Mirrored Rope Systems

From SARA

Jump to: navigation, search

Kirk Mauthner Workshop with Rope Rescue Instructors Invermere, BC September 24, 2011

Participants: Rope Rescue Instructors Perry Beckham, Robin Beech, Rob McLachlan, Bob Manson, Phil Whitfield; JIBC Program Manager Jeff Cornell; Alberta Observer John Chaychuck; Consultant Kirk Mauthner


[edit] Classroom Session

Kirk apologized for confusion about his role in the RR program review and NIF grant application. Apparently, he was not any better informed than the RRIs about the NIF grant application. EMBC wanted to use the mirrored systems testing as lever to win support from other interested agencies and to help fund a general update of the RR program and was rushing to meet the application deadline.

Principles of rigging or elements of safety:

  • Safety factor sufficient to cover failures and errors (10:1 SSSF has been misapplied). Design factor, working load limit, safety margin
  • Autolocking (whistle test, hold-up test)
  • Redundancy
  • Command & communication system to overcome human failures; structure minimizes human factor errors

Factors affecting failures:

  • Methods (approach)
  • Materials (equipment)
  • Environment (hazards)
  • People

Engineering principle: If one can’t guard against a problem by engineering out, guard against it or have a warning system

1. engineer it out (design, materials, etc.)

2. guard (apply redundancy, safety factors, etc.)

3. warn (employ formal command and communications procedures to monitor hazards)

Rationale for 10:1 SSSF – partly for ease of calculation, but primarily for protection against shock load

  • fall factor 3 (1 m drop on 3 m rope with 200 kg load) is worst case;
  • provincial requirement is for no more than 15 kN peak force on anchor/system (not on person) –
  • WCB load per person is 8 kN;
  • Europe has 6 kN, so peak force would be 12 kN; typical peak force on a “competent belay” is 10-12 kN,
  • tandem Prusik belay will slip 75 cm with 25 cm stretch in the load release hitch = 1 m stopping distance;
  • rope must have 80% residual strength; must remain functional (not lose sheath, etc.)

Safety factor is ratio between breaking strength and load; 10:1 is much more than adequate at static load, but is intended to accommodate dynamic events – Note that anchoring close to an edge actually reduces amount of rope available to absorb shock load in the highest risk zone - the edge transition. Mirrored systems distribute friction and stress on each rope that would otherwise be concentrated into the single load rope.

Common principle is to go 1.5 to 2 times stronger than worst case event. Peak force on a snug belay is 2-2.5 times static load (a jolt), i.e., a 4-5 kN peak load Note technical distinction between terms “static” and “low stretch”

  • static rope - 0-6% @ 10% of manufacturer’s rated breaking strength (e.g., New England KM3)
  • low stretch rope – 6-10% @ 10% of mrbs (Blue Water 2)

On belay, peak forces on all types of rope are the same, but stopping distances will vary depending on rope design and materials. Note that tighter braided sheath of rope may reduce grip factor of Prusiks


PEP slope rescue protocols Concerns about forces are not based on actualities:

  • On 45° slope, force with four person load (subject + 3 attendants) is about 2.5 kN but this is a static load. Belay peak load is 2.5 x 2.5 kN = 6.5 kN, well within the 10:1 SSSF.
  • Note that even if a four-person load went vertical, maximum force would only be 9 kN (2.5 x 3.6 kN), also within the 10:1 SSSF.

Force limiters (e.g., a slipping clutch) need to be set between static and peak load.

  • On a Kootenay Highline, limit is around 7 kN.
  • Force limiters and safety factors should determine how we choose techniques.
  • Force limit should be below yield of material and above upper range of “jolts, shimmies and shakes”

“Conventional” two-rope system – separately anchored load and belay; presently no autolock used on descent control device. (Note Petzl I’D stopping distance on belay is longer than acceptable for BC standards.)

