Q: What is kernmantle rope?
A: Kernmantle rope that consist of an inner core (typically nylon) fibers. This inner core is contained by an outer braided sheath made out of nylon and/or polyester. Some rope that is designed for high heat or aggressive edge environments will have an outer sheath braided with combinations of aramid fibers such as Technora.
Q: What is the difference between static, low-stretch, and Dynamic rope?
A: All of these terms are usually associated with some form of kernmantle rope. These adjectives all define the amount of elongation, (stretch) of these standardized categories. Elongation of rope is high calculated and is a direct result of the core materials and methods of the manufacturing process. In general, static rope may stretch up to 6% when pulled to 10% of the MBS (minimum breaking strength). Low stretch rope may stretch between 6% and 10% at 10% of the MBS. Dynamic rope is generally considered to be sport climbing rope and is usually graded by the number of falls. Given a 80kg load, the first UIAA test fall must be less than 40% elongation, and the static elongation test of dynamic rope must not exceed 10% for a single rope (quoting Beal Ropes).
Q: What is the difference between polyester, nylon, and aramid rope construction?
A: All rope manufacturers use various blends of fibers (usually polyester and/or nylon) to spin their various rope products. These rope recipes are strictly guarded trade secrets. Polyester offers less stretch than nylon and it has more water-resistive qualities. Nylon is said to be to be somewhat less likely to break due to more elasticity qualities. Predominantly polyester designed static rope has minimal stretch. This can be extremely useful for high tension applications such as highline rigging, however, due to the low elongation caution should be taken with conventional rescue belay systems. In such scenarios manufactured energy absorbers may be employed.
Aramid fibers such as Technora, and Kevlar are much more heat resistive. The maximum working temperature of nylon and polyester blends is around 250o F. Technora rope working temperature is about 350o F with a decomposition temperature of about 900o F. Technora rope is a common rope used for firefighter bailout kits, and specialized high heat industries such as steel mills.
Q: Which rope diameter is better for rescue, ½ inch or 7/16 inch?
A: ½ inch (12.7mm) rope has been pretty much the mainstay in the US fire service for the past few decades. It is also widely used by industrial rescue teams. Due to the thickness of ½ inch rope there is a growing view by many seasoned rope access and rescue practitioners of it having a fat feel and lacking the handle (or knotability) that is found with 7/16 (11mm) when the job requires more advanced rope access rigging and knot work. In terms of rope strength, the quality of today’s cordage manufacturing industry, combined with the increased awareness of true safety margins and rigging physics, a 10:1 safety margin is quite obtainable with a two person rescue load when using 7/16 rope. For those rescue teams that are not totally comfortable with technician level rigging skills the ½ inch rope may offer a little more comfort in meeting their basic rescue needs.
Some important factors in choosing ½ inch or 7/16 inch rope are:
- The existing team hardware cache: Many descenders, rope grabs, and belay/fall arrest devices are dependent on the diameter of the rope. To completely change over from ½” to 7/16” could require the expensive purchase of compatible 7/16” hardware.
- The nature and severity of the vertical environment: 7/16” rope and the required accompanying hardware is a must have requirement for any rope access job, including, vertical structural steel environments such as towers, wind turbines, and bridges. Much of this is due simply to the weight of the rope during an extensive climb. Additionally many 7/16” descenders are much more user friendly when performing changeovers from descending to ascending and back again.
- Comfort level: Teams that are asked to perform basic rescues such as non-entry confined space rescues, and horizontal confined space entries typically use ½” rope. They feel comfortable with this diameter and it easily meets their less frequent rescue needs that presents a much less aggressive vertical challenge.
Q: Should a lightly-used rope (that passes visual inspection) be retired once it reaches a certain age?
A: Section 5.2.2 of ASTM F1740-96 (2007) Guide for Inspection of Nylon, Polyester, or Nylon/Polyester Blend, or Both Kernmantle Rope recommends 10 years as a maximum rope life.
