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Safe Working Load (SWL) is a term used in conjunction with lifting appliances in the construction industry.

The term is most commonly used with:

SWL is the maximum load you can apply to a item and be certain that it won't fail. A factor of safety is always applied onto this load to ensure safe handling of the load.

The reason to have such a term inprinted on all equipment has to do with Rules and Regulations - but most of all with Insurance coverage. If you can prove that you used proper rigging, then that is one less question the lawyers can ask when things go wrong :)

The factor of safety depends on the type of equipment, and it's frequency and style of use.

For single lift items (hookup points on items that are to be abandoned on the seabed for instance) the factor of safety is low (approx 1.5)- the operation will most of the time be performed in a controlled and efficient manner, and only once.

For cranes and other items that are very expensive, the factor of safety is a bit higher (approx 2). Because of the cost involved to replace the item, it is going to be used in a careful manner.

Hooks, Shackles, Steel Wire Rope and other connection equipment are rated a bit higher (approx 5). They can be used again and again with much wear and tear. Though they are regularly inspected, they are prone to misuse.

Syntetic Fibre Rope often has the highest factor of safety (often in excess of 7). This is because it's very vulnerable to the environment it's used in - the rope takes damage from mud and UV-radiation and it's easily severed on sharp edges. Fibre ropes also give no indication of failure prior to complete fracture, quite the opposite of steel hooks and shackles who will deform a great deal prior to ultimate failure.

SWL is in some countries superseeded by Working Load Limit - the name changes, but the background is the same.

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