Safe working load is sometimes stated as the Normal Working Load (NWL). It is the maximum safe force that a piece of lifting equipment, lifting device or accessory can exert to lift, suspend, or lower a given mass without fear of breaking.
In simple terms, safe working load of any lifting equipment or lifting accessories is the maximum weight of a load it can carry at any given time safely.
In Health and Safety, it is expected that all manufacturers of a lifting equipment and lifting accessories should specify the safe working load of that equipment/accessory to prevent overload. Overload of an equipment can result to accidental release of the load or toppling of the lifting equipment which could cause serious injury or death.
To ensure safe lifting, risk assessment must be carried out for all lifting exercises. One of the things to consider during the risk assessment is the lifting machinery, lifting accessories and the load.
This consideration will guide on the choice of the best lifting machinery and accessories for a successful completion of the task.
Any machinery that do not have its safe working load conspicuously stamped on the body of the equipment should not be used for lifting based on assumption. If need arise to make use of the equipment, the manufacturer of the lifting equipment or the lifting accessories should be contacted in order to ascertain the capacity of the equipment or accessories before use.
How to calculate safe working load (SWL)
The SWL is determined by dividing the minimum breaking strength (MBS) of a component by a safety factor assigned to that type and use of equipment. The safety factor generally ranges from 4 to 6 unless a failure of the equipment could pose a risk to life; in that instance the safety factor would be a 10.
For example, if a line has an MBS of 1,000 pounds and a safety factor of 5, then the SWL would be 200 pounds. 1000 / 5 = 200. Also called working load limit (WLL).
NOTE: 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.
What Is Working Load Limit
According to wikipedia;
Working Load Limit (WLL) is the maximum working load designed by the manufacturer. This load represents a force 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 (SF). An example of this would be a chain that has a MBL of 2000 lbf (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.