Gear Failures. Should we worry??

Transcription

1 Gear Failures Should we worry?? A talk prepared for the New Zealand Mountain Guides Association s, December 2003, Summer Guides Course. The gear breaking machine By Mark Sedon, member of the NZGMA.

2 Introduction: Aim of Talk: -Not to make us all panic about gear failures, but to hopefully learn a bit about some situations which might lead to a accident. -If we re witness to some sort of gear failure, to be able to gather clues and make educated assessments to help an investigation. -Hand out case studies from Accidents in North America Books and ask them to write down a couple of notes on each, can be updated during talk. -Topics to be covered: -Fall Forces. -Carabiner Breakages. -Anchor Failures. -Rope Failures. -Ice Screw Failures. -Bolt Failures. -Legal Implications. -Summaries and Suggestions for safer climbing. Got my information from: How to ice climb by Craig Luebben, Internet (ie Fish web page, Chris Harmston Materials Engineer with Black Diamond, Beal web page, Patzl web page), Pit Schubert-President UIAA Safety Commission, my own research and gear destruction, five years of Accidents in North America. This is an open two way discussion. 2

3 Fall Forces: -Fall Factor (FF): = distance of fall divided by rope out. -Impact Force (IF) is the amount of weight which is felt on the body or piece of equipment, and is measured in Newtons (N). -Impact Pulse is the force that a rope undergoes while stopping a fall. -A Newton equals the mass multiplied by the force of gravity (N = kg x m/second!). -Gear is often marked in either: deca Newton (dan) which = 10 Newtons. kilo Newton (kn) which = 1000 Newtons dan = 8000 N = 8 kn = about 800kg (although not technically accurate) -The UIAA fall test drops a 80kg weight 5m on a rope 2.8m long. In effect a FF 2, but calculated at FF It drops over a 5mm diameter metal edge simulating a carabiner, and must withstand a minimum of 5 falls. A VERY HARSH TEST. -The threshold of survivability for the human body is 15 G s. This is worked out by multiplying 15 G s by their body weight. So an 80kg person can only survive 1200kg s of weight. More accurately about 12kN of force. -The UIAA (Union Internationale des Associations d Alpinism) uses 12kN as a maximum humanely tolerable load for evaluating climbing ropes. But most ropes absorb much more of the Impact Force. -If the climber s IF = 1, then the belayer must hold an IF of 0.6 (or 60% of the IF). Therefore if we add these two together the top piece of protection must hold an IF of 1.6. So 1.6 x 1200kg = 1920kg, add on a big natural rack and the load on the top piece of gear could get to almost 2200kgs or 22kN of force. What are your carabiners rated to?? -A fall onto a static sling (ie. a cows tail) from 1m above the anchor (a 2m fall) produces a dangerous 18kN of force (FF 2). 3

4 -The same fall onto a dynamic rope produces a 9kN force. If 5m above the anchor and falling 10m it produces the same FF 2 and 9kN of force. Carabiner Breakages: I tested 3 old, old carabiners. Example 1 was pulled along the long axis until failure. It was rated at 2900kgs and broke at 28kN. The nose of the carabiner, which holds the gate wire, broke off and the gate wire bent slightly. Old gear was rated in kg s, not =kn. Example 1 Example 2 was pulled along the short axis until failure. It was rated at 600kgs and broke at 5kN. It was a screw gate. Example 3 was pulled along the long axis with the gate tapped open until failure. It was not rated but broke at 8.6kN. It was rated to 3000kgs with the gate closed. Example 4 was a D shackle commonly used to connect the two chains on a Wanaka rock climbing anchor. They are not rated, but this one broke at 38kN. Discuss two case studies: 4

5 Case Study # 1: Case Study # 5. Probable cause of carabiner breaking was that the gate was open from the spine hitting the rock. Hit carabiner into palm to demonstrate. FF= 0.8, IF on top piece was 9.5kN, IF on anchor was 3.8kN, If on climber was 5.7kN. Prevention: 2 x opposing carabiners, longer draws, dynamic belay (not possible while soloing, can use pig for some dynamic value). Prevention: Belayer paying attention, moving log, taking the whiper?? Anchor Failures: I tested 3 old, old bits of webbing and 4 damaged Kiwi snow stakes. Three of the snow stakes broke between 6.3kN and 11kN by bending at the damaged area. The fourth one s sling broke at 10kN due to a sharp edge on the eyelet through which it was tied. All stakes were tested in the hard snow anchor position. 5