Consequence of failure is key to determining level of backups

Zone Risk Management

Edge transition - slipping, stumbling, load rope damage - hand-tight backup - failed system (high peak force, 1m drop, 3 m rope) - competent belay

Next section - attendant poor situational awareness leading to stumbles, pendulums - hand tight belay - command & communication

Continuation - rope induced rockfall - stop distance on shock load - twin rope tension

Bottom slope - stretcher sliding if dropped - disconnect one line and use other line to extend it as a belay

Clarifications on anchors

  • Anchor strength is rarely equal - when learning anchor systems, equalize between anchors; in advanced systems, bias subtly toward the strong anchor
  • Objective on a pre-tensioned back tie is a rigid link between the two points, not transfer of all tension to a rear anchor
  • Wrap-3-pull-2 knot is located for easier untying, not greater strength, as failure point is at the carabiner (anvil effect); wrap 2 pull 2 is as strong, wherever knot is located – advantage of wrap 3 pull 2 is only to grip the anchor; wrap 1 pull 1 would be barely adequate if angle at carabiner is less than 90°
  • Anchor extension under load - 5% elongation under static load, stop distance will be longer under shock loads – all factors (Prusik slippage, stretching load release and stretch in anchor extension could add up to 2.8m stop distance; maximum allowable should be no more than 20 cm; crucial for main line with a full load sudden edge transition or for belay with edge transitions.
  • Basket hitch – strength loss on a three-way loaded carabiner is about 33%; three-way loading across the gate is 80% strength loss – hazardous in cases where load may change to shift load points across the gate; note 50-60% loss of carabiner strength if pull if is diagonal across a D carabiner.

Command and Communication

1. role call: all positions should be actually ready, if on standby, they should say when ready

2. pre-tension; this load test may catch obvious issues (mis-threaded rack, etc.) but is not really effective as actual loads and vectors are not really simulated

3. well-controlled edge exit – attendant leans back, edge pushes out on main line, main line down slow; should be complete in 20 seconds

4. increase situational awareness of attendant – via edgeperson, control should ask about speed, edge protection, tension on belay line, how far down, fall line, etc. to monitor potential hazards

5. twin tension – only after other steps are accomplished

Discussion of RR Program Delivery Ways to convey information -

  • theory by electronic means
  • practical by field training – more support for workshop style of learning
  • continued professional development
  • annual instructor workshops are highly desirable


[edit] Field Session on Mirrored Systems

Mirrored systems were set up and operated with single-person loads, first using MPDs and pulleys and then using a 6-bar rack and a Scarab in conjunction with tandem Prusiks, RR hitches and pulley systems.

Experience with the mirrored systems suggests that they are less a radical departure from the present load/belay system than they are a series of incremental modifications to techniques with which PEP RR Program practitioners are already familiar.

Lowering Using present equipment, the system is simply set up for a lower with the current tandem Prusik belay (Radium Release Hitch, 1.35 and 1.65m 8 mm Prusiks and a Prusik-minding pulley) on both lines and a brake rack on both lines behind the Prusiks. The RR Hitch may have to be tied slightly longer than usual to by-pass the rack, but the Prusiks must remain within easy reach of the operator. One team member operates each station, minding the Prusiks with one hand using a two-finger “scissor” hold and feeding the rope through the rack with the other, using grip and angle of feed as the primary means of adjusting friction.

  • Maintenance of the “scissor” management of the Prusiks as well as a brake rack requires skill and practice and reduces the flexibility of the rack, particularly through bar spacing. The operator will might have to stop lowering to change spacing and number of bars.
  • Good coordination is required on the part of the operators of the two lowering systems in order to share the load relatively easily. However, precise equality is not essential and relative tension can easily be hand-monitored by Control or Team Leader. If tension is significantly uneven, the preferred approach is to direct the operator of the tighter line to lower faster until tension is more evenly balanced.
  • The major benefit of the shared load system is that, on a long lower, failure of one line will result in a much shorter drop onto the other line than in a conventional system where the belay line is completely unloaded.
  • The ability to shift the load completely from one line to the other if necessary is highly advantageous to help resolve problems such as:
    • Knot hang-ups on a joined line.
    • Realignment of the load to avoid obstacles on the descent route (e.g., one rope can be unloaded and flipped around a protrusion, then reloaded to shift the stretcher to a better line of descent).
  • The Scarab is easier to use as the lowering device in this application, as it relies on angle of feed and hooks to vary friction.
  • The system increases safety by ensuring that both lines are autolocking, i.e., lowering devices now meet the “whistle test”.

