Belay Test Yields Surprising Results

Informal belay test reveals rescuers' slow reaction time

By Tom Pendley
Published Wednesday, June 30, 2010 | From the July 2010 Issue of FireRescue

Over the past 20 years, the concept and practice of belaying in technical rescue have been controversial, to say the least. Two decades ago, it was rare to even see a belay line in the fire service. I’d like to say we’ve come a long way since then, but have we?

In this article, I’ll briefly review a training accident involving a belay and discuss the Phoenix-area technical rescue program’s in-depth belay training with real rescue loads. I’ll share what we’ve learned from that training and outline how to perform your own belay testing. If you’re like us, the belay testing was long overdue and very eye-opening.

The Incident
Last October, a local technical rescue company was performing some crew-level high-angle training when one of the participants became injured while rappelling. At the time, his second rope belay was managed at a second anchor with triple-wrap tandem Prusiks; this is the “true” belay that we’ve always been taught is the gold standard.

During the last 30 feet of the rappel, he lost control of the brake and entered what I call a partially controlled descent. Unable to grab the brake, he instinctively reached up and clutched the fixed rappel line with his left hand. He “sizzled” the rest of the way to the ground, sustaining a rope burn to the tendon on his left hand, as well as some sprains and strains.

Yes, this was a close call, so you’re probably asking, “What happened to the gold-standard tandem-Prusik belay?”

We analyzed this incident pretty closely and concluded that it was 100 percent human error, but it seemed like those errors were awfully easy to make, and it pointed out what many of you already know: The tandem Prusik belay is not always so firefighter-friendly. There are a number of ways to mess it up.

Partially in response to this incident, we decided to conduct an informal belay study as part of our regular technical rescue training and continuing education.

The Study Objective
We wanted every technician in our system (more than 300) to belay a falling 450-lb. load. When I first suggested this at a regional meeting, safety concerns were raised, but I pointed out that 450 lbs. is actually a light load for us; we routinely belay loads exceeding 500 lbs. (Remember: A two-person load is considered to be 600 lbs.)

During this process, I hoped to document the belay drops and gather some data to help us evaluate our belay procedure and equipment. We were also interested in evaluating the role of the load-releasing hitch and what problems, if any, the Prusik-minding pulley might cause.

The Human Element
There are two basic styles of testing: One is informal backyard testing, while the other involves a formalized scientific process with rigid control. Because the latter is very difficult to conduct, the informal method is what I thought would be realistic to pull off.

One big factor in any informal study involving people: the human element. For our study, I wanted rescuers to be operating the belay when the failure occurred. And I wanted to cut the main line both while raising the test mass and while lowering it.

Most of the published drop-test studies done on belay devices have involved a tightly controlled scientific process. These studies tried to minimize variables and the human element while focusing on testing the device or technique. Personally, I’ve always enjoyed reading reports like “Are You Really On Belay?” by John Dill, but now I realize that the controlled scientific process, while valuable, leaves out some important human-factor elements.

Because a main priority of our testing was to involve rescuers firsthand, it became clear that this would be a very loosely controlled human-factor experiment in which each rescuer would perform the test slightly differently each time. That being the case, I only recorded whether we were raising or lowering, whether there was a load-releasing hitch, the generated peak force and whether the load hit the ground.

Surprising Results
We purposely did not introduce slack into the belay line during the test. We simply had rescuers prepare to belay and then confirm that the belay was ready. The rescuers made every effort to keep slack to a minimum and operate the belay using their best technique.

We focused on the tandem Prusik belay (since that’s what we use), and we created most of our failures while belaying the load going down. In some of the drops, the belay was positive with very little movement. The load barely fell, with the arresting force around 800 lbs. But in a surprising number of drops, quite a bit of rope fed through the Prusiks that were being minded, generating an arresting force of 1,600–2,000 lbs.

Remarkably, the basket often moved down 2–8 feet and frequently hit the ground. In fact, the basket hit the ground about 10 percent of the time. The rescuers involved had, on average, 8 years of experience as technical rescue technicians. They greatly anticipated the event and tried to do their best.

So, why was so much rope moving through the Prusiks? Why didn’t they lock off immediately every time? My non-scientific conclusion: If the event occurred when the belayer was in the act of minding the Prusiks with one hand free to pull out some of the belay line, their reaction time wasn’t fast enough to stop the minding action of the Prusik before a bunch of rope was pulled out. In the split-second before the rescuer stopped minding, a significant amount of rope moved through the Prusiks.

The Big Ah-Ha
The big ah-ha of this study was the realization that a rescue load (450–600 lbs.) will likely fall many feet when a main line fails while you’re using an unweighted belay line technique. This occurrence will be compounded by the distance traveled and the length of rope that is out, since more rope means more rope stretch and therefore more downward movement of the load.

Your Own Test
Setting up a belay testing drill is actually pretty easy; however, you need a site with some specific features, such as a training tower with sturdy reinforced concrete since there are a lot of forces involved. A clean cliff will also work, but you need to be able to keep the belayer from seeing the quick release.

What You Need

  • A test mass: I used eight 50-lb. bags of sand and a sturdy steel litter with bridle. I wrapped the sand bags with film, and they never broke or leaked.
  • A snap-shackle quick-release: You can purchase a good one from sailing supply stores. I recommend the Wichard snap-shackle, which you can get for $60 on the Web. The Wichard’s release string is kind of flimsy so you may need to rig something different, but the device itself holds up really well to repetitive use.
  • Sacrificial gear: Put everything you use for testing in a special pile and mark it as such. After use, keep it separate or destroy it so you don’t accidentally use it during a real incident.
  • A load cell to capture force data (optional): During our tests, I only used the arrest force data to show the rescuers that dimension. Of course, there’s a direct correlation between free-fall and high peak force. Even a little slack in the system means bigger shock force, and the instances where the Prusiks didn’t grab immediately showed up on the meter in really big numbers.

