M.E., has worked as an outdoor-industry engineer, testing and designing new climbing equipment for five years. He’s been an active climber for over 10 years.