EN 12841 sets the requirements for the devices that move along the ropes in a rope-access system. The system is built on the two-rope principle: the working line carries the worker's weight, while the safety line is an independent back-up.
The three types
| Type | Function | On which rope |
|---|---|---|
| Type A | Back-up device — follows the rope freely and locks in a fall | Safety line |
| Type B | Ascender — moves up the rope and locks downward | Working line |
| Type C | Descender — provides controlled descent | Working line |
The two-rope principle
The safety of rope access rests entirely on this principle: the failure of one line — a cut rope, a device malfunction, an anchor failure — must never result in a fall. Each rope must have its own independent anchor.
The rope must be EN 1891 type A low-stretch kernmantel. Devices are certified for a specific rope diameter (usually 10–11 mm) — on any other diameter their performance is not guaranteed.