Edge Transitions

Because both lines are autolocking and provide equally competent belays, the load and belay functions can be shifted from one to another relatively easily. Therefore, individual lines can be alternately slackened to clip into redirectional pulleys or to allow for easy placement of edge protection.

  • In these applications, the Scarab is much easier to use than the brake rack because it is faster to attach and detach and friction can be more easily adjusted.

Raising

Changeover from a lower to a raise (or a raise to a lower) is speeded by the fact that tandem Prusiks are already on both lines ahead of the lowering devices or progress capture devices. To convert to a raise, the lowering device is removed, the rope is threaded through the Prusik Minding Pulley and run forward to another pulley attached to a haul Prusik to create a 3:1 system.

  • Note: In Kirk’s opinion, opening the PMP/Prusik carabiner to thread or unthread the rope through the PMP compromises the belay for such a brief interval that the risk of shock loading at that precise time is negligible and can be ignored. If one still considered this a risk, absolute security could be retained by ensuring that both line conversions were not occurring at exactly the same time.
  • With two 3:1 MA systems operating in parallel, the basic system is equivalent to a 6:1 MA on a single load line but enjoys less pulley drag. Most two-person loads will be easily within the capacity of a 4 person haul team, but a higher MA can be used on one or both lines if necessary to accommodate fewer haulers.
  • As with lowering, any significant imbalances in loading between the two lines will be easy to spot (especially by the haulers!) and can be corrected by direction from Control.

Use of the CMC MPD

(Refer to website http://www.youtube.com/watch?v=XhanApMKQNw and other associated sources for details). The CMC MPD (Multi-Purpose Device) is designed to deliver three distinct functions: belay, variable friction lowering and progress capture on raising. A sliding plate opens to thread the rope and a diagram ensures that load and anchor ends are clearly distinguished.

  • Belaying
    • On a raise, the incoming rope passes around a ratcheted pulley and through a V-shaped camming device. As with the tandem Prusik belay, the belayer simply pulls the rope through the device. Any sudden tug on the incoming rope trips the camming device, which closes around the incoming rope to arrest it against a stationary friction post. The effect of the V-shaped cam compressing the rope against the stationary post is even and progressive enough to avoid sheath failure.
    • When lowering, the belayer pulls the rope through the device with one hand, monitoring tension as with a tandem Prusik belay. The other hand feeds the rope into the other side of the device. Sudden tension on the outgoing rope or failure smoothly to feed the incoming rope will cause the cam to engage, arresting the rope.
  • Raising
    • The device operates as a progress capture device, exactly like a PMP and ratchet Prusik in the same way as it works for a belayed raise as described above. However, the MPD uses an extremely low-drag, ball-bearing mounted pulley that is more efficient than a normal PMP and this, combined with the fact that the camming device exerts no drag on the moving rope unless tripped (as compared with the constant friction of a snug ratchet Prusik), significantly increases the efficiency of the MPD over the Prusik and PMP on a raise.
  • Lowering
    • The device has two adjustments for manually controlling friction. A “Parking Brake” adjusts the pressure applied by the camming device to the rope, so that, when fully set, it secures the rope against any slippage. A “tap handle”, when pulled outward against a spring, uses a gear to allow camming pressure to be varied depending on how hard the “tap” is turned. This handle (like the bars on a brake rack) therefore supplies the primary friction control in a lower and is operated by one hand while the other hand grips the rope and uses variable grip strength and angle of approach to the device for finer control. A hook similar to those on a Scarab can also be used to add further friction. Release of the spring-loaded “tap handle” fully engages the camming device, providing full autolocking capability.
  • Conversion from one function to another is extremely easy and obviously much faster than in conventional systems that require addition or substitution of system components.
  • Like any specialized mechanical device, the MPD requires some practice to operate, but none of its functions seem to require any higher levels of operator skill or finesse than present tandem Prusik belay, brake rack or progress capture devices.
  • The MPD is unquestionably bulky and heavy relative to the individual components of the present system, but if present components were to be used in a mirrored system, the comparison becomes more favourable. The two MPDs required would replace 2 brake racks, 4 PMPs (one on each belay, one on each haul system), 2 carabiners (of the two used in each Radium Release Hitch), 2 10m cords and 6 Prusiks (RR Hitches and ratchets).
  • The greatest drawback to the MPD appears to be its cost, minimum $650 before taxes, which would total $1,300 per set, as compared with a conventional system total of around $310 ($125 for 6-bar brake rack, $160 for 2 PMPs, $25 for carabiner and cordage), or $620 for a mirrored system using current components. Note, however, that these conventional system components are generally already in SAR team inventories. Switching to mirrored systems with these tools would therefore require new expenditures only for additional braking devices, and here, Scarabs might be phased in because of their advantages over brake racks in terms of cost ($100 each) and ease of operation in concert with tandem Prusik belays.


