Rope Rescue Course
Last week, I had an opportunity to attend a Technical Rope Rescue Course through Raven Rescue. This was an eight day course designed mainly for firefighters and search & rescue personnels. It covered rope rescues on low angle slopes, high angle cliffs and highlines over a canyon where you rig a line across and get lowered (Tyrolean). Since this wasn’t designed for climbers, I thought skills I learn in this course would be a good knowledge, not necessarily skills for climbing but I learned so many things I can apply to climbing.
Rescue equipments are different from climbing gears. As I expected, everything was much bigger compare to climbing gears. Most gears for rescue are G-rated, which means they are rated for multi-personal use. G-rated gear must be used in systems hauling more than one person, such as multiple rescuers or a rescuer and a patient. Climbing carabiner can be used as long as it only will be loaded with single person. Just to give some ideas how strong G-rated gears are, a G-rated carabiner is rated for at least 40kN and a regular climbing carabiner’s minimum strength is 20kN. G-rated 12mm static ropes we used are rated 40kN, regular climbing single dynamic ropes are rated about 8-10kN. Dealing with 12mm static ropes weren’t my favorite part of training, but it was fun to use gears that were new to me. Some of the gears that we used were I’D which is like a bigger Grigri and MPD which is an auto-locking lowering & raising device with a pulley inside.
We also learned how to use non-autolocking devices such as Scarab and Brake Rack.
In this course, I learned that one of the common anchors in climbing was not a recommended anchor. It’s girth hitch. Here’s the reasons why: it creates a friction point on nylon on nylon and also the angle of the anchor is too wide that it’s not as strong as it can be.
I have been using girth hitch on a tree belay on single pitch or multi pitch climbs. Most climbing falls don’t generate enough force for girth hitch anchor to fail, but instructor had a point. Catching a dynamic fall on girth hitch can cause frictions on nylon on nylon and potentially melt sling/webbing on the hitch. If I was belaying a lead climber on a tree belay on multi pitch, or even belaying a second climber from top, if there was a traverse the anchor can have a dynamic load. We also know not to build an anchor with too wide angles, but it never crossed my mind on girth hitch. When my instructor asked me what was the angle on girth hitch, I said “0 degree?” It is 0 degree on webbings from the hitch, but the actual angle is the one that comes to the hitch on a tree which can be quite wide. Wide angle weakens an anchor significantly.
Here’s an example with 1000 lbs of load.
At 20 degree, each anchor point gets 500 lbs of load. At 120 degree, each anchor point gets 1000 lbs of load. Anchors with wider angles increases loads put on each anchor point. Most likely, a tree can hold a climber’s fall but why wouldn’t I reduce the force if I can with a different anchor which is as easy to build as a girth hitch? In rescue operations, basket hitch is one of the popular anchors. You can reduce the angle of the anchor significantly with the right length sling.
Sometimes, an anchor tree is too big that a sling barely wraps around a tree. This can create tri-loading (three directional pull) on a carabiner which weakens the carabiner strength. If you have a longer sling or corderette, you should replace it, or you can add a carabiner to the system to fix tri-loading.
Since hauling is a huge part of rescues, we practiced a lot on hauling systems with pulleys using Mechanical Advantages. Not having done any big wall aid climbing or cravasse rescue, pulley systems were new to me. Having pulleys and prusiks in a hauling system can multiply the efficiency. Here is an example with 9:1.
9:1 means 1 person pulling a rope can generate 9 people worth of pulling strength. When we count, we start from a person pulling the rope (the instructor in gray jacket is not putting any force, he was showing us how to build this system). One person pulling red rope generates pulling force of 1, multiplied by 2 at first pulley (1 incoming rope and 1 outgoing rope), the force of 2 travel down the first prusik. The Force of 1 person pulling the red rope keeps traveling down on the rope and meets the force of 2 at the first prusik, becomes force of 3 (1+2=3). The force of 3 gets multiplied by 2 at the second pulley (same thing, 1 incoming rope and 1 outgoing rope) becomes 6 and travel down the second prusik. The force of 3 on red rope keeps traveling down and meets force of 6 at second prusik and becomes 9 (3+6=9). As a general rule, we shouldn’t exceed 12:1 ratio in rescue. If 12:1 ratio is exceeded, it will put too much force on equipments, causing them to break. Adding more people to pull would multiply the force. For example, if you build a system with 3:1, 4 people are the maximum number of people who can pull the rope (3×4=12). This is an example of Simple Mechanical Advantage. There’re three kinds of Mechanical Advantages (Simple, Compound, and Complex), but I’m not going to explain the difference here. Simple Mechanical Advantage is confusing enough. 🙂