Rope Rescue Long Lowers
On Long Lowers: A Discussion Paper
Written by Kevin Ristau
At suspension heights of over 30 metres, it becomes increasingly difficult to operate Belay Control Devices (BCD). The weight of the rope, wind loading, and operator fatigue must be overcome in order to operate a BCD properly.
When a load is transferred from one rope to the other, the load will apply a force to the belay rope that is relative to its mass and velocity, and this force will stretch the rope. The current recommended best practice from the International Technical Rescue Symposium (ITRS) is that a 10% allowance must be made for rope stretch before the belay system arrests a fall due to a failure in the mainline. At 30 metres, this can contribute 3 metes to the Total Fall Distance (TFD). Given a Tower Crane elevation of 196 metres (Port Mann Bridge replacement), we must consider the possibility that a failure of the mainline during the last 20 metres of the lowering operation will result in a ground strike. This is exclusive of any dynamic forces caused by slack in the belay rope or anchor system stretch.
It is desirable to maintain as much control of the rescue load at all times as possible. Therefore minimizing movement of the load during a mainline failure at any time, not just when within ground strike potential, should be the goal of any belay system.
The recommended system for lowering at elevations greater than 30 metres is the two-tensioned rope lower. Twinned lowering systems share the load between two ropes and descent control devices, pre-tensioning each system to take up as much stretch as possible.
The combination of descent control devices and belay control devices on each line limits potentially unsafe Total Fall Distance by sharing the load between both ropes.
The use of a Descent Control Device (DCD) to tension the safety line prevents the weight of the rope from locking up the Belay Control Device (BCD), and allows the BCD to be properly operated. This also prevents any slack developing in the belay system and minimizes rope stretch in the event of a mainline failure.
No system can remove all of the rope stretch. The goal is to reduce Total Fall Distance (TFD) and rope stretch as much as possible to provide the greatest margin of safety.
Rope stretch on a non-tensioned line, with no slack in the system, is a factor of the Universal Spring Constant, which is a force of 2.5 times the load when using rescue rope.
A rescue load of 280kg, which imparts a force of 2.8kN when hanging statically on a rope, will impart a force of 7kN on a taut, non-tensioned belay line upon failure of the mainline.
280 kg mass, 0 cm drop, on 30 m of rope (12.5mm PMI EZ Bend), results in 1.9 metres of extension (6.3% stretch) with a 6.1kN MAF (Maximum Arrest Force, measured at the anchor).
This represents the absolute minimum amount of rope stretch possible with current two-rope rescue systems, where the belay line is not tensioned and there is no free fall. Any slack in the belay system will create free fall. Free Fall is a dynamic event that will increase the force impacting the belay line, and therefore increase TFD, rope stretch, and MAF. Rope stretch will increase proportional to the amount of slack in the belay line and the dynamic movement of the load. Allowance must also be made for any Energy Absorber Extension – if used , also known as Deceleration Distance (DD), when calculating TFD if your system uses energy absorbers.
In the case of long lowers (greater than 30m) rope stretch becomes unmanageable, and this is when the use of the two line tensioned lower becomes practicable. By transitioning to a twinned system, where the main and belay lines mirror each other, the rope stretch potential in the event of a failure of either line is minimized. Each line shares the load equally and is pre-tensioned, minimizing the amount of rope stretch that will occur in the event of a failure of either line.
Adoption of a Two Tensioned Rope Lower System:
Accomplishing a two tensioned rope lower does not require a prohibitive amount of training. The primary procedure changes to a “usual” untensioned belay line system are:
- Master Attachment Point (MAP)
- Selection of DCD + BCD Combination (or MPD)
- Transition to a Two Tensioned Rope Lower
The transition to a two tensioned rope lower system usually occurs at around 30 metres of rope in service. The lowering operation must be halted to transition the system, and the amount of time this takes must be considered as part of the risk benefit analysis. Transitioning to the two tensioned system on a shorter lower would unnecessarily lengthen the time taken to lower the patient package to the ground, without significantly lessening the risk of ground strike (remember, the amount of rope stretch is proportional to the amount of rope in service).
At height greater than 30 metres, there is a dual benefit to transitioning to a two tensioned rope lower system, as not only do we minimize rope stretch, but we also make the system easier to manage, reducing, and likely eliminating, the number of times that we lock up the belay device and therefore minimizing the amount of time that the patient package is suspended.
The use of the MPD in the system allows us to transition much sooner, as there is no halting of the lowering operation to accomplish a TTRL.