[edit] Conclusions

As well as evaluating mirrored systems compared with present BC rope rescue practices, the workshop provided an opportunity to discuss various related topics, including the points raised in my September 21st e-mail note. Reviewing the points raised in the note in the light of workshop discussion:

Updating the RRTM & RRTL manuals

  • How to strike a balance between rote learning and depth of understanding?
  • RRTM level should be clear about principles behind preferred practices and should be taught and tested on a preferred, provincially consistent basic set of techniques or “standard” (defined as a measurable minimum level of performance). A basic manual could therefore be relatively simple, but it could be supplemented by a compendium of useful alternative techniques, “tricks of the trade”, etc., that could be referenced and learned once the basic certification has been achieved.
  • Videos would be very useful for basic and other levels of training, as they could be referenced for a clear understanding of preferred practices.
  • Team Leader training should place greater emphasis on full understanding of principles (theory and data), knowledge of a broader range of rope related techniques and skills and development of leadership abilities.
  • How to sort out concerns with the present manual(s)?
    • Jeff Cornell has indicated that the JIBC is prepared and funded to contract Magda Dominik to steer the process of developing new RR manuals through a process of consulting subject matter experts (SMEs) including the Rope Rescue Instructors. For efficiency in such a collaborative process, the RRIs should set up a process by which participation can be funneled both ways through key representatives. Technological advances such as use of a wiki might assist this process.
    • A first step for the RRIs will be to update any and all concerns with the present RRTM and RRTL manuals. Whitfield’s compilation from 2008-2010 might be a useful starting point.
    • Unfortunately, the NIF Grant proposal is vague about where an updated manual or curriculum fits with the testing program, analysis and training workshops. Presumably, the workshops are to be supported by reference material on any curriculum changes.
  • What is the feasibility of annual workshops of representatives of all rope rescue interests (SAR, commercial, educational, etc.)?
    • RRIs all seem to agree on the value of more frequent, hands-on workshops, for benefits of both interoperability and professional development. However, costs would be prohibitive unless ways could be found to self-fund participation to a greater extent, as with some regional workshops (NITRO) and BCCR training.
  • What is the best method of disseminating the manual and ensuring that it remains current?
    • Those working on manual revisions should consider the range of current and imminently available approaches to instruction and the dissemination of information including open-source websites and wikis, online courses, YouTube videos, etc. The objective should be to provide a system that will maintain consistent technical approaches among client groups while accommodating continuous improvement.

The NIF Project Proposal

  • Is it really necessary to invest some $75,000 in a formal testing project to provide detailed data justifying what appears to be a foregone conclusion?
    • It is now apparent that the testing project is a necessary part of the NIF Grant proposal for two reasons: 1) A number of other client agencies besides EMBC are seeking objective data on mirrored systems as part of their due diligence before endorsing these systems as an improvement on the current conventional techniques, formal acceptance of which was based on 1980s testing by the “BC Council of Technical Rescue” (essentially the PEP RRIs and Arnör Larson). 2) The testing component of the grant proposal and its benefit to interoperability greatly strengthens the application’s chance of success and supports the desired RR Program update, which otherwise would not have much chance of being funded federally as a free-standing EMBC initiative.
  • If the NIF application is not successful, is there a Plan B for updating the BC rope rescue program?
    • Probably not at this point….