The Set-Up
To set up the drill, connect your main line and belay line to the load. Then attach the main line to the anchor with some slack in it. Use a separate rope to build a 5:1 mechanical advantage (MA) to raise and lower the load. Attach a Prusik to the main line, which will be where you connect the MA. Attach the snap-shackle release on the load end of the MA and connect it to the Prusik on the main line. Use a piece of small-diameter cord for the quick release.

Note: The edge for the main line needs a roller or some type of friction reduction, which will be specific to your site. Not having a roller makes life pretty tough for the haul team.

The belay station we used was located one floor below the haul so the belayers couldn’t see or hear the release, which is probably the best set-up for this type of drill.

One factor to consider is the edge change-of-direction for the belay. I used a piece of poly sheeting at the edge to minimize that friction factor. A more abrasive pad, like canvas, will absorb a lot of the energy, which is good for real-life incidents, but I wanted the true fall force on the belay.

Performing the Test
To run the test, position a controller at the haul station and another (preferably) to supervise the belay. Decide whether you will trip on the raise or lower. For added suspense, start at the bottom and raise up to the belay station. Then have the haul team mind the ratchet and lower the load with the haul system. Drop the load at different points each time so the belayer doesn’t know when it’s coming.

Tip: Test your current system as well as others to see how the Münter performs with big loads compared to small loads.

Remember: Instruct the haul team to lower at a reasonable, consistent pace. If they lower too fast, the belayer won’t be able to keep up. Also, communicate your ready calls with the belayer as you normally do. Tape off the drop zone below with hazard tape to prevent anyone from straying under the load during any part of the test. Remind your team that this is how you should be belaying and operating anyway.

And as always, keep in mind that safety is the most important factor. Remind everyone to watch where they stand and anticipate what will happen if something breaks or fails. Perform a clear safety check before each test, and assign a designated safety person for the drill.

Conclusion
After performing our belay study, I think I can safely say that the tandem Prusik belay is definitely one of the best means of belaying a rescue load; however, good technique is essential or it may not work as advertised, and even with the best technique, rope stretch may allow your load to move a lot. It’s well worth the time and trouble to set up belay training with heavy loads. It’s an eye-opening experience. Our personnel will be doing more testing to zero in on the technique that works best for us.

If you haven’t tested your system, your rescuers really have no idea about what will happen and how dramatic it can be. In the end, the best advice is to train consistently and frequently to develop solid fundamental individual and team skills to prevent the emergency from ever happening.

Two Types of Belays
The most prevalent definition of a belay: “A second rope attached to the rescue load, which is connected to a separate anchor and is managed by a separate person or belayer. The belayer maintains a minimum amount of slack while taking in or letting out rope as the rescue load moves up or down.”

In this most common type of belay, or back-up line, there’s some device or system in place that actuates and arrests the belay line in the event of a main line failure. For example, triple-wrap, 8-mm tandem Prusiks are commonly used to arrest a fall, but devices, such as the Traverse 540, the CMC multi-purpose device (MPD) and the Petzel ID, are all commonly used.

With the exception of the MPD, this type of belay isn’t normally under tension as the load moves up or down. The problem with a belay that’s held in reserve (without tension on it) is that we very rarely have main line failure, and the belayer very rarely has a belay actuate. It’s easy to get complacent when your success rate (in regard to main line integrity) is close to 100 percent.

Other problems with a non-tensioned belay line: slack and rope stretch. As more distance is covered with the span of rope, more potential slack and rope stretch will allow the load to move if the main line fails. For example, it wouldn’t be unlikely to see a 450-lb. load fall 10–15 feet due to rope stretch when the load is 250 feet away from the anchor. (Actually, I think that’s a conservative estimate since we saw 8 feet of movement with the load hanging on 20 feet of rope due to slack, belay technique and skill level.)

The other type of belay is simply a dual-tension system with two friction, or descent-control, devices while both ropes are under tension. In a dual system, if something happens to one rope or anchor, the other arrests and there’s very little movement since the remaining rope is under tension. A variation on the dual-tension system is to add a friction device (like a brake rack) above the tandem Prusiks on a traditional system. This removes all rope stretch from the belay, but it takes two people to operate.

Comment Now: Post Your Thoughts & Comments on This Story

After one of our rescuers sustained an injury during training, we decided to conduct a rescue belay study. Setting up a 400-600-lb. mass for the study was tricky. We used an old basket and eight 50-lb. sand bags super-wrapped with stretchy film. In this photo, the main line and release are at the top and the belay station is in the room with the open window. More distance than this is preferable, but it's what we had to work with. Note the tag line to help clear the wall. Photo Tom Pendley
Our belay anchor was at chest height (which is not typical) but it worked OK. The belayer did not know when the release would come so it was greatly anticipated. Photo Tom Pendley
On most tests, we saw about a 2' drop of the test mass. However, the basket often dropped 6-8 feet, resulting in a bounce. Members who watched the tests were amazed at this degree of movement. Photo Tom Pendley
Belay test configuration. Illustration Tom Pendley
This is one of several types of snap-shackle. If you're going to do hundreds of drops with heavy loads, buy several or at least invest in a good one. These products are designed to release sails so they can become maxed out with this kind of weight. Photo Tom Pendley


Belay Test Yields Surprising Results

Published Monday, April 18, 2011
Using experienced rescuers from the Phoenix-area technical rescue program, Tom Pendley conducts an informal test on the use of belays while both raising and lowering a load. To his surprise, results proved that rescuers’ reaction time was slower than expected, allowing a significant amount of rope to fall through the Prusik. Pendley also details how to conduct your own belay test.

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