New techniques for safe, efficient white-water rescue.

Transcription

1 New techniques for safe, efficient white-water rescue. Matt Barker Abstract. Recent equipment failures during simulated white-water rescues have highlighted the need for detailed measurement of the loads created and the loads that can be safely sustained by the equipment currently in use for white water rescue. This research experimentally finds out; What are the potential forces involved in a white-water rescue? What forces can a three-person rescue team generate? Which of the ropes on the market are suitable for the demands of white-water rescue? Which of the current mechanical advantage rescue techniques are best suited to the equipment available? Are there any experimental techniques that could improve the force generation and safety of the rescue system? Weak points in the complete rescue system are highlighted. 1. Introduction White-water rescue equipment can be made to fail using conventional rescue practices. If failures of this type were to occur in an actual rescue environment, catastrophic results would ensue for both rescuer and rescuee. The current investigation set out to try to answer these questions, 1. Which of the ropes on the market were suitable to the demands of white-water rescue. 2. Which of the current mechanical advantage rescue techniques are best suited to the equipment available. 3. What force can a 3 man team generate 4. Are there any experimental techniques that could improve the force generation and safety of the rescue system? 2. Methods 2.1 Buoyancy aid testing On the Roberts Testing Equipment Serial number hydraulic test bed at Onehunga Chain and Rigging, the strength of the various components in the rescue harness and auxiliary clip in points of two manufacturers buoyancy aids were tested.

2 2 Matt Barker 2.2 Rope Testing The following criteria was used to select ropes for the tests, they had to have a density of less than 1 so that they floated (Polypropylene, Polyethylene and Spectra fibres have a density of less than 1), they had to be between 6 and 8mm in diameter (below 6 mm they are hard to hold and over 8mm it is hard to coil them into useable throw bags) and the materials used in construction had to be resistant to bacterial decay if left wet for extended periods. Ropes obtained were largely manufactured for use in yachting but two ropes are specially manufactured for use in aquatic rescue, PMI Water rescue and Esprit Swiftwater line. These ropes were tested on the Roberts Testing Equipment Serial number hydraulic test bed at Onehunga Chain and Rigging, when knotted and in the various 3 to 1 mechanical advantage systems. 2.3 Haul system testing A Tedea Huntleigh model no. 619 load cell was placed at the terminal end of a haul system where the forces generated by a 3 man team with a combined mass of 230kg could be measured. The haulers wore normal training shoes and stood on a flat grass surface. The variables applied were, merely pulling the rope with hands (Armstrong method), 3 to 1 pulley system, 6 to 1 pulley system, and 9 to 1 pulley system. To each of these variables were added, using or not using Petzl Ultralegere pulleys to reduce frictional losses, and pulling with hands only or attaching slings to the haul line with a marlinspike hitch and wrapping these around the haulers back so they could all pull like a tug o war anchorman. A vector pull was also tested where a 2-man team tensioned a 3 to 1 pulley system while the third locked the system off. A sling was clipped to the middle of the system at 90 degrees to the rope line and then all three pulled with their hands on the sling. 2.4 Rope abrasion tests A comparative abrasion test was devised where the ropes were dragged across a rock surface for 300km to simulate in use abrasion when hauled over rock edges and dragged around in rocky environments. 2.5 Throw bag tests The ropes were made up into throw bags to find their in use handling characteristics. They were repeatedly packed and thrown to swimmers in fast moving water. The swimmers had to grab the ropes when thrown to them and hold on while they were being hauled or pendulumed to the side of the river.

