128 Kane et al.: Impact Force and Rope Tension Arboriculture & Urban Forestry 2010. 36(3): 128–131 Impact Force and Rope Tension Affect Likelihood of Cutting a Climbing Rope with a Handsaw Brian Kane, Mollie Freilicher, Mac Cloyes, and H. Dennis Ryan Abstract. A previous study has demonstrated the ease with which a climber could cut his or her rope using a handsaw (Kane et al. 2009). In a previ- ously published effort, however, the authors did not examine the effect of two variables that presumably influence the ease with which a rope can be cut: rope tension and impact force of the blade. In the current study, two types of rope are cut using one type of blade, with varied rope tension (seven levels) and impact force (four levels) of the pendulum-mounted blade on the rope. Increases in impact force and rope tension increased the ease of cutting both ropes tested, but impact force was the dominant effect. At the greatest impact force, which was similar to the impact force a climber could exert using two hands on a handsaw, all but one rope was completely severed. The results are discussed in the context of climber safety. Key Words. Handsaw; Rope. A previous paper documented the ease with which a climber could cut through his or her rope with a handsaw (Kane et al. 2009). In the in- terest of quickly publishing those results to increase awareness of the inherent danger, the effect of two presumably important variables— rope tension and impact force (or velocity) of the blade—were not in- vestigated. The impetus for this line of investigation was an accident, where a climber cut himself out of a tree using his handsaw, result- ing in a fall that broke his neck (Georgia Arborist Association 2009). There are many ways a climber’s handsaw (or pole saw) might contact the lanyard or climbing line. The impact force of the blade on the rope and rope tension can both vary dramatically. For ex- ample, climbing on a static system, such as when ascending the tree using the single rope technique, a climber’s full weight is on the climbing line. In contrast, when using a dynamic climbing system, which is typically how climbers work once secured in the tree, a climber’s weight is supported roughly equally by the two legs of rope attached to his or her saddle. Dynamic loading of the rope, such as when a climber swings (intentionally or by accident), will increase rope tension. In other cases, when a climber is stand- ing on a branch or on spikes, secured to the trunk with a lanyard, the tension in the lanyard will be less than the climber’s weight. With respect to the impact force of a saw on the rope, a climb- er could exert full force with two hands on the saw and finish cut- ting a branch sooner than expected, hitting the rope. In contrast, the saw might unintentionally contact the rope as the climber puts the saw back in its scabbard. The objective of this study was to quantify the effects of rope tension and impact force of the blade on the likelihood of cutting one’s climbing rope with a handsaw. METHODS AND MATERIALS Ropes and blades were tested as previously described (Kane et al. 2009), which included hanging a 2.13 m section of rope ©2010 International Society of Arboriculture from a beam and swinging a pendulum-mounted saw blade (Fig- ure 1) into the rope under tension. For the current investigation, one type of blade was used (alternating between five individu- als), Silky Zubat, and two types of rope [Poison Ivy (24-strand construction, 11.7 mm nominal diameter) and XTC (16-strand construction, 12.7 mm nominal diameter), both manufactured by Yale Cordage, Saco, ME]. The authors chose Zubat because the handsaw completely severed each previously tested rope (Kane et al. 2009). Ropes were chosen mostly out of convenience, as un- used rope of both types remained after the previous investigation (Kane et al. 2009). The choice also reflected a desire to test ropes of constructions and diameters commonly used by climbers. The authors tested ropes in a randomized complete block de- sign, blocking rope tension (111, 156, 200, 267, 311, 356, 400 N) within each height of swing of the pendulum (quarter, half, three- quarters, and full, which corresponded to impact forces of 143, 267, 509, 731 N), and repeating each rope by swing by tension test three or five times. To save rope, if a particular rope was cut completely through on the first three tests of any swing by tension combination, the last two tests were not conducted. Measure- ments of rope diameter were taken under tension before and after testing, calculating the percent difference as the response variable (percent cut). The impact force measured when the second and third authors pulled on a handsaw handle attached to a load cell (n = 20) ranged from 267 N (one-handed) to 738 N (two-handed). The authors used a three-way analysis of variance (ANOVA) to investigate the effects of the type of rope, rope tension, im- pact force, and their interactions, on percent cut. To separate sig- nificant (p < 0.01) means, orthogonal polynomial comparisons were used. The ‘contrast’ statement in the GLM procedure in SAS (ver. 9.1, Cary, NC) was used within significant main ef- fects. For significant interactions, the ‘slice’ statement in the GLM procedure was used to investigate differences between
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