Recently, an operator of an overhead crane had been using a chain sling attached to the hook of a crane and was setting it up into a single choker hitch to pick up and turn over a steel frame that was lying horizontally on two sawhorses.

The hook on the sling did not have a safety latch. 

According to ASME B30.10, a latch is a mechanical device used to close the throat opening of a hook.

The purpose of the latch is simply to reduce the possibility of the rigging becoming detached from the hook, primarily in slack conditions. The use of a hook with a latch does not preclude the inadvertent detachment of a slack sling or a load from the hook.

Tilt-up is a method of construction whereby large concrete panels are cast on-site and then raised into position with a crane. The building system, which was conceptualized in the early 1900s, is used throughout North America and across the globe. It is employed on virtually every building type, from distribution centers, to schools, churches, libraries, retail centers, and office buildings.