3 New techniques for safe, efficient whitewater rescue 3 3. Results Test Force at failure Type of failure Hydraulics 2004 chest strap plastic buckle 4.1kN Webbing broke Hydraulics 2007 chest strap plastic buckle 1.4KN Webbing slipped Macpac chest strap plastic buckle 1.6kN Webbing pulled through buckle Hydraulics 2004 chest strap plastic and metal buckle 6.7kN Pulled the central pin out of alloy buckle Hydraulics 2007 chest strap plastic and metal buckle 7KN Steel buckle bent and webbing slipped Macpac chest strap plastic and metal buckle 9.8kN Stitching on buckle broke Hydraulics 2004 cowstail ring 2kN Weld broke Hydraulics 2007 cowstail ring 15kN Weld broke Macpac 2005 cowstail ring 2kN Ring broke Hydraulics 2004 cowstail 2.7kN Webbing broke Macpac 2004 cowstail 6.3kN Stitching broke Hydraulics 2005 Bouyancy aid shoulder strap 4.3kN Stitching broke Hydraulics 2005 Bouyancy aid waist strap 1.5kN Fastex buckle broke Table.1. Buoyancy aid testing Table 1 shows the forces at failure for the components of the rescue harness incorporated into white water buoyancy aids as well as auxiliary attachment points that could be used to clip a person to a rope in a rescue. This testing highlighted some surprising mismatches in components and materials. Components of the same system varied in strength from 2kN to 9.8kN. The ring that attaches the cows tail to the chest strap was found to be a weak link in the both manufacturers system, failing at 2kN and the cows tail webbing and buckles used on the chest strap failed at as low as 2.7kN and 1.6kN respectively.

4 4 Matt Barker Rope Construction Fig 8 Overhand Spectralite 8mm Braided Polypropylene sheath, Spectra core 15.4kN 11.6kN Southern light Braided Spectra and Polypropylene blend 11.3kN 11.3kN Robline extreme Braided Polypropylene sheath, Spectra core 9.1kN Spectralite 6mm Braided Polypropylene sheath, Spectra core 8.5kN 7.6kN Swift waterline Braided Polyester sheath, Polypropylene core 7.1kN 7.2kN Econobraid 8mm Braided Polypropylene sheath and core 6.4kN PMI water rescue 7mm Braided Nylon sheath, Polypropylene core Robline Albatross Braided Polypropylene 4.3kN Econobraid 6mm Braided Polypropylene sheath and core 2.9kN Table.2.Terminal knot strength 5.6kN Table 2 shows the strength of the ropes using Overhand and Figure of Eight knots. The figure of eight knot with Donaghys Spectralite rope and Southern Ocean s Southern light provided the strongest terminal knots failing at 15.4kN and 11.3kN respectively. The ropes specifically manufactured as water rescue ropes, PMI s Rescue rope and Esprit s Swiftwater line, were poor performers, failing at 7.1kN and 5.6kN respectively. These ropes displayed separate sheath and core failure, probably due to the sheath and core materials not having similar stretch characteristics, therefore not loading across all fibres, leading to progressive failure at relatively low loads. Rope Marlinspike Inline 8 Clove hitch Tibloc Truckers hitch 5mm prussik Tape prussik Spectralite 8mm 15.3kN 13.4kN 13.9kN 10.7kN 10.8kN 9.4kN Southern light 9.8kN 10.7kN 8.7kN 2.3kN Robline extreme 9.1kN Spectralite 6mm 8.8kN 8.5kN Esprit Swift waterline 7.1kN 7.2kN 6.3kN Econobraid 8mm 5.3kN 7.1kN 6.6kN 6.8kN 3.5kN PMI water rescue 4.2kN 4.4kN Robline Albatross 4.3kN 4.1kN Table to 1 pulley strength Table 3 shows the force at failure for the various 3:1 pulley systems. The best performing knot used to create the 3 to 1 mechanical advantage system was a Marlinspike hitch (Pawson 2001), although the Inline fig. 8 knot and Clove hitch sometimes were stronger than the Marlinspike hitch, they tightened up to such an extent during loading that they became impossible to untie thus leaving a knot, or knot and karabiner, in the rope rendering it useless as a

