Anchors strength and anchors safety
Ancor strength refers to the maximum load the anchor can take without breaking. Anchor strength is never an absolute number, and there's no real way to know it without destructive test (adding and dynamometer and increasing the load until it breaks). Nevertheles, it is essential to estimate the strength, in relation to the expected load it needs to support. For example, for a rope rescue, when hauling is needed, you need a stronger anchor than for rappeling.
Anchor safety is the measure of certainty the anchor will not pull out by chance, or by user mistake. Cmmon examples are a nut that is pulled in the wrong direction, a sling around a spike, that is accidetially lifted or even if you decide to change the direction of pull after the anchor i already set. Anchor safety also refers to the immediate vicinity to the anchor: the rock quality, the rock type etc.
The following table shows a few examples for strong, weak, safe and unsafe anchors:
contributions to this page by: Mica yaniv and others...