Decenders FAQ

Decenders Q & A

Q: What types of descenders are available and how do you know which one to choose?
A: Like rope grabs there are a zillion descender and friction control devices on the market. Friction control devices (descenders) are as old as mankind. They can be as simple as adding a bunch of wraps around a tree or as complex as the MPD. All of them accomplish their goal of applying friction at a slow and controlled speed. Friction control is a key physical component in rigging. We’re trying to overcome friction during the hauling process, and we’re trying to use it to our advantage during the lowering process.

Friction control of these many devices is done by bending the rope and creating a greater composite angle of contact between the stationary device and the moving rope. Example: if a rope is lowered over a simple 90 degree wall there is a 90 degree angle of contact; when you apply two round turns of the rope around a handrail there is 540 degrees of contact (hence the reason behind the name of the 540 belay device). A six bar brake rack will apply approximately 720 degrees of contact when fully loaded, the more you squeeze the bars together the greater the angle of contact and the slower the load will move until it simply stops.

This friction stuff is all fine, but what makes a good friction control device?

  • The device should be simple to learn and easy to use. We prefer the Petzl I’D for most rope access and rescue applications due its intuitive friction control handle, ease of learning and overall durability and reliability.
  • The rope should bend through the device in an in-line fashion as opposed to a curling or coiling fashion. Curling the rope under tension (especially with kernmantle static or low stretch rescue rope) tends to introduce curling and tangling memory into the rope when it becomes unloaded (kind of like curling ribbon with a scissors when wrapping a present). This is a rope maintenance problem with devices such as a rescue eight or various manufactured forms of tubes.
  • It should be manufactured by a recognized company with a history of quality products and reliable support.
  • The device should have a proven history of high performance and customer satisfaction.

Q: What is "anti-panic"?
A: An anti-panic feature is typically associated with friction control descent devices. These devices have a friction control handle that when over pulled or activated the device will auto-stop. This allows the user to simply reset the handle and continue in at a more controlled speed. Most descent devices do not have this type of feature and when the control handle is pulled wide open you will fly whether you want to or not. As stated above, we prefer the Petzl I’D for the best performing descent device that incorporates an anti-panic feature, the handle is extremely intuitive in its design.

Q: Will a descender work on any type of rope? What about the rope diameter?
A: Brake racks typically work well with either ½ inch or 7/16 inch rope. However, racks are quickly loosing favor to the Petzl I’D and the CMC PMD because these devices are so useful and easy when converting a lowering system to a hauling system. The Petzl I’D and the PMD are outstanding and highly recommended devices for rope access and modern rope rescue, but they are rope diameter dependent. For ½ inch (12.7mm) rope you must use Petzl I’D L (Red), likewise for ½ rope you must use the Red MPD. For 7/16 (11mm) rope you would use the Petzl I’D S (Gold), and for the MPD you would use the Silver 7:16 (11mm) version.

Q: What anchor position options are there for descending?
A: There are only two options for rigging a descent device. It can be at the FIXED position at the anchor or it can be at the TRAVELING position on the person descending.

The Fixed position at the anchor is always used during team-based operations when the load is being lower by another individual who is controlling the descender. With the fixed position it should be noted that the standing part (the rope bag) is up by the anchor and the working end (end of the rope coming out of the bag) is tied to the load.

Whereas with the Traveling position, the descent device is attached to the individual who is descending (rappelling) and in control of the device. The rope bag (standing end) is over the edge and the end of the rope is tied to the anchor on top.

G October 11, 2016
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