Our rope that still looks like it is in great shape tends to stay in our equipment cache as long as possible. However, visual inspection can be very subjective to the individual who is doing the inspecting. It is important to remember that rope is a textile. Like all textile products, rope will wear over time and use. Visual inspection of a rope will identify wear issues to the sheath, whereas the only way to inspect the core (which is about 85% of the rope strength) is through feel. We can feel major soft spots that may indicate core separation, but we cannot identify micro damage to the core fibers due to years of tying and untying knots, and rigging through pulley systems and friction devices. It is this decomposition of the core over a long period of time that presents unknown condition factors during rope inspections.
A key requirement of all rope manufacturers is diligent maintenance of rope records. The only defendable way to classify if a seasoned rope has had only light use is through the reference of its documented history.
Q: Is there a rope manufactured that is arc-flash rated and/or di-electric rated?
A: Yes on both accounts. However, it is important to understand that arc-flash ratings and di-electric ratings are two very different assessments.
With arc-flash we think of a very quick and extremely hot event such as a circuit box explosion or live electrical lines grounding out. Required PPE is heavily regulated by OSHA 1910.335 and NFPA 70E. Kernmantle rope sheaths made of aramid fibers such as Technora, and Kevlar have great arc-flash qualities. Keep in mind, it is still the rope manufacturer’s responsibility to have these rope products meet the required arc-flash testing criteria.
The standard for de-electric testing is ASTM F1701. Di-electric rating typically refers to electrical tools that are non-conductive. Di-electric test are only performed on new and/or extremely clean tools – this includes rope. Although non-contaminated (clean) nylon and polyester fibers are not conductive, to our knowledge, there are no kernmantle ropes (preferred by most rescue teams) that are certified to be di-electric. This is due to the potential of micro amounts of dirt, grime, and moisture working its way into the core of the rope which becomes hard to inspect for electrical current. Most di-electric rope used by the power industries is some form of braid on braid or hollow core construction that does not meet NFPA 1983-2000 for life safety rescue rope. It should be noted that these braided ropes are still exceedingly strong but they can have compatibility issues with much of the rescue hardware on today’s market. Selected and highly training high voltage maintenance crews throughout North America are practicing rope access on live-line high voltage systems and using static kernmantle rope. However, it should be pointed out that their extreme diligence to inspection and cleanliness of their rope is second to none!
Q: What does the term “handle” mean when considering rope?
A: The handle is a reference to how easy (or hard) it is to bend the rope. Another term, “knotability”, is synonymous to the “handle”. A preferable handle would be a supple rope that is easy to tie. A tough handle might feel like you’re wrestling a section of steel cable.
Q: What does “fall factor” mean, and why is this a rope consideration?
A: The severity of a fall can by determined by an equation called the Fall Factor. The higher the Fall Factor equation, the greater the severity of the fall. The Fall Factor is determined by dividing the distance of a fall by the length of fall arrest material (i.e. rope, webbing, lanyards) in service between the load and the fall arrest anchor. Remember, Fall Factor is simply an equation, and this equation does not take into account the stretch of the arresting material. Static and low stretch rope will require some added form of energy absorbing versus dynamic sports climbing rope is designed for elongation and energy absorption.
This, in its purest form is the Ideal Fall Factor (IFF). As with all aspects of rope rigging, friction plays a major role in the efficiency of a rope system. Any and all carabiners that the belay rope bends through will create more friction, and subtract from the efficiency of the belay. So too, the coefficient of friction for the belay rope going over any surface will come into play and will in essence, shorten the belay rope and render a higher Fall Factor. This should make sense than, added friction, in effect, subtracts from the length of the belay rope in service thus giving a higher Fall Factor. This is often referred to as the Practical Fall Factor. (PFF).
One may come to the conclusion, the higher the climber is from the belayer, and the longer the amount of belay rope is in service, the lower the risk of serious injury or death from a shock loading of the belay rope. This comparison is absolutely correct. Conversely, there are other potential hazards the climber may meet during a falling event, namely, what will the climber hit on the way down before deceleration is completed? We tend to go very conservative on this, try to keep the ideal fall factor less than 0.5 with dynamic rope and zero with static rope. With static or low stretch rope serious injury may occur from an IFF of as minimal as 0.2. IFF of anything equal to or greater than a 0.33 on low stretch rope is a risk of life.