6 The webbing tested was all old and damaged. 6

7 Gary s old yellow webbing with what appears as oil stains on it broke at 27.4kN. Interestingly it didn t break at the knot, or contact points. The blue webbing that was half cut through by rubbing a spectra prussic against it. It failed at 3.5kN. The third webbing exploded and un-ravelled at 24.5kN. Interestingly none of the tape knots slipped. An old Troll harness which was tested failed at the tie in loop at 10.8kN. 7

8 Case Study # 2: Prevention: Check knots, back up single sling anchors, use sewn sling, stand on the sling to check, leave long tails. These have a reputation for loosening themselves. A 5-7.5cm tail is considered minimum. Case Study # 6: Prevention: Check knots, back up single sling anchors, use sewn sling, stand on the sling to check, leave long tails. Rope Failures: Give out cards and place acid and water on the table. Ask each to place their cards where they think they fit into the rope corrosion table. -The fear of rope failure comes from the time when hemp ropes were used, until the end of the fifties. If hemp ropes were wet and later dried, they dried only at the surface. Because of the capillary effect, the dampness stayed for a long time in the rope, and because hemp is a natural product, the hemp rotted. At that time it was possible to tear a used 15 mm rope by hand force. Our ropes nowadays, are much stronger than we believe (more correctly: our ropes have higher energy absorbing capacity). Within the last 19 years there were only two rope failures amongst German and Austrian mountaineers and climbers, which can t be associated with misuse or damaged ropes. The damaged ropes were due to contaminants such as acid. One reason why rope failures have reduced in Austria and Germany is because since 1983 climbers used twin ropes more and more. Twin ropes have an energy absorbing capacity over sharp edges which is, depending on the sharpness of the edge, up to double that of a normal single rope. 8

9 All rope failures happened with single ropes and in the alps while alpine climbing. But, there were another eight rope failures since 1983 not included. The causes were either a misuse of the rope or the rope was already damaged by some kind of polyamide contaminant, such as acid. Five fatalities were due to using a half rope or a twin rope in a single strand and the others were due to rope contamination. A characteristic indicative of acid contamination is the general appearance: Figure 1 shows a rope broken by the influence of acid (both ends look similar), and Figure 2 shows a broken rope, loaded over a sharp rock edge (both ends look quite different). Figure 1. 9

10 Figure 2. Figure 3 shows the effect of a sharp rock edge, small heads on the ends of the filaments, because the rope absorbs a part of the energy. Figure 3. And Figure 4 shows the filaments of a rope failure, due to being cut by a knife. Pit Schubert warns that any man who wants to get rid of his wife should be careful. Cutting can be recognized under the microscope. Last year, when he told this to some German mountain guides, one of them asked: Okay - but what shall we do then? 10

11 Figure 4. All rope failures since 1979 were because of a sharp rock edge, nothing else. He also damaged one third of the cross section of a single climbing rope, as if it had been cut by rock fall, and sent it to a UIAA-approved test laboratory. The result: The rope withstood 8 falls. Then he loaded one test sample of a such damaged rope on a static load test machine as shown. The breaking strength was 15 kn. When abseiling there is only a load of about 2 kn. Rope Failures amongst German and Austrian Climbers Year Number of rope failures Mountain or mountain range Result Wetterstein (+) Piz Palü (+) Fluchthorn (+) Sellaturm (+) Gesäuse (+) Grundschartner, Eiger (+)(+) Geislerspitzen, Westl. Zinne (+)(+) Sella, Laserzwand (+)(+) Hörndlwand (+) Hörndlwand (#) Gehrenspitze (+)(+) Years not shown: No rope failures (+) = killed, (#) = survived all climbers died except

12 -Much of the energy in a fall is converted to heat, because of rope drag through the carabiners. A lot of additional energy is absorbed, or converted to heat, by the belayer and their slippage. -The Dynamic Belay was developed during the 1930 s and 40 s in America. They used gloves to belay and let the rope run while arresting a fall. If a climber falls when he/she is 3m above their protection and 10m from the belayer the FF=0.5. If the belayer lets 2m of rope slip (which happens automatically with ATC s) the force of the top piece of protection is halved. Something to consider when selecting a belay tool: ATC or Grigri?? *******Hand this one out at end if short on time********* Petzl web page falling wizard: All examples are with 80kg climber. Example 1: Climber is 35m above the belay, 15m above pro. Belayer is using an ATC. FF=0.86. Max Impact Force (IF) on top piece of pro = 500daN. IF on climber = 300daN. IF on belayer = 200daN. Probably 8m of slippage, maybe some rope burn? Example 2: Climber is 35m above the belay, 15m above pro. Belayer is using a grigri. FF=0.86. Max Impact Force (IF) on top piece of pro = 858daN. IF on climber = 515daN. IF on belayer = 343daN. Example 3: Climber is 10m above the belay, 2m above pro. Belayer is using an ATC. FF=0.4. Max Impact Force (IF) on top piece of pro = 641daN. IF on climber = 385daN. IF on belayer = 257daN. Example 4: Climber is 10m above the belay, 2m above pro. Belayer is using an grigri. FF=0.4. Max Impact Force (IF) on top piece of pro = 500daN. IF on climber = 300daN. IF on belayer = 200daN. -To break a climbing rope a FF of 2.3 is required. Which by definition is impossible. Therefore any fall of any length is survivable, if you don t hit anything! -New ropes have some lubricant between the fibres. Old ropes loose their spring rate because they get stiffer, thus producing higher loads than new 12