The use of “mirrored systems” compared with separate load and belay systems

  • Mirrored systems appear to offer some operational and safety advantages over current rope rescue systems, both theoretically and practically.
  • Would we then retain the present tools as back up for the new, specialized ones?
    • Yes. Because mirrored systems can use current equipment and only slight modifications of basic technical skills currently in use, they could be introduced with relatively little impact on team gear requirements or training, either as “another useful tool in the toolbox” or as a new “preferred technique”. The only new, specialized tool is the MPD itself, and, though extremely efficient, it is not essential.
  • If we did, would team members then be expected to add to their already heavy burden of technical knowledge and practice by learning and being able to use both systems?
    • Our workshop experience suggests that anyone competent in all the techniques of the present load/belay system would have little difficulty in applying the same techniques to the mirrored system. Functions such as lowering through tandem Prusiks may be more complex, but conversions between lowers and raises are simpler, haul systems are simpler and edge transitions will be more easily managed. It is possible that, given a choice of which system to use, team members might find themselves favouring the mirrored system as being simpler and more efficient in more situations.
  • In the end, when the present load/belay system seems to have enjoyed an unblemished record to date, are there sufficient real benefits in moving to the mirrored system or would it be enough simply to recognize it as a alternative to the present system, comparable to the recognition we currently afford the cable rescue system?
    • As noted, even discounting the safety considerations, the efficiencies and flexibility of mirrored systems seem to make them an attractive alternative to our present load/belay approach using only current standard equipment. If MPDs are introduced, the operational benefits seem to be as jaw-dropping as the price of the gadgets.
  • Though not essential equipment in mirrored systems, the CMC MPD is obviously state of the art in terms of ease and efficiency of operation. Because of its cost, it should be considered as an optional piece of equipment, and any team choosing to use it should still be expected to be proficient in the conventional load/belay system and the use of “conventional” equipment in a mirrored system in order to ensure that different teams can still work together with common systems whenever necessary. (A parallel might be the requirement that rope team members be able to use Prusiks for SRT ascending, even though they may be more proficient (and efficient) in the use of mechanical ascenders.)
  • If those of us participating, all of whom have considerable and varied experience with ropework, come away impressed with mirrored systems and endorse their adoption, what if any effect will this have on the program?
    • First of all, those of us who were lucky enough to get our hands on the system need to afford similar opportunities to the other RRIs as soon as possible, as we think the mirrored system will sell itself pretty well once tested and understood first hand. If, either through trust of our judgement or personal experience, our fellow RRIs buy into the value of mirrored systems, the techniques can presumably be tried by various teams under proficient direction. Apparently at least two teams are already using them.
    • Through the NIF Grant proposal, EMBC is already positioning itself to accept them as part of the rope rescue program, but if the testing takes a year and the training based on curriculum changes is to occur in the second year, the new curriculum and any teaching aids, including manuals, may have to be developed in the first year concurrently with the testing. Presumably therefore, EMBC must instruct the JI to start almost immediately on the new curriculum development somewhat on speculation, and our role will be to feed into the process our direct practical experience of how our teams perform in tests of the mirrored systems and any other “new” techniques that we believe would be worth including in the basic course(s) or in supporting supplements

Delivery models for the EMBC Rope Rescue Program

  • All present, including Jeff Cornell, agreed on the desirability of developing a more flexible system than at present for delivering a consistent core rope rescue curriculum. The curriculum would be shared by all interested parties, any of which, with suitably qualified instructors, could teach, evaluate and certify to the standards of the curriculum according to individual purposes. Updates would be made through a collaborative process involving all parties, both to maintain consistency and ensure cross-pollination of ideas and techniques.
  • Initiative for leading this process probably rests with EMBC, though detailed process design could be delegated by contract or other means.
Personal tools