180 Brian Kane: Compatibility of Toothed Ascenders with Arborist Climbing Ropes Arboriculture & Urban Forestry 2011. 37(4): 180–185 Compatibility of Toothed Ascenders with Arborist Climbing Ropes Brian Kane Abstract. Climbers are increasingly using ascenders to access trees, both as a substitute for Prusik loops used in footlocking a doubled rope and with the single rope technique. Manufacturers, however, have explicit limitations on use of ascenders, many of which are violated when used in tree climb- ing. Ascenders were tested on four arborist climbing ropes in a dynamic drop test; impact load and arrest distance were measured. Of 67 tests, arrest distance met the EN 12841-2006 Standard (≤2 m) only 10 times. Impact loads averaged more than five kN, adding a backup friction hitch to the as- cender increased impact load to more than six kN. Climbers need to be made aware of the appropriate use of ascenders, and only use compatible ropes. Key Words. Ascender; Climbing; Rope. A characterization of the rope-ascender interaction is nec- essary to validate the adoption of ascender use by arbor- ists. In recent years, climbers have incorporated mechani- cal ascenders into their ascension and climbing systems, as described in popular literature (Jepson 1995; Bridge and Cowell 2009; Clark 2009). Although ascenders are manu- factured in accordance with rigorous United States [NFPA 1983-2006 (Anonymous 2006c)] and international [EN 12841-2006 (Anonymous 2006b); BS 567-1997 (Anony- mous 1997)] standards, such standards do not guarantee that ascenders designed for use in other disciplines are compat- ible with typical arborists’ tree climbing gear and practices. Climbers use ascenders in various ascension systems, including as a substitute for a Prusik knot while static foot- locking a doubled rope and with the single rope technique (Jepson 1995; Dunlap 2002; Bridge and Cowell 2009). Al- though replacing Prusiks with ascenders may facilitate ascent into trees and provide many perceived advantages, empirical testing has not yet confirmed them. While the use of ascend- ers in ascension systems may provide advantages, their use is clearly limited by manufacturers, and it is imperative that climbers understand the limitations of any piece of gear. As- cenders come with explicit warnings in product literature to address limitations, such as the appropriate construction and diameter of rope to use with ascenders. Product literature also warns that a) climbers who use ascenders [which are typi- cally classified as Type B rope grabs by the EN 12841-2006 Standard (Anonymous 2006b)] on a working line, must also be secured by a safety line with a Type A rope grab; and b) climbers must avoid substantial falls that would cause an im- pact load (Petzl 2010). Popular arboricultural literature of- fers similar cautions. Common safety recommendations in- clude: backing up ascenders with a friction hitch above the ascender (Blair 1995; Jepson 1995; Tresselt 2006), keeping the cam of the ascender clear of debris (Jepson 2000; Dun- ©2011 International Society of Arboriculture lap 2002; Bridge and Cowell 2009), and avoiding dynamic loads and loads of more than a single person (Blair 1995). Testing of ascenders by manufacturers has demon- strated that a toothed ascender will cut the sheath of a 13 mm diameter kernmantle rope at 6.5 kN (Petzl 2010). Bridge and Cowell (2009) presented similar anecdotal evidence, suggesting that manufacturers’ recommenda- tions are relevant to the arboricultural use of ascenders. Despite warnings to use ascenders in accordance with manu- facturers’ recommendations and accepted standards, question- able use of ascenders occurs in arboriculture. At the Internation- al Tree Climbing Championship, many competitors creatively use ascenders in the aerial rescue event, but many such uses are forbidden by manufacturers (E. Carpenter, pers. comm.). Replacement of Prusik loops with ascenders, which creates the potential for a significant fall and impact loading not recom- mended for use with ascenders (Petzl 2010), is another example of inappropriate use of ascenders in tree climbing. Such use, however, is often depicted in popular arboricultural literature. For example, ascenders shown in Tresselt (2006) are used in conjunction with a lanyard (backed up by a French Prusik) as a substitute for a traditional footlock Prusik. This particu- lar climbing system allows a fall of the length of the lanyard, generating a substantial impact load on the ascender and rope. If a climber were simultaneously secured with a Type A rope grab to a safety line, the risk to the climber would be reduced, but arboricultural ascension and climbing systems infrequent- ly incorporate a safety line. Images in Clark (2009) show as- cenders in use on Safety Blue Hi-Vee and XTC-Plus, neither of which is a kernmantle rope as defined by the EN 1891- 1998 Standard (Anonymous 1998) and required by product literature (Petzl 2010). It is not the author’s intent to dismiss the value of popular literature in presenting potentially help- ful innovations in climbing systems. Such articles are based on years of experience and admonish climbers to incorporate in-
July 2011
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