13 ropes. Even though they may be of similar strength. Thicker ropes will produce higher dynamic loads than thinner ones. -The sheath equals 20% of a ropes overall strength. -Fall performance in a non-everdry saturated rope can drop by 70% when compared to a dry rope. During a fall the core fibres stretch, and the nonstretch sheath grips onto the core and prevents the core fibres from overextending. When a rope is saturated, core-sheath lubrication is greatly increased and the rope can over-stretch, beyond the point of no return. Water also dramatically weakens nylon, and if it s refrozen the situation is worsened because the ice crystals have a slicing effect during a fall. A rope immersed in sea water and dried out is also in a similar dangerous state. -Rust seriously effects rope strength, beyond what is visible. -Knots reduce rope strength: No knot = 100% Figure 8 and Double Bowline = 70-75% Double Fishermans = 65-70% Overhand Knot & Clove Hitch = 60-65% -Figure eight knot inverts at 700kgs and the rope sheath inside the knot starts breaking at 2000kgs. -Overhand knot (Euro death knot) tested with worse case scenario of 11mm rope tied to a 7mm rope failed at 818kgs. There was no slippage (but the knot was tight). -Dan Osmans death resulted in nylon against nylon. Demonstrate cutting rope with prussic. -Edelweiss developed the sharpest of edge tests. A 0.75mm radius (UIAA test is 5mm radius) 90 degree edge. Only their Stratos and Roca s Tasmania survived one UIAA drop test out of all ropes. None survived two drops. To put in into perspective, no ropes survived one drop onto 0.50mm radius and several survived on a 1.00mm radius. 13

14 -Using the rope as a belay loop formed by your tie in knot. It will hold 16kN. -FF1 falls do damage the rope and one tested by Blue Water broke after 280 falls. -Diameter and weight of ropes? Beal advises that the measure of a ropes diameter is less precise than that of the weight. -Dynamic elongation is the stretch of the rope during the first UIAA test fall. Must be lass than 40%. -Static elongation is measured under a 80kg load and must be less than 10%. Rope damaging discussion: 1. Acid 2. Battery acid probably wont hold a fall 3. Rust particles 4. A rope saturated in water weakens by up to 70% when wet 5. Permanent marker 6. Purpose made rope marker 45-50% less falls held, at mark 7. Urine 30% less falls held 8. Gasoline No acid 9. Diesel 10. Camp gas 11. Sea Water weakens by up to 70% when wet 12. Coca cola 13. Vinegar 14. Blue Water marking pen they monitor the solvents used. 15. Water 14

15 *******Hand this one out at end if short on time********* New age narrow diameter single ropes: Name: dia weight Falls IF Dynamic Static (mm) (g/m) (kn) Elongation Elongation Beal Stinger % - Blue Water Dominator % - Edelrid % Edelweiss Laser % Mammut Infinity % - Maxim Whippet % PMI Elite % - Roca Minus % Sterling Nitro % - Source: American Climbing Mag, Nov Case Study # 3 Twin or Double ropes. Case Study # 4 Twin or Double ropes. Case Study # 7 A rappeller can easily generate rope tension around double body weight with only moderate amount of bouncing. Dave McNulty s accident. Dave was descending Mt Annan with a client. He was in the lead on easy ground. Dave can only assume that the client put his hand up to steady himself under an overhang, pulled off a rock, lost his balance and the falling rock hit the rope on a sharp edge of another rock. He fell and when Dave felt a tug he turned to see the client hurtling into space. He died. I talked with Gavin Wills, a close friend of Dave s, and he said he was probably using a 11mm rope, as was standard then. Gavin also said that it was a very confusing accident, and suicide was never completely ruled out. 15

