Author(s):
Dan Lack - Rocky Mountain Rescue Group
For the Rocky Mountain Rescue Group (RMRG), based in Boulder, Colorado, rescuer and patient safety is paramount. The 70-person, all-volunteer rescue group is the oldest mountain rescue team in Colorado. RMRG has been rescuing people throughout the Colorado mountains for 60 years and, in that time, has become a leader in the development and testing of specialized equipment and innovative mountain search and rescue techniques.
Equipment manufacturers usually test their equipment by applying loads quasi-statically; however, a drop, not applied loading, is the most likely cause of equipment failure during a rescue. For this reason, we regularly test rope elongation, failure strength, and recovery, as well as load limiters such as shock absorbers, at our testing facility in Boulder.
Testing New Safety Equipment
In 2000, RMRG retrofitted the upper 10-meter section of its high-tension power-line tower. A remotely operated winch on the testing tower can lift loads of up to 450 kg, with remote release for drop tests. We use load cells to measure up to 45 kN of force; high-speed in-line amplifiers condition the output of the load cells and provide analog signals to a National Instruments DAQCard-1200 in a laptop running NI LabVIEW. Two of the four analog input channels may be used to measure temperature changes, load position, or the position of other moving points in the system.
With LabVIEW, we can program our software application and include the functionality we want. As volunteers come and go, new people can take up the testing reigns without needing to rewrite software or dig into specialized code.
We recently tested Mamutec’s Paraloc™ rope to determine its efficacy in mountain rescue. RMRG members Jim Gallo and Bill May conducted drop tests to evaluate the ultimate strength of the rescue rope. A typical test involves dropping a 280 kg weight on a length of rope with knots to simulate a severe rescue situation. The position of the weight during the drop and settling of the knots, from tight to loaded, was recorded. Distances were measured using traditional linear translation transducers known as “string pots,” which convert a one-meter change in position to a 3.3 V change in signal level.
By conducting these high-speed tests, we can assess the quality of the rope and whether we need to include shock absorbers in the rescue rigging. One example of a shock absorber is the prussic knot, which slipped at 11 kN on the first drop. In these extreme conditions, the prussic knot limited the load but fused to the rope, effectively welding the system. We did find, however, that the Paraloc rope could withstand at least two more drops than our previous rope.
We also tested elongation, a property that can both help and hinder rescue operations. Too much elongation of a rope under load introduces undesirable stretch when long lengths of rope are used on vertical walls or steep slopes. Too little elongation does not provide any shock absorption, increasing the possibility for shock loads that cause catastrophic failure.
Future Development
RMRG, with the help of National Instruments, is expanding its testing capabilities and hardware. With the National Instruments USB-6251 M Series multifunction data acquisition (DAQ) module and LabVIEW, RMRG plans to add more advanced testing methods for greatly improved measurement results. No organization has published fundamental, quantitative high-speed or dynamic rescue rope properties, including elongation, and rope manufacturers do not provide this information. With LabVIEW and high-speed DAQ hardware from NI, RMRG is now in a position to acquire and analyze data from optical encoders and other sensors to provide dynamic rope properties, leading to significantly better understanding of rescue systems.
Because we acquire data to a laptop, a USB DAQ solution also can improve the portability and security of the acquisition equipment, compared to a PCI option. Additionally, it provides cost savings, which is a significant benefit for a nonprofit organization.
Ensuring the Safety of Rescue Teams and Patients
As a mountain rescue team, it is essential that we understand rescue loads and the behavior of our rescue equipment – especially ropes, knots, carabiners, anchor materials, and descending devices – under these loads. For decades, RMRG has been recognized nationwide for its development and testing of mountain rescue techniques and equipment, and we continue this development for the benefit of those who get into trouble in the mountains and those who go to save them.
For more information, contact:
Rocky Mountain Rescue Group
P.O. Box Y
Boulder, Colorado
(303) 449-4141
contact@RockyMountainRescue.org
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