WSCMRT Training - Basic Ropes and Knots
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WSCMRT Training - Basic Ropes and Knots One of the most basic and important tools we use is rope. This is our lifeline and it enables us to extend our rescue operations into just about anywhere. To do this job safely and well we must be intimately familiar with this tool - its strengths and limitations as well as its proper care. Quite literally, your life depends on it. Types of Rope There are a number of different ropes available. They can be made of: * Nylon - strong, flexible, resists abrasion, reasonable price - the top choice for rescue operations. * Kevlar - very strong, stiff, subject to heat and sharp bends - used in some rescue applications. * Polypropylene - low strength & durability, floats - sometimes used for water rescue. * Polyester - low stretch, takes shock loads poorly - not used for climbing or rescue. * Manila (hemp) - weak, deteriorates rapidly - not acceptable for climbing or rescue. Ropes are also classified based on how they are constructed. * Laid rope - traditional 3 strand construction with the strands twisted around each other. The load bearing fibers are exposed to the outside and more susceptible to damage. Often stiff. * Kernmantle - a 2 part rope made of long strands in the middle Figure 5-1: Three strand twisted (the kern or core which carries 70 to 90 % or the load) and or laid rope. a woven exterior that protects the core (the mantle). This is by far the most common style used in rescue applications. * Double Braid - like a kernmantle but the strands in the inner core are also woven or braided together Figure 52: Static, kernmantle rope showing core (kern) and sheath (mantle). * Tubular Webbing - a flat tube of woven nylon in widths of l/2” to 3 inches. One inch tubular webbing is our most common form. Elongation refers to how much a rope stretches when a 200 lb. load Figure 53: Dynamic, kernmantle rope used for and a breaking load is placed on it. Static rope stretches about 2% with a 200 lb. load and 20% with a breaking load. This low stretch is desirable for most rescue uses. Dynamic rope stretches 6 to 9% with 200 lbs. and 40 to 60% with a Figure 54: Double braid rope showing tbe braided breaking load. This absorbs the energy of a falling load so dynamic sheath and braided core. ropes are commonly used for sport climbing but not much in rescue. Knotabilitv refers to how stiff a rope is. A soft and flexible rope is easy to tie and tighten knots in but when loaded it may be very hard to untie the knots. A stiff rope is hard to manage, difficult to tie and tighten knots and knots come undone easier. For rescue applications we prefer the middle of the spectrum - relatively easy to tie but unlikely to come undone and relatively easy to untie. Tensile Strength or Breaking Strength of a rope refers to how much weight will it take to break a straight length of a rope or other piece of equipment. This is a very importantnumber to be familiar with for all of the tools we use. Knots and ropes going over sharp edges or bends reduce the actual breaking strength of a rope significantly. Below are approximate breaking strengths of the ropes we use regularly. Get to know them by heart. 7mm kernmantle (used for prussiks) 2500 lbs. 7/16” (llmm) static kernmantle rescue rope 6,000 to 6,500 Ibs. 7/16” (llmm) static laid rope 6,000 lbs. l/2” (12.5mm) static kernmantle rescue rope 8,000 lbs. 1 inch tubular webbing 4,000 to 4,500 lbs. Recommended Working Load is usually considered to be 8 to 11% of the tensile strength of laid rope and 15 to 20% of the tensile strength for kernmantle rope. Our rescue loads are usually within the 400 to 1000 lb. range so we are within the working load limit of our equipment. Another way to think of it is to make sure the system you set up has a 4 to 1 safety ratio between your load and your tensile strength. In order to stay within these limits it is important to avoid shock loading our systems as much as possible Shock Loading occurs when your load falls free for a distance before it is stopped by the rope. The farther the load falls the greater the force exerted on your rope. Gravity never sleeps. See the table below and note how the force increases with the length of the fall for a 500 lb. load. Length of Fall Fall Speed Fall Energv (ft./lbs.) for 500 lb weight 3 ft. 10 mph 500 6 ft. 14 mph 1000 . 15 ft. 23 mph 2500 30 ft. 32 mph 5000 You get the idea. The lesson is that we need to avoid shock loading as much as possible. If you have to shock load be sure to keep it short, Appropriate Care and Handling of Rope Many factors degrade the integrity of a rope. Since good ropes are expensive and because your life depends on it you must do your best to take good care of rescue rope. * Do not step on a rope. This grinds sand and grit into the rope that cuts the fibers. * When setting up your systems use edge rollers or padding to avoid sharp edges & abrasion. * Avoid letting rocks fall on the rope. One careless rock can destroy a $200 rope. * Don’t let one rope slide over another - heat from friction can cut a rope quickly. * Try not to drag ropes through dirt, mud, water or snow if you can help it, * Keep ropes away from gasoline, oil and other chemicals. * Avoid long term exposure to the sun’s ultraviolet rays. If you cause a rope to be damaged be sure you let the safety officer know immediately so they can evaluate whether it needs to be replaced. The same is true if you notice damage to a rope such as a frayed mantle. Isolate such spots by tying them into the middle of a knot, The use each rope receives on trainings or missions must be recorded on individual rope cards which notes how much tension and abrasion the rope suffered. Ropes are kept in individual bags. They must be dried out before they are put away or they will mold. They must be washed periodically with water and a special rope washing tool. Ropes are usually retired after about 5 years of gentle use. Knots‘ . Knots . allow. us to expana tne use or our ropes With them we can make loops to tie into, join two ropes together, create braking, holding and safety structures and much more. To realize these benefits you need to know which knot to use when and how to tie it properly. You need to become familiar enough with the knots to tie them with gloves on, in the dark, during a snow- storm. That means lots of practice and periodic review so you don’t forget. The bends that a knot makes in a rope has the effect of reducing its strength. Some knots reduce strength more than others. We try to choose the strongest knots that will do the job we need. The list at right will give you an idea of the C n approximate strength reductions caused by common knots. Basic Knots and Their Use Figure 8 Follow Through - this is a strong knot used to tie a rope around something e.g. a litter. Make a simple figure 8 down on your rope. Run the end of your rope around the thing you are tying into. Then thread the end of the rope backward through your figure 8 following each bend until you come out the far side. common knot for putting a loop in the Finish with a safety backup. end of a rope because it is strong and easy to untie. Be sure to dress the knot to remove any twists. If you have a short end, finish it off with a safety backup (half of a double fisherman’s knot). You load line should be on top of the knot. Double Sheet Bend - this is our preferred knot for tying 2 ropes together because it is easy to untie after being tensioned; Both sides of the knot must have a safety backup. Three Wrap Prusik Prussik Knot - this is a very important knot because it allows us to tie a move- able anchor on to the rope. It is often used as a backup safety during a rappel. Two of them set in tandem are used to grab or hold the rope for rescue loads e.g. in uphaul systems. Be sure . the knot is neatly dressed as shown. Double Fisherman’s Knot or Grapevine - A great knot for tying 2 ropes together as long as you never need to untie it. We usually use it to tie up prussiks. Be sure your finished knot looks like the picture. No Knot (Tensionless Anchor) - this is a preferred method for-tying in to a tree. This retains the full strength of the rope. The friction of the rope around the tree is what makes it hold. Be sure to use 4 wraps around the tree. The knot and biner should not be under tension. Water Knot - this is the best knot to join flat webbing. Start with a simple overhand knot then thread the other end back through in the opposite direction. b Be sure you have at least 2 inches of tail on each side of the knot. Also be sure to tension the knot before you use it or it may come undone.