Safe Working Load (SWL) is typically determined by dividing the MBS of a carabiner by the Safety Factor (SF) required for a particular use. As stated above it is possible that an entertainment rigger may calculate a different SWL for a particular use of a carabiner than the value determined by a rescue technician.
SWL is determined by industry standards unlike WLL which is set by manufacturer.
SWL calculation example
A particular steel carabiner has a long-axis 3σ MBS of 50kN. The manufacturer has specified a DF of 4 for this connector, regardless of use.
This carabiner has a WLL of 12.5kN and this value should never be exceeded in normal use – regardless of industry or application. If this value is exceeded, it should not fail below the MBS however it should then be removed from service and destroyed.
An entertainment rigger, working in a certain country is required by the industry code-of- practice to use a SF of 10 for flying performers and thus determines the SWL of this carabiner is 5kN (50kN/10).
A rescue technician in another country is supposed to apply a SF of 5 to hardware and thus determines a SWL = 10kN (50kN/5) for an identical connector.