Master Attachment Point (MAP)
The method of patient and rescuer attachment must utilize a MAP to accommodate the distribution of the load between the two ropes. Creating a redundant, master point of attachment for the load allows a combined patient and rescuer tie in. This in turn prevents patient and rescuer separation in the event of the catastrophic failure of either of the ropes. Using a MAP for a single rescuer load allows for greater rescuer comfort, as it allows the rescuer to determine their weight distribution.
Utilizing a single method of attaching rescue loads, with or without a litter (such as when performing pickoffs or line transfers) would simplify training and skills maintenance.
Interlocking long tailed bowlines create a simple, redundant MAP that does not require any hardware, provides two separate attachment tails, and can accommodate a three way pull. It is simple and quick to tie, and is versatile. Use of this knot allows any system to be set up very quickly, as one team member can tie the knot and create the MAP using no hardware and without having to know exactly what will be suspended. The loop created can have multiple attachments clipped into it, and the two long tails can be used for attendant and patient tie-ins. Caution must be taken to ensure clipping of both main and belay line loops to achieve redundancy.
A Rigging ring or rigging plate can also be used for the MAP. The primary drawback of using a rigging ring is the amount of carabiners utilized in attaching the load.
Long tailed interlocking bowlines. This method of MAP allows the tension to be shared or transferred between the main and belay lines without affecting the rescue load below the knot. (Kevin Ristau photo)
Selection of DCD + BCD Combination, & Transition
The MPD can be used as both a BCD that meets the BCDTM and a DCD. In fact, using the MPD simplifies the operation as both lines are mirror images of each other, and transitioning can be accomplished without halting the lowering operation.
The load is first belayed over the edge with an un-tensioned belay line. Once the rescuer is clear of the edge and has control of the load, at approximately 10 metres, the belay line is allowed to come under tension and the operator engages the release handle on the MPD. The load is then lowered equally between the two lines. With two MPD, we can achieve a true mirrored system.
TPB in front of Brake Rack
Probably the most versatile system is where a TPB (with LRH) is added in front of the brake rack on the load line, and a brake rack is added behind the TPB on the belay line. Again, this creates a mirrored system where either line can become the belay line or the load line if there is a need to transition back to a single rope tensioned system.
Operation of the TPB needs to be modified somewhat, as the operator will not be able to create the usual 90 degree bend in the rope due to the tension in the line. Care must be taken to avoid an encircling grip, and operate the prussiks using a “scissored fingers” technique, holding the prussiks back just enough to allow the rope through.
The system is transitioned to a Two Tensioned Rope Lower after the patient and rescuer are clear of the edge and any obstacles. Once the rescuer is comfortable with the line of descent and has control of the load, the system can be transitioned.
The lowering operation is halted and a brake rack is inserted behind the tandem prussik on the belay line. A TPB is added in front of the brake rack on the main line in order to provide a hands free backup to the DCD.
The two ropes are now mirrored, and the lowering operation is continued with the operators simultaneously lowering on both ropes while minding the tandem prussiks. Knot passing and transferring of tension can be accomplished quickly and efficiently as a TPB with Load Releasing Hitch (LRH) is already part of the system on each rope.
The potential for rescues at height is increasing. More high-rise construction also means more high-rise maintenance.
Any organization that has a potential for rope rescues at heights of greater than 30 metres needs to evaluate its systems and select a method to deal with the issues of long lowers. Nobody wants to have a patient hanging in the basket while the rescue team attempts to un-cluster a poor system choice mid-rescue.
The two tensioned rope lower system is far safer and more manageable than a standard two-rope system for long lowers. It has been our experience that the two-tensioned rope system is easily taught and readily accepted by rope rescue personnel.
It is important that we continually re-evaluate our systems to ensure that they are safe, effective, and in line with evolving rope rescue technique.
Gibbs, M and Mauthner, K, (1996), Seminar Notes, Rigging for Rescue
Gibbs, Mike, (2007) Rescue Belays, Important considerations for Long Lowers, Rigging for Rescue, Int. Technical Rescue Symposium
Brown, Mike, (2000), Engineering Practical Rope Rescue Systems,
Lipke, M, (2009), Technical Rescue Riggers Guide, Second Edition,
On Rope, New Revised Edition, by Bruce Smith and Allen Padgett, National Speleological Society,1996
Attachment Disorder, Fire Rescue Magazine, 10/2006, Mark Denvir
CSA Z259.16,Design of active fall-protection systems
NFPA 1006, Standard for Rescue Technician Professional Qualifications
NFPA 1670, Standard on Operations and Training for Technical Search and Rescue Incidents
NFPA 1983, Standard on Fire Service Life Safety Rope and System Components