Static Load Analysis for Alpine Rescue System - 2017

Static Load Analysis For Alpine Rescue System - 2017

“Original” Parallel Plaquette Set Up Using Two Black Diamond ATC Guides

This system uses one Black Diamond ATC Guide as a descent control device (DCD) and is located towards the load. A second ATC Guide is used as a plaquette device and is located towards the anchor. The DCD is rigged in the belay mode and the plaquette in the auto-lock mode.

Anchor point is a wrap three pull two hitch (W3P2) using Sterling 11/16” tubular webbing.

1. MBS webbing = 3,000lbf or 13.3kN.

2. Theoretical strength with water knot isolated in the front is 12,000lbf.

3. Actual breaking strength for a 1” tubular webbing W3P2 is 47% of theoretical (this is the MBS value)1.

4. Assume breaking strength of 11/16” W3P2 is 5,640lbf or 25.1kN.

Carabiners are Petzl Spirit screw lock gate.

1. MBS major axis is 23kN, gate open is 9kN and minor axis is 8kN.

2. Gate opening is 19mm.

Rigging plate is a Petzl Paw.

1. MBS is 36kN.

2. One top hole and three bottom holes big enough for screw gate carabiners.

Slings are Mammut Contact pre-sewn.

1. MBS is 22kN.

2. Blue edge slings are 8mm x 48” and red edge slings are 8mm x 24”.

Rope control device is Black Diamond ATC Guide.

1. MBS is not known, including MBS for the large eye used in auto-lock mode.

2. Parallel plaquette use of the Black Diamond ATC Guide has been tested using British Columbia Council of Technical Rescue (BCCTR) Belay Competence Drop Test Method (BCDTM) 2. The BCDTM uses a 200kg mass dropped 1m on 3m of rope. To pass, the rope can’t extend more than 1m and the maximum force must be less than 15kN.

3. Results for the Black Diamond ATC Guide were a maximum force of 13.7kN and maximum extension of 47cm (n=10) 3, 4.

Rope is Blue Water 3/8” Safeline with a polyester sheath and a nylon core.

1. MBS is 6,766bf or 30.1kN.

2. Elongation at 300 pounds is 2.8 percent.

3. Figure 8 On A Bight knot reduces strength from 14 to 35 percent, with reported values of 20%, 23% to 34%, 20% to 25%, and 20% to 25% 5, 6. To be a bit conservative, assume a reduction of 30 percent.

4. High Strength Bowline is a knot that has not been tested at all that I can find. For a normal bowline knot, it reduces strength from 29 to 58 percent, with reported values of 33%, 26% to 45%, 25% to 30% and 25% to 30% 5, 6. To be a bit conservative, assume a reduction of 35 percent.

5. Given a 35% reduction due to knots, the MBS for the rope is 4,398lbf or 19.6kN.

6. This rope does not quite meet the 20kN safety margin, which is a point for debate on the appropriate use for this rope and the system as a whole.

Pulleys are Petzl Gemini (double) and Petzl Mini (single) or CMC Protech Double and CMC Protech Single.

1. MBS for the Petzl pulleys is 23kN.

2. MBS for the CMC pulleys is 43kN.

2. These are all prusik minding and have an efficiency of around 90 percent.

Accessory cord is 7mm Sterling.

1. MBS is 2,788lbf or 12.4kN.

2. MBS for a prusik loop is not the theoretical doubling of a single strand minus knot reduction. It seems to be about 2kN more than a single strand 6, 7. MBS for 7mm cord on 11mm static rope is 11.4kN.

3. Prusiks seem to break and not slip. 196 out of 203 samples had the prusik break. It does not seem like a good assumption that the prusik on a haul system will slip before it breaks.

4. The MBS of a single 7mm prusik on 11mm rope is WAY below the 20kN safety margin. Prusiks should be carefully evaluated and not relied on to hold a rescue load.

Edge attendant and haul system rope is Blue Water 9mm Search Line with a Technora sheath and nylon core.

