The tear-webbing inside a via ferrata set that decelerates a fall into the steel cable. To EN 958:2017 it keeps impact force under 6 kN at 120 kg — and is scrap afterwards.
On a via ferrata you're clipped to a rigid steel cable, not a stretchy climbing rope — a fall there can reach fall factor 5, far beyond the 2 you see in sport climbing. The shock absorber is the only component that swallows that energy. Three hard rules follow. First, there is no improvised version: a sling without an absorber is not a belay, and old friction brakes count as obsolete. Second, the absorber only works if you stay close to the last anchor; climbing well past it lengthens the fall. Third, it is single-use — after any real fall the set gets replaced, even if it looks untouched. For children, the certification also carries a lower weight limit of around 40 kg; below that, an additional short-rope belay is required.