Safe Working Load (SWL) sometimes stated as the Normal Working Load (NWL) is the maximum safe

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

that a piece of

lifting equipment Lifting equipment, also known as lifting gear, is a general term for any equipment that can be used to lift and lower loads. Types of lifting equipment include heavy machinery such as the patient lift, overhead cranes, forklifts, jacks, building ...

, lifting device or accessory can exert to lift, suspend, or lower, a given

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

without fear of breaking. Usually marked on the equipment by the manufacturer. It is a calculation of the Minimum Breaking Strength (MBS) also known as Minimum Breaking Load (MBL) divided by a safety factor, usually ranging from 4 to 6 on lifting equipment. The factor can be as high as 10:1 or 10 to 1, if the equipment poses a risk to a person's life. Working Load Limit (WLL) is the maximum working load designed by the manufacturer. This load represents a

that is much less than that required to make the lifting equipment fail or yield. The WLL is calculated by dividing MBL by a

safety factor In engineering, a factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load. Safety factors are often calculated using detailed analy ...

(SF). An example of this would be a chain that has a MBL of 2000

lbf The pound of force or pound-force (symbol: lbf, sometimes lbf,) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system. Pound-force should not be confused with pound-m ...

(8.89 kN) would have a SWL or WLL of 400 lbf (1.78 kN) if a safety factor of 5 (5:1, 5 to 1, or 1/5) is used. The current American standard for lifting and handling devices is Reference (1), which provides minimum structural and mechanical design and electrical component selection criteria for ASME B30.20 below-the-hook lifting devices. The provisions in this Standard apply to the design or modification of below-the-hook lifting devices. As such: WLL = MBL / SF SWL is no longer used to identify the maximum capacity of equipment due to it being too vague and leaving it open for legal issues. The US and European standards switched to The Working Load Limit' standard shortly after.

References

{{reflist Safety engineering 1) ASME BTH-1 (Below the Hook Lifting Devices)