Ropes may be considered an arborist’s most important tools. They can be used to support limbs, tools or a person. Their adequacy as a tool is based on material, construction, tensile strength, elasticity and working-load limit. Manufacturing techniques, including the way rope strands and yarns are twisted and braided, also affect the characteristics and durability of various types of rope. Because of its role in supporting tree climbers or heavy limbs in rigging operations, it is of utmost importance to purchase ropes that are approved for tree work. Arborists shall maintain their ropes in proper working order and retire them once they show signs of excessive wear.
Common factors that weaken rope
Shock loading — This is a dynamic, sudden force placed on a rope or rigging apparatus when a moving load or piece is stopped. Shock loading can occur during rigging operations when a piece of wood falls and is then caught suddenly by a rigging system. The farther a piece falls before being caught by the system the greater the amount of force generated and experienced by the rope, rigging point and rigging system. Letting a piece run and bringing it to a stop more slowly will put less force on the rigging system and rope.
Sharp edges — Sharp edges can cut or cause heavy abrasion to a rope. These edges may appear naturally on a tree and affect a rope when you are using a natural branch union. Be aware of any sharp metal pieces embedded in trees that might cut a rope under tension. Sharp edges may also be present on climbing hardware or other equipment, meaning that proper inspection before each use is critical.
Stretch — Any time a load is placed on a rope stretch can occur. The rope may bend or get caught when a portion bears the majority of the load unevenly. This is due to forces resulting from the load not being able to flow or travel well beyond a bend in the rope. Depending on the bend, the part of the rope from the bend to the load may bear almost all of the force, and the part of the rope from the bend and away from the load may bear almost none of the force. This is considered an unequal load.
Friction — Friction occurs when a rope rubs against itself, another rope, hardware or a part of the tree. The rubbing causes wear on the rope, which decreases its strength over time. Using devices like blocks, pulleys, and ring friction savers correctly can help protect a rope from wear and extend its service life. Ropes that have a mantle sheath with larger strands generally have a higher resistance to abrasion.
Heat — Excessive heat is a natural enemy of most materials, and rope is no exception. Arborist ropes are subjected to a lot of heat. Friction causes heat when rope rubs against blocks, equipment, rigging points, tree limbs and other objects. Rope rubbing against rope also causes hot spots. Heat is a factor in reducing a rope’s service life. It’s important to take measures to avoid excessive friction or conditions that may produce excessive heat on your rope.
Moisture — This can cause strength loss in ropes depending on the material they’re constructed from. While nylon has some absorption properties and can lose strength when wet, a material like polyester does not experience strength loss due to moisture. This is one reason why most arborist ropes are constructed from polyester. It’s recommended that you store all of your ropes in a rope bag to keep them clean and dry. Do not use excessive heat to dry your ropes, and do not store them on the ground.
Knots — Each time a knot is tied in a rope it loses a percentage of its original strength.
Signs of a weak rope
Regular rope inspection shall be performed before each use to determine if the rope is still in proper working condition. During inspection, look for the following characteristics of a weak rope:
Discoloration — This may be an indication of chemical damage.
Variance in diameter — Variance in diameter may indicate core damage.
Hard spots and contamination — These usually signify a rope is excessively worn or weakened by overloading and shock loading.
Gloss, glaze and streaks — These indicate signs of heat or friction damage.
Frays, pulls and broken strands — If more than half of the outer sheath is frayed, then you should retire the rope immediately. Broken strands may indicate the rope was torn by friction, cut by a sharp edge, or the working-load limit was exceeded. Retire the rope immediately if two or more strands are broken.
Heavy abrasion — Usually caused by friction and extreme wear.
Milking — This is the shifting of the sheath leaving a rope end without a core.
- Here are some simple things you can do to increase the service life of a rope and limit damage:
- Hang your rope off the ground or keep it in a rope bag. A rope can absorb chemicals from concrete or other porous surfaces when kept on the ground.
- Use a rope washer or wash your rope in a washing machine on a delicate cycle to clean off dirt and grit. Do not use detergents or fabric softeners, and do not put the rope in a dryer. Ropes should be hung to dry.
- Try to use the rope on smooth, natural branch union points or use a friction-reducing device to help maintain the rope’s original strength and lessen abrasion.
- Keep the rope away from temperatures that can cause rope damage.
- Cut off damaged portions of the rope and rotate the use of climbing line ends if not using a spliced eye.
Monitor rope use
Monitoring the use of a rope will help you assess its condition and strength during daily inspections. Avoid using a rope that has been loaded above the working-load limit. Remember that the tensile strength decreases after each use of the rope. After purchasing a rope, write down:
- the date the rope is put into service;
- rope tensile strength;
- the working-load limit;
- its type of use; and
- the approximate latest date the rope should be retired.
Once a rope is ready to be retired from climbing or rigging applications, it can still be used as a tag line. When disposing of an old rope, it’s best to cut the rope into short lengths to prevent someone else from using it.
Remember these key points about rope safety:
- Always visually and manually inspect ropes before each use and remove from service ropes that show signs of excessive wear or damage.
- Always keep loads under the working-load limit.
- All climbing gear, including lanyards, hardware, saddles and splices, must be in good working condition and not be altered in a way that would compromise the integrity of the equipment.
- Rope should be clearly marked for specific use (i.e., which ropes are for climbing and which ropes are for rigging).
- Never leave a rope unattended in a tree.
- Review rope regulations and standards governing your region (in the U.S., refer to ANSI Z 133-2012 Safety Requirements for Arboricultural Operations section 8.1).
Carefully monitoring rope use, selecting the right ropes for the specific purpose, adhering to safety standards, and properly maintaining and storing your ropes and other equipment will help ensure a safe and efficient worksite.
To learn more about rope construction, maintenance and selection — and earn CEUs — visit ISA’s Online Learning Center to take the new course, Arborist Ropes.