78 pear-shaped carabiner can fit into the wide opening of a Wil- liam carabiner. As the climber returns to face forward, the in- serted carabiner can impart a torque that attempts to rotate the William carabiner about its long axis. Popall (2003) observed a figure-eight-induced torque break the barrel of carabiners. It was unclear why used, but not new, Ball-Lock carabiners were not as strong, in both the absolute and relative compari- sons, as Tri-Act carabiners. This did not appear to be related to the observation that all three carabiners with sticky gates were Ball-Lock carabiners, because among Ball-Lock carabiners, the mean strength of those with sticky gates was similar to the re- mainder. During the study, Petzl released a new design of the Ball-Lock gate, so this particular finding may no longer apply. Differences in breaking strength among failure types were also unclear, especially since they were inconsistent with differ- ences in surface roughness among failure types. The small num- ber of body failures contradicted findings of Blair et al. (2005) for which all failures were of the body. Since the carabiners and test methods differed between the two studies, we can only specu- late whether the limited number of body failures was due to the more complex gate mechanisms of carabiners used in the pres- ent study. It is possible that attaching carabiners to a saddle with steel D-rings caused repeated point loading that encouraged body failures, as observed by McKently et al. (2003). In contrast to the McKently et al. (2003) study, we did not observe obvious gouges in carabiners that experienced body failures. Since too few climb- ers indicated the type of saddle they used, it was not possible to speculate whether point loading may have led to body failures. It seems rather unlikely that climbers would be able to predict strength loss by even a careful visual examination of carabiners, unless severe defects existed [e.g., the gouges reported by McK- ently et al. (2003)]. Petzl’s inspection form lists the following de- fects that should be checked for during a visual inspection: cracks, marks, deformation, wear, corrosion. Of these, wear seems to be a less reliable indicator, in light of the weak prediction of strength from surface roughness. We observed wear and marks on all of the used carabiners, but were not able to identify particularly worn carabiners. Blair et al. (2005) similarly doubted the ability to pre- dict retirement of carabiners based on visual cues of incipient failure. It is easy to imagine improper loading that would weaken a carabiner but not impart any obvious surface wear. Since it is difficult to avoid entirely improperly loading carabiners during climbing, we reiterate the importance of future studies to investi- gate longer-term use, as well as use by a greater variety of climbers. Using cycles-to-failure data from Blair et al. (2005), and as- suming that a 90 kg (198 lb) tree climber who falls 1.5 m (4.92 ft) endures approximately 5 kN (1124 lbf) of force (Carpenter Kane and Ryan: Carabiner Strength 2008), a climber could still take more than 3,000 falls before caus- ing failure of the carabiner. [The rated strength of the carabiners tested by Blair et al. (2005) was 24 kN (5,395 lbf).] Doubling the fall distance for the 90 kg climber would still require 238 falls to break one of the carabiners Blair et al. (2005) tested. A climber would likely suffer bodily injury long before taking so many falls. Thus, ordinary wear for a year would not likely reduce strength to the point where a climber would risk breaking a carabiner. Although not included in the analysis because they were of different manufacturers, shapes, and gates, we also tested four carabiners nearly ten years old; each had endured at least three years of daily climbing. None failed below its rated strength, and all appeared to be much more worn than the carabin- ers used for a single year. Neither these carabiners, nor those analyzed in the study showed any signs of deformation prior to testing. Thus, even longer term “normal” use seems un- likely to cause dangerously damaging wear, unless an ob- vious defect is present, or the gate does not close properly. The lack of participation and follow-through among climb- ers was disappointing. Of 41 carabiners distributed, only 21 were returned, and of these, only 12 had usable hours recorded (2 each from 6 individuals). The project originally intended to analyze strength change in rope snaps as well as carabiners, but of fourteen rope snaps that were distributed, only one was returned. Equally disappointing was the apparent lack of general interest in partici- pating in the project. Although many companies initially expressed an interest, only five companies actually participated. Ultimately, only four companies were represented, because no carabiners or snaps were returned from one company. In hindsight, offering par- ticipants an additional incentive, beyond the carabiners and rope snaps each participant received may have increased participation. CONCLUSIONS Carabiners used for a year by climbers were, in general, as strong as new carabiners. Regardless of differences among gate types and shapes for new and used carabiners, none of them broke at less than their rated strength. Neither of these findings, howev- er, should be interpreted to mean that carabiners do not have to be inspected or are safe to use for a year under any conditions. Climbers must take great care inspecting carabiners, especially with respect to proper functioning of the gate mechanism. Ad- ditional testing should be undertaken to address limitations of the present study, including small sample sizes, short duration of carabiner use, and the presumed better treatment of carabiners by knowledgeable, experienced, and safety-conscious climbers. ©2009 International Society of Arboriculture
March 2009
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