Don't know if this will help you further, but below is a definition of the term "two-blocking"; it appears there is no German term for the occurrence, and it should be described as "Zusammenzug der Seilrolle und des Flaschenzugs" o.Ä.

"Two-blocking" is colloquial expression meaning that the two blocks are drawn together, as described below.

The safety device is just a limit switch.

http://journals.iranscience.net:800/Default/www.asme.org/cns...

Two of the primary causes of load drops identified by the NRC research in conjunction with RG 1.104 are severe types of overloads known as “two blocking” and “load hangup”. Two blocking occurs when control malfunction or maintenance error permits unintentional overhoisting, resulting in solid contact between the hook block and the head block or its supporting structure. The typical consequence is immediate failure of the wire rope and dropping the load or empty hook block. Load hangup is abrupt snagging of the moving load, resulting in similarly severe effects on the equipment. Other causes of dropped loads include “mis-reeving” of the hoist wire rope and failure of the hoisting machinery itself.