308 Kane et al.: Damage Inflicted on Climbing Ropes by Handsaws Table 2. Means (standard deviations) for percent cut (% Cut), percent strength loss (% SL) (both in decimal form), and accelera- tion (m/s2 ) for each rope and blade (abbreviations are in Table 1). Within each classification and read down a column, means followed by the same letter are not significantly different (Tukey’s HSD, P > 0.05). Rope N BLAZE BS PI SB VEL XTC Blade F1 F2 F3 IB ZUy 31 30 30 30 30 30 30 30 31 30 30 % Cut 0.49 (0.37)a 0.39 (0.34)bc 0.35 (0.35)c 0.42 (0.34)abc 0.48 (0.34)ab 0.41 (0.34)abc 0.13 (0.05)a 0.47 (0.21)b 0.13 (0.06)a 0.40 (0.17)b 1.00 (0.00)c DISCUSSION The most important finding is that there is little doubt a climb- er can easily cut through many climbing ropes with a handsaw, which may be more dangerous than realized. Since arborists work with many tools that are extremely dangerous (e.g., chain saws and chippers), climbers could easily underestimate the relative danger of their handsaw. It may also be true that climbers who learned to climb before the use of newer hand- saws with “razor teeth” are less aware of their inherent danger. Although only limited tests were conducted on other blades, they appeared to be less likely to cut through a climber’s rope. Under the controlled conditions of the pendulum, which ap- proximated the force a climber could apply with a sharp tug on his or her handsaw, the study did not completely cut through as many ropes as in the initial tests completed by hand, except when using Zubat blades. This was likely due to each author’s ability to maintain contact of the entire blade length along the rope when cutting ropes by hand. In contrast, the pendulum mechanism maintained a fixed trajectory with respect to the rope. Of blade characteristics that were expected to affect the ef- ficiency of cutting (teeth per mm, blade curvature, and tooth sharpness), curvature may have exhibited greater influence than the others due to experimental protocol. For example, F2 and F3 blades shared the same number and type of teeth, but F2 blades more effectively cut ropes, presumably by virtue of their lack of curvature. The straight blade would be less likely to push the rope since each tooth needs to cut only a slightly deeper kerf in the rope. Observed, though not quantified, a large variation in the horizontal distance ropes moved at the moment of impact, the acceleration data reflect this as well. On a curved blade, each tooth must cut a disproportionately deeper kerf in the rope as the curve meets the rope. If the teeth were not able to cut through the rope quickly enough, a curved blade would eventually push the rope in addition to cutting it. Curvature may be less important than teeth per mm and inherent sharpness of a tooth, however, as demonstrated by the effectiveness of Ibuki and Zubat blades. Even though they have nearly the same curvature as F3 blades, Zubat blades have more teeth per mm and were far more effective cutting ropes. Ibuki blades, on the other hand, had fewer teeth per mm than F2 blades, but similar curvature to F1 blades, and yet they cut ropes as effectively as F2 blades. According to the manufacturer (http://www.silkysaws.com), Ibuki blades are de- ©2009 International Society of Arboriculture % SL 0.48 (0.44)a 0.40 (0.37)ab 0.35 (0.38)b 0.40 (0.37)ab 0.43 (0.42)ab 0.42 (0.39)ab 0.02 (0.05)a 0.52 (0.23)b 0.03 (0.08)a 0.51 (0.19)b 1.00 (0.00)c % SL LS Meanz 0.29 (0.024)a 0.29 (0.024)a 0.26 (0.025)a 0.26 (0.024)a 0.23 (0.024)a 0.28 (0.024)a 0.15 (0.023)a 0.36 (0.024)b 0.15 (0.023)a 0.41 (0.021)b n/a Acceleration 2.96 (0.38)a 3.17 (0.57)a 2.98 (0.52)a 3.04 (0.61)a 2.85 (0.58)a 2.96 (0.55)a 3.08 (0.33)ab 2.95 (0.62)a 3.28 (0.43)b 3.15 (0.54)ab 2.50 (0.39)c z The least squares (LS) mean for % SL is the arithmetic mean adjusted for the covariate % Cut; it is followed by the standard error (in parentheses). y Zubat blades were not included in the ANOCOVA because they completely cut through every rope. signed for heavier cutting. They have fewer teeth per mm and lack several tooth features of Zubat blades, which cut ropes remark- ably well. Regardless of the reason(s) explaining the differences among blades, those differences were much greater than differ- ences among ropes, which highlights the overriding influence of blades with respect to percent cut and percent strength loss. It was expected that smaller diameter ropes (typical of the 24-strand construction) would be easier to cut, especially given the alignment of the blade and the fixed trajectory of the pen- dulum, but the results did not support this expectation. Poison Ivy was less deeply cut than the other 24-strand ropes (Blaze and Velocity), but it is not clear whether this reflected the con- struction of the jacket or simply the slightly larger diameter un- der tension [0.4 mm [0.02 in)]. Since the cover strands for all three 24-strand ropes are polyester, and two of the 16-strand ropes (Safety Blue and XTC) were cut similarly to Blaze, the braiding process itself may produce a more cut-resistant rope. With respect to percent strength loss, climbers can take some comfort in the finding that cutting a rope less than 20% of its diameter frequently caused no greater strength loss than ty- ing an anchor hitch to attach rope to saddle. Cordage Institute guidelines (Anonymous 2004) suggest retiring double braid and jacketed ropes for which more than 10% of the cross-sectional area of the rope and 5% of the cross-sectional area of the core fibers, respectively, have been cut. It was interesting to observe the percent strength loss in ropes due to the knot (Table 1). Texts on rope report a general degradation in rope strength of 10%–50% when a rope is knotted (Anonymous 2004; McKenna et al. 2004), although there are few data to describe the perfor- mance of specific knots (Milne and McLaren 2006). In con- trast, a spliced eye, which some climbers use on their rope, can retain 100% of the rated strength (Milne and McLaren 2006). CONCLUSIONS While this test did not simulate a specific situation in which a climber might cut his or her rope, it does reflect the general effec- tiveness of a blade to cut a rope (or a rope’s resistance to cutting). In light of the many ways a blade and rope may come into con- tact, this study was a valuable first step in investigating the acci- dent described in the earlier portions of this article. However, this study did not examine the effect of impact force, rope tension,
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