1. MBS is 7,081lbf or 31.5kN.

2. Elongation at 300 pounds is 3.8 percent.

3. The Technora sheath is an unknown for impact on knot reduction in rope strength. Technora is very abrasion resistant. Technora can be degraded by UV light. One note mentioned a possible 50% reduction after 3 months of exposure. The note did not have any details. Use of a similar material (aramid) as a prusik seems to cause some problems, mainly a greater variability of results in drop and slow pull testing 8.

Modified “Original” Parallel Plaquette Set Up Using One Black Diamond ATC Guide And One Conterra Scarab

This system uses one Conterra Scarab as a descent control device (DCD) and is located towards the load. A Black Diamond ATC Guide is used as a plaquette device and is located towards the anchor. The ATC Guide is rigged in the auto-lock mode. Everything else is the same as the “original” parallel plaquette set up.

Rope control device is the titanium Conterra Scarab

1. MBS for the frame is ever 40kN.

2. MBS for 11mm rope is 20kN for nylon/nylon and 23kN for polyester/nylon. The rope breaks at the nose of the Scarab MBS is a bit more than the knotted strength of the rope.

CMRU Modified Parallel Plaquette Set Up Using One Black Diamond ATC Guide And One VT Prusik

This system uses one Black Diamond ATC Guide as a descent control device (DCD) and is located towards the anchor. A Blue Water VT Prusik tied is used as a plaquette device and is located towards the load. The ATC Guide is rigged in the belay mode.

Rope control device is the Blue Water VT Prusik with a Technora sheath and a nylon core

1. MBS end to end is 19.5kN and in a basket hitch is 28.0kN.

2. The VT Prusik in a 6 over 1 configuration shows slippage at 7 to 14kN.

3. The VT Prusik can be tied in a few ways, including a 6 over 1 and Valdotain Tresse hitch. For this set up, the VT friction hitch is used.

4. The VT friction hitch can be released under a load.

5. Use of the VT friction hitch as a belay device was tested using the BCDTM. Using a 6 over 1 hitch, over 27 drops, the VT Prusik passed the majority of the drops. Rope extension ranged from 28 to 109cm (> 100cm fail ) and arresting force ranged from 8 to 13kN (> 15kN fails) with mild to moderate sheath glazing on the host rope 8, 9.

6. During slow pull testing of the VT Prusik configured as a 6 over 1 friction hitch, there was very little visible damage to the host rope or the prusik 9.

7. At this point in time, use of the VT Prusik as a VT friction hitch on the load side of the alpine system seems reasonable.

References

1 Empirically Derived Breaking Strengths for Basket Hitches and Wrap Three Pull Two webbing Anchors. 2011. Thomas Evans and Aaron Stavens. Montana State University, Department of Earth Sciences, Bozeman, MT.

2 Rescue Systems Testing: Background and Summary. 1990. Arnor Larson. British Columbia Council of Technical Rescue, Research Section, Invemere, BC.

3 Parallel Plaquettes: A lightweight Rope Rescue System Using Common Climbing Equipment. 2009. Mike Gibbs. Rigging for Rescue, Ouray, CO.

4 Rescue Belays: Important Considerations For Long Lowers. 2007. Mike Gibbs. Rigging for Rescue, Ouray, CO.

5 A Review Of Knot Strength Testing. 2016. Thomas Evans. SAR3. sarrr.weebly.com/sar3-original-research

6 Rope Strength And Reduction In Strength Due To Knots. 2011. Jerry Heilman. Corvallis Mountain Rescue Unit, Corvallis, OR.

6 Empirical Breaking Strengths Of Single Prusiks Of Four Diameters On 11mm Static Rope. 2014. Thomas Evans. Western Washington University, Geology Department, Bellingham, WA.

7 Slow Pull Testing Of Progress Capture Devices. 2014. DJ Walker and Russell McCullar. International Technical Rescue Symposium, Denver, CO.

8 Friction Hitches For Technical Rescue: An Open-Ended Approach. 2015. Kevin Koprek. International Technical Rescue Symposium, Portland, OR.

9 High Modulus Aramid Fiber Friction Hitches In Technical Rope Rescue Systems. 2014. Mike Gibbs. International Technical Rescue Symposium, Denver, CO.