Mountain and cave rescue teams have long used 1 tubular webbing in rescue operations. Much of what the fire service learned about rescue came from these teams and therefore we also learned about their use of webbing. This article will demonstrate how one piece of 1" tubular webbing used to create a wrap 3 pull 2 anchor secured with a water bend is a strong and secure anchor.
Traditional Webbing Use
The greatest advantage of 1" tubular webbing is its versatility. It's lightweight flexible and lacks bulkiness-all big advantages over manufactured anchor straps particularly if rescuers must climb a vertical rock face a steep trail or even a tower to locate or extract a victim. Anchor straps may be faster to rig but if it takes a team an hour to hike or climb to a victim what difference will it make if the team takes 60 additional seconds to tie a wrap 3 pull 2 with webbing?
When we first learned to use webbing for anchor material we were taught a) to always secure the ends with a water bend and b) that one piece of webbing tied in a loop would fail at approximately 5 000 lbf. Many people refer to this as a wrap 1 pull 1 and the point of failure usually occurs in the water bend.
In the fire service many of us attempt to maintain a 10:1 static system safety factor-static meaning before the occurrence of a dynamic event such as a fall or a drop. Many consider our maximum safe working load to be 600 lbs.; so 600 divided into 5 000 results in a little more than an 8:1 safety factor. To increase our system safety factor at the anchor many fire service personnel use two separate pieces of webbing that are tied the same length to create a strong anchor.
From personal observation I can attest that this does work. For a period of 4 or 5 years in the early 1990s Russ Born the godfather of modern rope rescue in Ohio performed drop tests during his annual rope class at Bowling Green (Ohio) State Fire School. After seven or eight drops with approximately 520 lbs. one of the pieces of webbing would fail and the second piece would prevent the mass from impacting the ground.
When we went to a wrap 2 pull 2 or a wrap 3 pull 2 we still used two pieces of webbing. The justification: Many of us in the fire service don't train enough or use rope on a regular basis and it was thought that two pieces of webbing would overcome problems posed by poor critical angles used or damaged webbing and improperly tied water bends. However tying two separate wrap 3 pull 2 pieces of webbing to make them the same length is time consuming and frustrating.
Another Webbing Option
In the classes we teach at Cuyahoga Valley Career Center in Brecksville Ohio and on rescue teams in the area we've been using one piece of webbing to tie our wrap 3 pull 2 anchors for a number of years now. But new members or members who have taken other classes often question this practice.
The wrap 3 pull 2 with 1" tubular webbing has an additional benefit largely unrecognized in the fire service: the tie used to secure the webbing. Mountain and cave rescue teams might be more proficient at tying a water bend than members of the fire service because many of us don't train enough and/or we don't get enough calls that require it. Further these teams may receive an equally low number of callouts but they can better tie knots bends and hitches as these skills are often related to their mountaineering and caving hobbies.
To secure the ends of webbing the objective is to tie a water bend. An incorrectly tied water bend may result in an overhand knot. If we aren't sure how to tie it we may revert to our Boy Scout training and tie a square knot but if we incorrectly tie the square knot we can end up with a granny knot.
With this in mind I would like to present some data from testing we conducted in July 2005 which will demonstrate why a single piece of webbing tied in a wrap 3 pull 2 could be considered acceptable to people who have long used two separate pieces of webbing to create an anchor as well as to people who rely solely on manufactured anchor straps.
We performed this testing to determine the failure point in 1" tubular webbing when rigged as a wrap 3 pull 2 and tied with different bends. We used new 1" tubular webbing purchased from PMI. The webbing was tied around an 8 ÃÂ« -inch-diameter log with a circumference of approximately 27 inches. The interior angle of the webbing at the point of pull was less than 30 degrees. We tested four ties-the water bend the square knot the overhand knot and the granny knot-three times each.
It appears that all the failures from these tests occurred over the carabiner and not in any of the ties. The test results:
1" Tubular Webbing Failure Points for 4 Ties When Rigged as a Wrap 3 Pull 2 (See figure 1)
We repeated this same testing but tied our wrap 3 pull 2 webbing around a smooth 4" steel bollard rather than the log. The results: (See figure 2)
Our point here was to show that one piece of webbing used to create a wrap 3 pull 2 anchor secured with a water bend is a strong and secure anchor and that when using a wrap 3 pull 2 the tie used to secure the ends of the webbing is not as important as we were taught to believe. None of these slow-pull failures occurred in the water bend overhand knot square knot or granny knot-except the one that slipped out of the granny knot at 4 535 lbf. and if you're using 11-mm rope that's a little less than what the rope will fail at with a knot in it. So the point of failure when using a wrap 3 pull 2 secured with a water bend is in the webbing and not the tie. And if the water bend is tied incorrectly it still fails in the webbing and not the tie. This appears to be a previously unrecognized benefit of using a wrap 3 pull 2 with 1" tubular webbing.
I say "previously unrecognized" because the indicators were out there but the rescue community failed to recognize them. In 2000 John McKently and Bruce Parker from CMC gave a presentation at the International Technical Rescue Symposium (ITRS) on 1" webbing anchor tests. They performed 15 tests on 1" needle loom and 1" shuttle loom tied in a single loop and secured with a water bend and five tests on 1" flat webbing. They repeated these tests with the webbing tied as a double loop and then as a wrap 3 pull 2.
They ultimately performed 20 tests of 1" webbing tied in a single loop and secured with a water bend; 20 tests with 1" webbing tied as a double loop and secured with a water bend; and 20 tests with the webbing tied wrap 3 pull 2 and secured with a water bend. The results: All 20 tests with webbing tied in a single loop failed in the water bend and all 20 tests with webbing tied in a double loop failed at the inside loop of webbing at the pin as did all 20 tests of the wrap 3 pull 2. So it appears that when multiple loops of webbing are stacked with one loop on top of another the failure point is the loop on the bottom and not the water bend.
In our testing we took this one step further replacing the water bend with different ties and the results remained the same. The failures occurred where the webbing was stacked upon itself and not in the tie that secured the ends of the webbing. A total of 64 tests of 1" webbing tied wrap 3 pull 2 were performed in the two studies and not a single failure occurred in the tie that secured the ends of the webbing. This is the previously unrecognized benefit of using a wrap 3 pull 2 with 1" webbing.
The results of these tests underscore what we can learn from the mountain and cave rescue community: that using one piece of 1" tubular webbing to create a wrap 3 pull 2 anchor secured with a water bend is a secure anchor that can be of great use to the fire service.