Sling force calculation - FoS of 4 taken into account of rigging?

[Kiri Robbie]

Your sling force calculation showed a 32t live load on a spreader with unequal slings to calculate / determine size of a shackle; does the 32t weight need to factor in a FoS of 4, or is the FoS of 4 already taken into account of the rigging?

[Florian Dieterle]

As a general comment, equipment that is intended for lifting, already has the necessary safety factors, so on a vertical lift, a 1 ton load can be lifted with a 1 ton shackle. The proprietary produce suppliers then publish reduction factors for different configurations (e.g. side loaded shackles, choked slings, etc). Because these are items that are for general purpose, re-used and have various local effects, the safety factor is high and as mentioned above, around FoS 4. 

Custom designed elements such as steel lugs are then designed to the relevant standards with the appropriate load factors and material factors. Special consideration to be given to lateral loading (out-of-plane) and dynamic effects due to jerky movement and emergency braking.