EN 566 sets the requirements for mountaineering slings. Although written for climbing, slings are widely used in industrial rope access, rescue and arboriculture to build anchor points.
The requirement
Minimum static strength is 22 kN. Slings are made from nylon (polyamide) or Dyneema (HMPE). Dyneema is lighter and thinner but has a low melting point and loses more strength when knotted.
A critical warning
A sling copes badly with dynamic loading — it barely stretches at all. Even a short free fall onto a sling generates over 20 kN, enough to break it or, more dangerously, to injure the worker internally. A sling must always be kept taut, and an energy absorber is essential in any fall arrest system.
Tying a knot in a sling reduces its strength by 30–50%. Running a sling over a sharp edge must likewise be avoided.