SWL

Dear Readers,

On a construction site, you may often notice SWL warning messages on lifting tools and tackle. SWL stands for Safe Working Load. Understanding key terms like Safe Working Load (SWL) and Working Load Limit (WLL) is important for ensuring safety, efficiency, and adherence to best practices in material handling.

SWL is very important and essential for rigging & hoisting works during construction activities, and sometimes stated as the Normal Working Load (NWL). 

It’s the mass or force that lifting equipment, a device, or an accessory can safely handle to lift, hold, or lower a load without the risk of breaking. This is usually marked on the equipment by the manufacturer and is often set at 1/5 of the Minimum Breaking Strength (MBS), though other fractions like 1/4, 1/6, or 1/10 may also be used.

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 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.  

Thumb Rule for Determination of SWL of Wire Rope Slings:

SWL = 8*D2; in Tons; Where D diameter of the rope in inches.

Example: 

    1 Inch diameter rope 1*1*8 = 8 Tons 

    ½ inch diameter rope 0.5*0.5*8 = 2 Tons

Another way to calculate the SWL of any wire rope is by 

    1. Obtained the Breaking strength of the wire rope as per the class.

    2. Consider the Safety factor (Generally taken as 5 for wire rope, except taken as 10 when used for lifting a person)

    3. Divided the breaking Strength by the factor of safety.

Whether you’re an experienced engineer, a safety officer, or just starting out in the industry, understanding these concepts can make a big difference in creating a safer workplace.