Dynamic Rope On Belay
Anybody out there on the USAR/Fire Department side of things use dynamic rope on the belay line? I've always used static on the belay and it wasn't until recently did i have the thought of using dynamic rope. What sparked this thought was a major player in the bail-out system world want to dynamic belays in their program training.
I'm sure a lot of guys have been doing this which will make me feel real stupid however I'd like some input regardless.
Our Dept. Only uses Static rope. I have always wondered why dynamic is not used for belays, as it would add some shock absorbtion during a shock load/fall. I am glad you posted this as I put my student cap on and await the responses. :<}
For a bail out kit, where you know you are going to shock load it, a more dynamic, or low-stretch (6%-10%) rope might be great. What elongation are the ropes they are purposing you look at?
Problem I see with a dynamic rope in a belay is that your fall factor will increase if loaded. If you are doing a 100 foot haul, with a rope with 6% elongation, then the first 6 feet of haul the belay is useless... if at 5 feet into the haul something in the mainline gives your load will fall to the ground.
Same with a lower or further into a haul operation. If the same 6% elongation rope is used, you have a failure with 100' played out, and you loose the main and load the belay line, your patient will travel 6 feet, which could be onto a ledge, rock, the ground or other obstical.
So no, I suppose what I am saying is that I don't want to use dyanmic rope for a belay.
We only used static. Not sure how well dynamic would work with mechanical devices which are diameter specific, such as the 540.
Great post Drew...Sometimes the obvious is overlooked. The dynamic rope has only been proposed in a bail-out training situation. Like most at work and on other teams use static with a screamer.
Definitely utilize a dynamic or semi-static rope in bailout training. They, unlike regular static ropes are designed to see a certain number of falls. We utilize dynamic rope when lead climbing, so there is definitely an application for it in the fire service. Typically you will not find a dynamic rope that is 12.5mm (1/2" rope), which is what many fire service organizations utilize for a variety of reasons, some of which may just be "that is what we have always used".
I have never been a fan of utilizing screamers in systems, as most of them are not designed, rated or tested for what we do. The NY state fire academy curriculum has not utilized them and instead has chosen to build systems with rated components that have certain dynamic qualities, such as a radium release hitch with a TPB.
Mechanical devices like the ID, MPD, 540 are designed with static ropes in mind and also should slip when their is excessive force which should give them some dynamic qualities as well, by reducing the impact to the load. If you are utilizing some of these devices in a "mirrored system", then really you would want both ropes to be static so either line could be the main in the event of a failure. I also believe that with these devices and even traditional methods, we are training to put less slack into systems than may have done previously.
Any way you look at it, we are in a very interesting time in rope work, as rope access has become a great industry, and is driving the manufacturers to develop products such as the ID and MPD and construct rope in different ways and with newer materials like 10.5 - 11mm technora ropes and semi-static ropes etc. That being said, the fire service needs to understand what rope and products they are buying and how they work together and where they should be applied. Same holds true for utilizing dynamic belays, there is a time and place for it.
I believe the Cordage Institute defines three types of rope:
static - less than 6% stretch @ 10% of the minimum breaking strength (mbs)
low stretch - 6-10% stretch @ 10% of the mbs
high stretch (dynamic) - > 10% stretch @ 10% of the mbs
because they felt there was a need to distinguish between the 0-6% range and the 6-10% range. I do not know the history of this.
My understanding is that the nylon low stretch kernmantle rope (NLSK) which rescue systems have been traditionally tested with fall into the "low stretch" category and give the best trade off between shock absorption capability and minimization of unnecessary (and possibly dangerous) bounce in the rescue system.
My knowledge of rope made with materials more modern than nylon is limited, so I can't address the performance of those types of rope. Anyone?
I always pose the follwing question to the newbies on my mountain rescue team: If we ended up with one low-stretch rope and one dynamic (climbing) rope at a rescue, which would you use for the mainline and which for the belay? The stretch in the dynamic rope is tolerable (even safe) for one but not tolerable (and dangerous) for the other.
Based on everything I've been taught, I feel dynamic rope is dangerous in rescue when used as an unloaded belay line (increased risk of hitting obstacles as the load bounces); but, it is ok (but not best) when used in rescue applications where the line remains tensioned so that the stretch has been taken out of it, e.g. as a mainline or as both lines in a two-tensioned rope lower (TTRL). The parallel plaquette rescue system developed in Colorado is one such TTRL method that uses mostly common climbing gear including two dynamic climbing ropes.
From my previous post: "Based on everything I've been taught, I feel dynamic rope is dangerous in rescue when used as an unloaded belay line..."
I'm, of course, not referring to lead climbing applications...