Every bit of lift equipment comes with a tag or a stamp featuring a certain number. This number is critical to the equipment’s safety and functionality, but doesn’t get the attention is ought to.
Practically speaking, the terms Safe Working Load and Working Load Limit are interchangeable. Both terms refer to the limit of weight the equipment is designed to safely lift under normal conditions. Breaking Load (or Minimum Breaking Force), is the weight at which the equipment would fail a test. The distance between the Safe Working Load and the Breaking Load accounts for the Safety Margin. This distance is left to account for equipment that may experience wear and tear, damage, and unexpected and unpredictable events that could occur in a work environment.
Instead of being a single absolute figure, that margin tends to vary by equipment type, and is mostly stated as a design factor concerning equipment type. Chain slings are made to a factor of roughly 4:1, meaning that the breaking load is four times the rated working load. In comparison, shackles are generally rated to a factor of 6:1. This is due to the fact that shackles can easily be misused or loaded at an angle whereas a chain is running more or less straight. The objective is not to memorise every figure, but rather to appreciate the fact that the number on the tag does allow for some buffer, and that margin does exist to be a backup, and not an invitation for a load that is closer to the breaking point of the limit indicated on the tag.
There are several factors that limit the working load limit, which comprises the lift angle. Consider a one tonne sling doing a vertical lift. It is rated for the full one tonne limit under that vertical condition. If that one tonne sling were to be used with a fifty degree spread, that one tonne limit is no longer valid, and the load in each leg of the sling actually increases as the spread angle increases. The same principle applies to multi-legged slings. Adding more legs to a multi-leg sling does not necessarily mean a higher load limit. Because the angle of the lift dictates how much each leg will carry, most manufacturers will provide a multi-leg derating chart to help avoid having to calculate the limits at the worksite. Items such as temperature and wear, including any visible damage further reduce the safe working limit. Therefore, if a piece of equipment shows signs of hard use but has a tag that still displays the original safe working limit, it should not be trusted at face value.
A color code system is used to quickly show the status of the equipment, most of the time signifying the equipment has passed the minimum inspection period and is safe to use. Most often, the color code system shows inspection status and not the equipment load rating. It allows anyone on site to quickly determine whether a piece of equipment has passed its inspection period. Of course, like all color codes, the system is useful, but it should not become a substitute for checking the equipment’s safe limit and load rating prior to use for a specific lift.
If an equipment tag is absent, damaged, or difficult to read, guesswork is not an option. Equipment without a tag is not a blank space to populate with your assumptions. It is equipment stating it is not safe to use, possibly in an even more expensive load. The rating on the tag is critical information for the usability of the piece of equipment. It is more important than the brand, price, and freshness of the piece of equipment. It is imperative this rating is checked before the equipment is in use, not in hindsight after an avoidable incident.