One of the first lessons we teach to both Level 2’s and Level 3’s is the difference between Safe Working Loads and Working Load Limits.
There is always a lot of confusion over these terms and how they apply to our work in the industrial rope access world.
WLL – Working Load Limit: This is the number marked on a piece of equipment indicating the maximum load that is safe to apply to it. It is a number established by the manufacturer of the item based on its known Minimum Breaking Strength (MBS) to which they will then factor in a margin of safety to get the final number. WLL’s are predominately found on lifting and rigging equipment and not on rope access equipment.
SWL – Safe Working Load: This is a number you will rarely find marked on any equipment. It is a number derived from a formula worked out by a competent person based on the Minimum Breaking Strength of the item. The standard formula is currently 10% of the MBS for items of fabric (tape slings, ropes etc.) and 20% of the MBS for items of metal. Almost all equipment used by the rope access technician is marked only with the MBS.
It is very important to ensure that you are aware of the markings and numbers on all the equipment you are using and their meanings. Confusing an MBS and a WLL and then using the wrong piece of equipment can have serious consequences as was the case in 2014 when a Circus act went terribly wrong. You can read about it by clicking here.