Dirty Little Secrets
The old adage “the person who steps on the rope buys beer” took on new meaning at the 2010 International Technical Rescue Symposium (ITRS) this November. We all accept that dirt reduces a rope’s strength. Presumably, grit inside a rope cuts and abrades the fibers as the rope stretches and relaxes during use. But to what degree is a dirty rope weakened? Our study presented at the ITRS examined just that, and the findings should make climbers re-examine their gear. Although the study was done with an eye toward vertical rescue, its findings are readily applicable to normal climbing. Prusik-style lengths of 8mm cord were soaked in dirty, gritty water, allowed to dry, and then put through five, 1,000-pound slow pulls to mimic realistic cord usage during rescue operations. The study found that after one soiling/pulling event, the cord had lost approximately 20 percent of its strength. After eight cycles, it lost 40 percent of its strength.
Forty percent! Many climbers use 6mm cordelettes that, when brand new, hold about 2,000 pounds. The ITRS study suggests that, when “dirty,” that same cordelette may fail at 1,200 pounds. Consider that a 165-pound climber who climbs fi ve feet off the belay and falls onto the anchor will generate about 1,800 pounds of force. An anchor that is not fully equalized in the direction of the fall may fail because of soiled cord.
How often do we take our ropes and accessory cord for granted? Do you have your cordelette hanging from a gear loop on your harness, as I do? How often do you sit on it, grinding soil into the cord? How often do you toss your climbing rope onto the dirt at the base of a climb? Black Diamond’s director of quality, Kolin Powick, tested some “well-worn” 9.4mm climbing ropes and found that sections trimmed from the ends, which get the most abuse, were failing at 1,100 to 1,300 pounds of force! (See www.blackdiamondequipment.com/en-us/journal/mountain/all/qc-labretiring- old-ropes-en-gb-en-eur.)
I urge climbers to re-examine their retirement policy when it comes to ropes, cords, and other nylon products. Dirt may be impacting these goods to a higher degree than we ever imagined. Lee Lang has been climbing for 20 years and is an active member of Larimer County Search and Rescue in Colorado, a director of the National Association for Search and Rescue, and the Wilderness SAR editor for Technical Rescue Magazine. The views presented in this article are his own and do not represent the views of these organizations.
We asked Lee Lang if washing would reduce cord damage caused by dirt. His team is currently testing this, but he thought perhaps not: “The washing may only help move the grit deeper into the core, since the soap could act as a lubricant and the grit is most likely not soluble.” Best to keep your cord out of the dirt in the first place. Other environmental rope hazards to consider:
- Water. Rope or cordage will lose up to 30 percent of its strength when wet (gaining it back when dry).
- The sun. Prolonged exposure to ultraviolet light degrades nylon. Store ropes and slings away from direct sunlight.
- Heat from friction. Nylon melts easily. Most climbers hurry to get their rope out of a sizzling-hot rappel device, but have you considered the equally hot carabiners or chains you lower off from a sport route? Rappelling instead of lowering eliminates this problem and also saves wear on anchors.
- Acid and other chemicals. Keep these away from your rope. Bleach weakens nylon, as does iodine and hydrogen peroxide, and we know of at least one confirmed incident of rope breakage due to battery acid exposure.