Dynamic ropes for belay
We are getting ready to replace a number of our older static ropes and I am considering using either a dynamic or low stretch rope (such as PMI's Impact P6) for our belay line only. Our mainline will still be 12.5mm static line. Does anyone have experience with two rope systems that use different types of rope? Another option would be to include a shock absorber on a static belay line. Any thoughts on the pros and cons of either method would be appreciated.
We use the same size rope for personnell. It is color coded to keep confusion down. Equipment/material ropes are lighter. Belay lines are same size as for job specified (people... always "personnell rated", equipment... any rating). Also, we use carabiners for just about everything.
Generally, dynamic rope is NOT preferred for a belay or hauling line in a rescue application. Dynamic ropes are designed to stretch in order to absorb high dynamic fall forces (high fall factors: fall factor=fall distance/length of rope out) typically encountered only in lead-climbing/mountaineering situations. A fall in a rescue (top-belay) situation is likely to produce only very low fall factors.
Static rope has some stretch (3-6% typically) which, combined with any "natural" slip in your system (pulleys/prusicks?) will give you good performance. Static rope will provide excellent belay performance when it is well tended (not letting a bunch of slack develop in the belay line). A "shock absorber" will not be necessary (I'm curious - what would you use?).
If you do decide to use dynamic rope be sure to understand exactly how it will perform with the belay device(s) that you use. Some do not perform well with dynamic rope/high loads, etc. You must also be aware that a failure onto a dynamic belay will likely leave your load (litter/attendant(s))much further down the cliff, etc. and produce more "bounce."
Whatever your choice - be sure your personnel know the limitations of all of the system elements and are fully trained in their use.
[This message has been edited by RWK (edited April 20, 2000).]
i have to agree Dynamic rope sould never be used as life safety rope
static line is recomended for rescue and rescue work
Corey J. Molinelli NREMT
Asst. Fire Chief
Thanks for the input.
As far as what I would use for a shock absorber there are several commercially available such as the Elk River "Zorber" or DBI's "EZ Stop Lanyard". They are common around here in industrial fall protection applications.
I would be extremely cautious about using a shock absorbing device in most rope rescue situations.
Most of those devices are designed to provide
dynamic properties to loads that would fall onto non-dynamic structures (fixed ladder rungs, rails, etc.) to dissipate the energy that would otherwise be imparted to the falling object.
Such a device in a dynamic belay scenario would likely give unpredictable performance in terms of stretch, "bounce", and other issues. Too much stretch could drop your load (litter/attendant(s) for instance) onto hard ledges, etc.
You should get plenty of dynamic performance from your rope(s) and system.
Current "static" or Low-stretch ropes provide by standard up to 10% stretch. This should be plenty for a belay line. I must disagree with earlier suggestions that dynamic or high-stretch ropes not be used in rescue. I feel they have a place in lead climbing situations where fall factors may exceed the NFPA recommended .25. These situations may be climbing up a smokestack, up a water tower, or up any other ladder to an elevated area.
BTW static, low stretch and high stretch are definitions regarding the stretch characteristics of rope, they are based on Cordage Institute standards and are different for each type of rope.
Dynamic or static rope are absolutely functional for belays or other applications.
The key is to understand/recognize the advantages, disadvantages, performance, application, etc.
TRAIN using various configurations. Make sure everyone knows how to apply the "right" tool for the job.