Hot Knife Through Butter.
How easy (or hard) is it to cut caving stuff?
by Scott McCrea
I wanted to know how easily the things we hang from while vertical caving could be cut. I have heard about people trying this but I've never seen it. Now, through the use of modern technology, you can see it too. The clips discussed here, as well as the full-length video, are available below.
This experiment is not overly scientific. In fact, we had numerous factors that we could not control. We tried to cut each sample slowly and then quickly. We used 200 pounds of weight with each sample, with a few other variables on some. We tried to do things in an orderly manner so hopefully this will be useful information.
We tried to use a set up (Figure 1) that would minimize the waste. We attached a Petzl Croll to the clothesline post. Then we put the very end of the sample in the Croll, with only an inch or so above the cam. Using a Petzl Tibloc, we attached the load to the sample and hoisted the load a couple inches off the ground. This method made it possible to waste as little as 3 inches per sample. We can't afford to be hacking up our ropes.
We cut the samples with a Petzl Spatha Knife (Small) (Figure 2). It has a partially serrated edge. It was pretty sharp, but not new. We also used a pair of Cutco scissors, a Mike's Lite carbide cap lamp and a sharp hunk of northeast Tennessee limestone.
The complete movie:
"Hot Knife Through Butter."
Short clips from the complete movie:
Sample 1: 11mm (7/16") PMI Max Wear rope, very common caving rope. It is about 10 years old and has seen lots of use. First we tapped the rope with the knife. Nothing happened. Then we sawed back and forth with light pressure. We found the sheath to be pretty tough but once we got to the core, the cutting was much easier. The fast cuts were impressive but they were not easy. A strong grip and good pressure on the rope was required. The swipe cut took three swings, but with some practice, I probably could have done it in two.
11mm (7/16") PMI Max rope, 200 pound load.
Cut with Petzl Spatha Knife (Small). Slow cut.
11mm (7/16") PMI Max rope, 200 pound load.
Cut with Petzl Spatha Knife (Small). Fast cut.
Next, we added more weight to the PMI rope. We wanted to simulate a rescue or tandem load. Jimmie stood in a loop attached to the Tibloc. This added about 200 pounds to the load. As expected, it was easier to saw through the rope with the added weight.
11mm (7/16") PMI Max rope, 400 pound (rescue) load
Cut with Petzl Spatha Knife (Small). Slow cut.
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Sample 2: 8mm accessory cord, manufacturer unknown. We find this cord to be common among cavers for cow's tails, QAS lanyards, foot loop lanyard and various other things. So, of course, we better see how easy or hard it is to cut. We tapped it. Nothing happened. Light sawing showed us that it was pretty easy to cut. The fast cut was very easy. It did not take much effort at all.
8mm accessory cord, 200 pound load.
Cut with Petzl Spatha Knife (Small). Slow cut.
8mm accessory cord, 200 pound load.
Cut with Petzl Spatha Knife (Small). Fast cut.
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Sample 3: One inch tubular webbing, manufacturer unknown. Webbing like this is very popular with cavers, climbers and even normal people. Tapping did nothing. Light sawing went through in three strokes—not hard to cut at all. The swipe cut was also easy. Effort needed to cut one inch webbing is very similar to that of 8mm accessory cord.
1 inch tubular webbing, 200 pound load.
Cut with Petzl Spatha Knife (Small).
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Sample 4: 5mm Maxim Tech Cord. This cord is very strong. It's rated to hold 5000 pounds. Some cavers looking to shave weight and bulk from their gear have started using this cord for lanyards and foot loops. Climbers also use it for slinging chocks and other things. This was the first sample piece that we saw visible damage from tapping. The slow cut was very easy. The fast cut was also very easy. Of the things that we tested, this was the easiest to cut.
5mm Maxim Tech cord, 200 pound load.
Cut with Petzl Spatha Knife (Small).
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Sample 5: Same PMI rope as tested before and a Mike Lite carbide cap lamp. There is a myth that carbide and vertical caving don't mix. So, we had better test it. The flame on the light was about one inch long. It took over three minutes to completely burn through the rope. We could have done it much faster, but the carbide was not fresh and we had to shake the light periodically. I estimate that, in ideal conditions, we could have burned through in about one minute, even faster with a more powerful flame, like a ceiling burner.
11mm (7/16") PMI Max rope, 200 pound load.
Cut with carbide cap lamp.
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Sample 6: Same webbing as tested before and a Mike Lite carbide cap lamp. Rope is not the only thing a vertical carbide caver needs to worry about. The webbing was cut in about 13 seconds. It could be seriously damaged much faster. A more powerful flame could damage or cut webbing very quickly.
1 inch tubular webbing, 200 pound load.
Cut with carbide cap lamp.
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Sample 7: Same PMI rope as tested before and a pair of Cutco scissors. Some cavers and rescuers carry scissors in place of a knife. It is not easy to cut loaded rope with scissors. Rocking the scissors up and down helped to cut faster. Once the sheath is cut, the core cuts quickly.
11mm (7/16") PMI Max rope, 200 pound load.
Cut with heavy duty scissors.
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Sample 8: Same PMI rope as tested before and a sharp hunk of northeast Tennessee limestone. This not an efficient way to cut rope. It took 18 swipes to cut the rope. But, these swipes could be similar to the sawing action produced the stepping/standing action of a vertical caver. 18 steps can happen quickly.
11mm (7/16") PMI Max rope, 200 pound load.
Cut with sharp, limestone rock.
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Here's what we learned:
- The thicker it is, the harder it is to cut. What more can I say?
- The sheath is very important in protecting a rope. The bulk of the strength of rope is in core, but once the loaded core is exposed, it's pretty easy to cut.
- While cavers need to be concerned about protecting their ropes, they need to take even greater care with the cords and webbing they carry.
- Avoid exposing your ropes to sharp rock edges.
- Using a knife around loaded rope, cordage and webbing is dangerous.
A special thanks to cavers, Jimmie Deaton and Dan Henry for helping me with this experiment.
Thanks to SWAYGO for hosting the videos.
Figure 1
Figure 2
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Other thoughts related to the topic:
Here's a telephone pole lineman training video, where the trainee tries to rescue a training dummy. He is being timed and needs to hurry, so he whips out his knife and...
http://www.StupidVideos.com/?VideoID=737
Here's an interesting web site: http://www.oregonknifeclub.org/rope.html. This is a club of folks that cut rope for fun. Pretty impressive.
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Can't view these movies? Get Quicktime.
Copyright 2004 Scott McCrea. All rights reserved. Feel free to link to this page. Please do not repost, republish, distribute, hot-link, etc without written permission first.