Safe Working Load (SWL) and Working Load Limit (WLL) are terms used in the lifting industry to indicate the maximum loads lifting equipment can lift without breaking.
Read on to find out the difference between the two.
Safe Working Load (SWL)
SWL indicates the amount of force/weight/mass that a piece of lifting equipment can withstand without breaking when lifting items.
Lifting equipment refers to any item used to lift products in the workplace, whether it’s lifting accessories, like slings or shackles, or machinery, like cranes or forklifts, to give some examples.
SWL is outdated. Manufacturers tend not to use the term these days. It can be misleading.
Why is SWL not used anymore?
The term Safe Working Load (SWL) isn’t used by manufacturers anymore, because it could be construed that ‘any’ load within the SWL limit is safe to lift. But the reality is, there are certain factors that determine the rated capacity of the item being used.
One of them being the configuration. For example, the rating of a sling is for a lone sling being used in a vertical position (a straight pull). But what happens if a choke hitch is used with the sling? Then 20% needs to be reduced from the rated capacity. Or what if two or more slings are used to lift the load?
In these types of cases, mode factors come into the equation. Oftentimes, ‘equation’ is the operative word, because the slinger, or whatever trained person is doing the lift, has to figure out which accessories, with the suitable rating in the right configuration, to use. They do this using the Uniform Load Method.
On another note, because of legal implications, USA stopped using SWL in the early 1990s. Later, European and ISO Standards also ceased to use the term. But it took until around the year 2000 for a suitable universal replacement to be established. It was decided that WLL would be used to describe the lifting capacities of accessories. However, people still sometimes use the term Safe Working. Hence the frequent confusion.
For lifting machinery like winches, hoists, and cranes, Safe Working Load was replaced by Rated Capacity.
Rated Capacity is the maximum gross weight that can be lifted by lifting machinery in specific configurations.
The scenario is similar to Safe Load Indicator (SLI) vs Rated Capacity Indictor (RCI). A Rated Capacity Indictor is a system in cranes that gives readings to operators and prevents the crane from lifting more than its manufacturer’s guidelines.
SLI used to be the official term, but RCI is now favoured. This is because the system can only inform the operator what the crane is capable of lifting in the specified configuration.
Similarly to Safe Working Load, Safe Load Indicator can be misleading by implying that equipment is safe to use in any configuration.
Working Load Limit (WLL)
According to LEEA, WLL is ‘The maximum load (mass) that an item of lifting equipment is designed to raise, lower, or suspend.’
WLL replaced the misleading SWL by, instead of implying that the piece of equipment is safe to lift in any configuration, it indicates the maximum load the equipment can lift. Hence, the word ‘limit’.
Working Load Limit should be used for all lifting equipment below the crane’s hook block.
Who decides the load capacity for lifting equipment?
The WLL of lifting equipment is set by the equipment’s manufacturer. The manufacturer rates the accessory by measuring the amount of force it would take to break the accessory. By European standards, the minimum safety factor of a new textile sling is 7:1. Which means, when new, a sling with a 2t WLL, for example, must be able to lift a load of at least 14t before breakage.
The 2t sling in question is only good for 2t in the vertical position (straight pull). A 3t sling is only capable of lifting a load of up to 3t, and so on.
This factor of safety only really applies to new accessories. Things like wear and tear, age, knots, tears, exposure to sunlight, and cuts, etc, can affect it.
To summarise
- Safe Working Load (SWL) indicates the amount of force/weight/mass that a piece of lifting equipment can withstand without breaking when lifting items.
- The term SWL is now unfavoured by manufacturers. It has been replaced with WLL.
- Working Load Limit (WLL) is the maximum weight that lifting equipment can lift in any configuration.
- The rating of lifting equipment is determined by the manufacturer of such equipment.
- Working Load Limit should be used for all lifting equipment below the crane’s hook block.
- When using lifting equipment in any way that does not allow its maximum rated capacity, assessments should be done by a competent person, such as a slinger, crane supervisor, or appointed person, in order to derate the accessory to suit the configuration per lift.
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