5 New techniques for safe, efficient whitewater rescue 5 clean throw or rescue rope later. Prussik knots although widely used and recommended by various authors (Ferrero 1998; Walbridge and Sundmacher 1995; Ray 1997), are in fact quite inadequate to handle the maximum forces able to be applied without slippage. Fig.1 shows the force able to be applied by a 3-man rescue team. With the inclusion of small karabiner pulleys, the force able to be applied was increased by 30%. The inclusion of slings in the haul system to allow the haulers to pull with the sling round their backs rather than holding the rope in their hands only, yielded a 12% increase in force. The haulers stated that the limiting factor, when just hands were applied, was their grip on the rope and that with the sling it was much easier to create a higher force but the limiting factor then became their traction. 3 man Force Generation kn 6 4 arm strong 2 to 1 3 to 1 6 to 1 9 to Pulling with hands Pulling with slings Pulling with hands and pulleys Pulling with slings and pulleys Fig 1. 3-man force generation On the riverbank, there may well be boulders, tree roots or stumps that may allow greater forces to be applied with the sling system. The most significant increase in force was with a vector pull, using no additional equipment the force generated by our 3-man team was increased by 37%. Even more surprising is the fact that the original tensioning was achieved by a 2-man team, as one was locking the system off, so the actual increase from a 2-man 3:1 pulley to 3-man vector pull was 107%, making this a very efficient use of limited resources.

6 6 Matt Barker Rope Throwing Holding Spectralite 8mm Hard to pack into bag A bit slippery Southern light A bit light to throw packs easily Good to Hold on to Robline extreme Throws well Really slippery but didn t grate hands Spectralite 6mm Get lots in a bag Slippery and rather thin to hold Esprit Swift waterline A bit stiff to pack PMI water rescue 7mm A bit stiff to pack Slippery to hold Slippery to hold Robline Albatros OK to Throw Slippery and coarse to hold Table 4. Rope Handling Table 4 shows the results of the throw rope tests designed to test handlingproperties. There was a great variation in how the ropes were to hold, some were found to be too slippery and slid through the hands, while others with a coarse sheath were painful for the rescuee to hold onto. The worst combination was a coarse sheath of slippery material as this slipped through the hands and felt like a cheese grater as it did so. In order to pack the ropes into bags the ropes need to be soft and flexible, which the braids were but then they also needed to have sufficient weight to them to throw, which the braids lacked. The 6mm ropes were too thin for the rescuee to hold onto and ropes greater than 8mm are too bulky to get sufficient length in the bags. The abrasion tests saw the braided ropes out perform the kernmantle ropes. Of the stronger ropes, Southern Ocean s Southern light braid was a clear better performer showing little sign of wear at full distance. The Robline extreme survived the full test with its sheath intact, with the Spectralite rope s sheath failing at 30% of the distance, the Esprit rope at half distance and the PMI rope having worn through the sheath by full distance. The worst performer was the Esprit rope that was literally in tatters at the full test distance.

7 New techniques for safe, efficient whitewater rescue 7 5. Conclusions Force of Water on legs on body on boat Velocity kph Fig. 2. Drag of objects held in flowing water The force applied by moving water has an exponential relationship to the speed of flow. However the speed of water is not the only factor that rescuers have to overcome, as there is usually a large component of friction adding to the force required to free an object. Friction has a relationship to pressure and also rises exponentially, but is not calculated here, as friction is dependent on the way objects are trapped and the surface they are held against. The forces created by drag are 12kN for a swamped kayak and over 2kN for a body in water flowing at 5.3 metres per second (Bechdel and Ray 1985; Ray 1997). These figures will increase in faster flows and including variables based on friction, could lead to somewhat larger forces in actual rescues. Thoracic injury is avoided at loads of 4kN and 50% will receive injury of broken ribs on one side when well-distributed loads of 6.9kN are applied to the shoulders and chest, with a maximum survivable force of 8kN (Cavanaugh 2000). Forces required to damage the vertebrae in adults is between 6 and 8kN (Cassillo 2005). Given the above, rescue harnesses in buoyancy aids should be manufactured to withstand forces of between 6 and 8kN as a minimum as it is better to rescue someone injured than leave them to drown because the equipment failed at loads as low as 2kN as is presently the case. It is of little use to have some parts of the same rescue system built to take forces of 9.8kN when they are dependent on other components that fail at as low as 2kN. The separate

