Single Rope Technique (SRT) is a set of methods used to descend and ascend on the same single rope. SRT is used in caving, potholing, rock climbing, canyoning, roped access for building maintenance and by arborists for tree climbing.
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In the 1930s, as caving became increasingly popular in France, several clubs in the Alps made vertical cave exploration an outdoor sport. During WWII, such a team composed of Pierre Chevalier, Fernand Petzl, Charles Petit-Didier and others explored the Dent de Crolles cave system near Grenoble, France which became the deepest explored cave in the world (-658m) at that time. The lack of available equipment during the war forced Pierre Chevalier and the rest of the team to develop their own equipment, leading to technical innovation. The first use of single rope technique with prusik and mechanical rope-ascenders (Henri Brenot's "monkeys", first used by Chevalier and Brenot in a cave in 1934) can be directly traced back to the exploration of the Dent de Crolles cave system. American caver Bill Cuddington, known as "Vertical Bill" developed in US the single rope techniques (SRT) in the late 1950s. In 1958, two Swiss alpinists, Juesi and Marti teamed together, creating the first commercially-available rope ascender known as the Jumar. In 1968 Bruno Dressler asked Petzl, who worked as a metals machinist, to build a rope-ascending tool, today known as the Petzl Croll, that he had developed by adapting the Jumar to the specificity of Pit caving. Pursuing these developments, Fernand Petzl started in the 1970s a small caving equipment manufacturing company Petzl, which is today a world leader in equipment for both caving, climbing, mountaineering and at-height safety in civil engineering. The development of the rappel rack and the evolution of mechanical ascension systems, notably helped extend the practice and safety of pit exploration to a larger venue of established cavers.
For ascent (prusiking or "jugging"), cammed devices (ascenders, Jumar, Petzl Croll) are used that can be pushed up the rope but that lock and hold the user's weight when a downward force is applied; these must also be easily removable from the rope without being detached from the user. Knots such as the Prusik, Bachmann and Klemheist are used to ascend ropes in emergencies in climbing and mountaineering; they have ceased to be the primary ascent method in SRT because they are slow in use, and ice or mud greatly reduce their efficiency.
Numerous prusik systems have been devised. Popular systems are:
Descent (abseiling or rappeling) uses various forms of friction brake to control speed. The most commonly used are the Petzl Stop (self-locking) and Bobbin, and rappel racks. For safe SRT, especially on drops with complex rigging with intermediate belays, it is essential that the abseiling device can be removed from the rope without being unclipped from the harness. Modern SRT uses specialised devices for both descent and ascent, and low-stretch kernmantel rope of 8 mm-11 mm diameter. Other essential items of a personal SRT set are a sit harness and one or more safety cords ("cows-tails") terminated in carabiners, for temporary attachment to safety ropes at the heads of drops and used in manoeuvres at intermediate rope belays.
How the rope is sent down a shaft has great bearing on the type of SRT used. In general, while rope-walking techniques may be very effective for climbing long unobstructed pitches, they prove less versatile in cases of awkward passages and complex rope rigging with rebelays used to avoid hazards such as loose rocks, waterfalls, and rope damage from rub points.
Rigging in the southeastern USA is done from a single anchor point and pitches are rigged as a single large drop, often in excess of 100m. The rope is usually a thick abrasion resistant type and this allows the rope to go over the lip of a shaft in contact with the rock. This is sometimes pejoratively called Indestructible Rope Technique. To descend such large drops on a bobbin type descender would be difficult owing to the thickness and stiffness of the rope, and the resulting descent would be slow and jerky. The descender could also overheat and melt the surface of the rope. Since racks have a much larger heat sink capacity and offer a much smoother descent on such pitches they are preferred. To ascend the long pitch would be time consuming using the frog system so the rope walking system is preferred.
In Europe pitches are often more difficult and complex multi-pitch rigging is almost universal. Long drops are broken up into smaller pitches by rebelays and deviations are often used to direct the rope away from areas of sharp rock and from water. Where rope rub cannot be avoided rope protectors are installed. Traverses are often installed to allow the rigger to reach an area where it is possible to hang the rope with no rub. Since allowing the rope to rub against the walls is prevented lighter ropes are used, usually 8-9mm thick. This has the advantage of being lighter and therefore more economical to carry on long or deep trips. Bobbin descenders are quicker to change over at rebelays and are also lighter to carry. Rope-walking techniques are less effective in cases of awkward passageway and for changeovers at rebelays.