18.5.5 Working Load Limit

Unlike other lifting equipment, the working load limit of fibre rope slings is not calculated by the application of a simple factor of safety. It is calculated from the specified breaking load of a single rope less a 10% allowance for the splice efficiency to which the factor of safety (coefficient of utilisation) is applied, i.e. 90% of specified breaking load divided by factor of safety. The resultant is then multiplied by an assembly factor to arrive at the WLL of a particular sling assembly.

The assembly factor takes the multiplicity of parts into account to determine the WLL of the sling assembly. For single and endless slings, this assumes the sling to be in a straight pull and for two leg, three leg and four leg slings it assumes the legs will be disposed at a maximum angle of 45° to the vertical (90° included angle) as shown in #id-d0c030fb-dd65-4a57-e9f8-97521b6e66e8__id-c0907720-ad6d-4851-8ec7-7bcc0f545e07.

The SWL marked on the sling is the maximum load which the sling may lift, in straight pull for single and endless slings or with the legs disposed at a maximum of 45° to the vertical (90° included angle) for two leg, three leg and four leg slings and this must never be exceeded. In many cases, this will be the same as the WLL though, when a sling is to be used in adverse conditions or other circumstances where the Competent Person deems an increased reduction factor is desirable, it may be lower than the maximum SWL.