16 I tested three lengths of my oldest climbing rope. One I now feared to absail on. It had hung in the sunshine and weather at High Side in Wanaka for two years. After that it had tied stuff onto a rusty old trailer, sat in heavens knows what toxins in my car boot, towed a car and stayed wet for weeks at a time Example 1: This had a double bowline, a figure eight on a bight, an overhand on a bight, an overhand and a butterfly knot in it. It broke at the overhand on a bight at 7.3kN. Example 2: This had been cut half way through by rubbing a prussic against the rope. It broke at 3.1kN. Example 3: This was un-damaged and un-knotted. It broke at 8.3kN. I also tested some old prussic. My old faithful broke at 5.4kN, originally 600kg and maybe 6/7 years old. An old spectra prussic broke at 9.8kN which was probably 2/3 years old. Neither broke at the knots, although one tail of the double fisherman knot had slipped inside its self on the spectra. Black Diamond did some rope usage tests with a professional climber, Merill Bitter. Who was a little anal about keeping records, to say the least. It was a 10mm rope and Merill weighs about 60kgs. Rope used for 71 days hard sport climbing 628 Falls (2-25 feet) 625 lead climbs 198 tope ropes 1242 Hangs or takes 636 lowers from anchors 2 double line rappels 1 Jumar pitch 2 sections of 15 feet were cut off each end due to core shots suffered from the above abuse. One end of the rope and the middle were tested at a UIAA certified lab. The end of the rope failed on the first test at 7.45kN, the middle of the rope failed on the third test at 10.45kN (The first was 7.4kN, second 9.2kN0. Showing that IF increases with repeated falls. A new ropes IF would be about 6.5kN. 16

17 Ice Screw Failures: -Craig Luebben, write of How to Ice Climb states Good ice is really strong, and bad ice is really weak -Tests were done by Craig on ice screws in water ice. FF 1.0 to 1.7 was created by dropping a 80kg weight 5 to 9m onto 12 well placed ice screws. 7 ripped out and the carabiners on 3 broke. All 3 ice hooks ripped out. By creating a dynamic belay, reducing the FF to 0.9 to 1.2 and the same fall heights all ice screws held (still none of the ice hooks though). -The Yates screamers or similar will only take about 1m worth over energy off a fall. Only good far falls of around 1-2m. -Aerated ice is very weak! -In their testing " of well placed ice screws held static weights of kgs, enough to hold most falls. And # of well placed ice screws held static weights of 1300kgs or more (a SLCD will hold about 1300kgs). -How they failed: -Cold brittle ice would shatter. -Warm ice would deform and the screw hole would elongate. -Bulgy or convex ice would dinner plate. -After 1300kg s usually the hanger, quick-draw or carabiner would break. -A screw in good ice can be stronger than the carabiner connecting the rope. -Thicker (22.5mm) diameter screws are much stronger. To tie off or not?? In 10 tests when the tied off screw was weighted the screw would bend, then the sling would slip to the hanger. Then the screw would break or pull out, or often the sling would cut on the hanger. Nylon slings were the weakest, use spectra. 17

18 The average breaking strength was 1100kgs. Less than screws extended 5-7.5cms and not tied off. Angle the screw down and clip the hanger, or angle it up and use spectra to tie it off if more than 5cms of leverage. -Screw angle: Angling it up is like placing a stick across your leg to break it. It places higher loads on the ice surface and greater bending stress on the screw below perpendicular. Exemptions: 1. Melt out conditions exist, ie sunshine. 2. Pound ins or non-aggressive threads. 3. Poorly designed hanger, ie narrow lip. Bolt Failures: Haven t heard of any. Murray Judge replaced all the bolts on Labrinth two summers ago and was un-able to leaver the old terrier bolts out with a crowbar. Many were even damaged by avalanches and rockfall. Legal Implications: Talking with Guy Cotter, Director of Adventure Consultants, about legal implications of a equipment failure he suggests to take the time out to consider your gear, and how you think your pairs/fellow guides would evaluate the equipment. Because in an investigation, it will be someone that them who will be asked to give their opinion. Nick Craddock, Director of Mount Aspiring Guides, suggests that it will most likely be you falling hard onto your gear, and that you should be comfortable that your equipment would stand up to a FF2 incident. Chris Gore, Beal Ropes Technical Consultant, suggests to retire all ropes after a maximum of four years. But less if it s used every weekend (2 years) and as little as three months for full-time multi-fall climbing. 18

19 Summaries and Suggestions for Safer Climbing: Our gear is strong. Human mistakes are far more likely to cause injury or death. But by being aware of our equipments flaws and weaknesses is vital for ensuring carelessness doesn t creep into our systems. While guiding we often climb 50m above our anchors with no runners or belay. We should always consider our options, and err on the side of caution. For personal alpine climbing or when guiding technical routes, consider using double or twin ropes!! I have a copy of this talk on CD for anyone who d like it. 19