8 8 Matt Barker components should be matched in their strength rating and an overall minimum rating should be formulated for these safety items. At present some buoyancy aid rescue harnesses could potentially fail under the forces generated by even simple rescues. Haul systems need to be able to produce loads of over 10kN in order to rescue swamped kayaks in swift water (Bechdel and Ray 1985; Ray 1997). Using prussik knots to form a 3 to 1 pulley system will give you a safety valve allowing slippage before the rope breaks but will ultimately limit the forces able to be applied to any system. It is therefore counter productive to apply a mechanical advantage system greater than 3 to 1 as the prussik will likely slip at greater loadings particularly when used on slippery (Moyer, Trusting, and Harmston 2000) Spectra sheathed or blended ropes. It is recommended to use a device such as the Petzl Tibloc to create a mechanical advantage haul system where it is necessary to have a traveling attachment point on the main haul line as this produces a stronger and more consistent traveling attachment point. The strongest haul systems were created using Spectra cored Polypropylene sheathed or Polypropylene and Spectra mixed braids of 8mm diameter using a Marlinspike hitch and karabiner pulleys wherever the rope ran round a karabiner. Indeed the reduction in friction with the addition of plastic karabiner pulleys added the equivalent of an extra person to a 3-man team making them well worth their 10 gram weight. Pulling using slings attached to the main haul line also creates a useful boost to peak force generation and may be even better in places where there is better traction. Ropes for aquatic rescue should be manufactured containing a significant proportion of floating fibres (Spectra, polypropylene and polyethylene). The ropes core and sheath should have similar elongation characteristics, so that the sheath and core share loads and are therefore stronger per cross sectional area than ropes where the core and sheath behave differently. Ropes of a braided design stood up to abrasion much better but where kernmantle designs are used the sheath should be relatively thick so as to remain integral after in-use abrasion. These ropes should be manufactured with a target knotted tensile strength in excess of 10kN in 8mm diameter form, to be aligned with the strength of attachment points on kayaks, the maximal survivable loads through chest harnesses and the likely forces required in rescue of swamped kayaks.

9 New techniques for safe, efficient whitewater rescue 9 6. Acknowledgments I would like to thank the following for their help in getting this research from the ideas stage to completion. Institute of Sport and Recreation Research New Zealand (Auckland University of Technology) for grant aid. Hydraulics (New Zealand) for supply of buoyancy aids and materials. Donaghys Ropes (Australia) for supply of ropes. Southern Ocean Ropes (New Zealand) for supply of ropes. Onehunga Chain and Rigging, Auckland, for use of their test bed. References Bechdel, L. and Ray, S. (1985)River Rescue. Appalachian Mountain Club Boston Cassillo, F. (2005) Kinesiological and Anatomical approach to the Deadlift. Retrieved 14/10/2005 from Cavanaugh, J. (2000) The Biomechanics of thoracic trauma. BME 7160, Winter Retrieved 14/10/2005 from Ferrero, F. (1998) White Water Safety and Rescue. Pesda Press, Wales Hopkins, R. (2003) Knots. Thunder bay Press, San Diego Moyer, T., Trusting,P. and Harmston,C. (2000) Comparative Testing of High Strength Cord. Paper presented at 2000 International Technical Rescue Symposium Pawson, D. (2001) Pocket guide to knots and splices. PRC publishing, London Ray, S. (1997) Swiftwater rescue. CFS Press, Ashville NC. Walbridge, C. and Sundmacher, W.A. (1995) Whitewater rescue manual. Ragged Mountain Press, Camden ME.