QC LAB: HOW STRONG ARE HIMALAYAN FIXED LINES?

Our QC Lab posts aim to answer some of climbing's most common gear-related questions. This month features fixed ropes from the Himalayas.

I just got back from a month of volunteering at the Khumbu Climbing Center in Nepal. It was quite an experience to say the least. Crushing, however, was looking at all the amazing Himalayan peaks all day and not being able to climb any of them—I guess I'll just have to go back.
The stunner of course was Ama Dablam—just have a look—enough said. One of the Nepali instructors had guided Ama Dablam 18 times, so naturally I was grilling him for beta: not too high (6,812 meters / 22,349 ft), not too cold, climb it in the fall, kinda crowded, interesting and varied climbing, some fixed lines. Fixed lines? I immediately wondered what they used, what diameter, how heavy it was, how long it stayed in-situ, how it was fixed on the mountain, etc.
Ironically, as I arrive jet-lagged back in the office last week, one of the other engineers here here in the lab had a section of some sketchy looking rope on his desk. It turns ou that his buddy guided Ama Dablam last fall and took some of the fixed line off the mountain and sent it over so we could have a look and do some impromptu testing. Thanks to Peter Anderson for thinking of us, for the photos and congratulations on a great summit.

SAMPLE

From fixed lines on Ama Dablam
3 strand "Korean" fixed line, looks to be about 8mm (maybe 3/8")
Guessing that it's polypropylene

TESTING & RESULTS

All tests were simple slow-pull tests to failure in our trusty tensile testers. Values shown are ultimate strength in that particular configuration and where the failure occured. Just for point of reference, a sewn sling must meet 4946 lbf to be CE certified.

Single Strand: The strength of one single piece from the sample, pulled between two rope clamping fixtures.1. 2022 lbf, rope @ fixture
Figure 8 Knots: Exactly how it sounds - a Figure 8 knot on each end of a sample, non-dynamically loaded to failure. 1401 lbf, rope @ knot
Tied into a loop w/ a Fisherman's: self explanatory - and how this cord was seen used a lot on the mountain. 2016 lbf, rope @ pin
Ascender on single strand: one end of the rope with a figure 8 using a pin to attach to the tensile tester, while an ascender is clamped to the rope and also connected to the tensile tester. Slow pull to failure. This is a typical CE test configuration for ascenders. 735 lbf (less than the CE Ascender proof by 165 lbf), rope @ ascender
Clove hitch on RockLock carabiner: a RockLock is a carabiner with a large rope bearing surface and round cross section. A clove hitch is a knot commonly used for connecting fixed line to carabiners which are in-turn connected to anchors on the route up the mountain. 1270 lbf, rope @ knot (minimal slip)
Clove hitch on VaporLock carabiner: A VaporLock has a smaller rope bearing surface and more of an I-beam cross section. 1087 lbf, rope @ knot (minimal slip)
Rope loop through picket eye: Some of the fixed line was connected directly to pickets buried in the snow so we tested a sample in this configuration. 1879 lbf, rope @ picket

THOUGHTS

I don't think I've heard of fixed lines snapping too often in the Himalaya or anywhere for that matter
Obviously it's a fine balance between weight and strength—someone has to carry these spools of fixed line at high altitude in order to prepare the route for clients or others, but it's got to be strong enough to be able to withstand the rigors of many people jugging, weather, UV, etc.
My guess is plummeting down a fixed line and slamming into the next anchor could generate loads in excess of some of the values seen above - though the amount of stretch and give, if any, in the anchors will help reduce this.
It would be conceivable to shock-load an ascender to values greater than that seen above.