If we load the crane beyond the manufacturer's ratings - even in a stability-limited area of the rating chart - we have no idea which structural components may be overloaded before the crane actually shows signs of tipping.Ī chart may list a rating of 5,000 pounds limited by stability. These are not ratings which will tip the crane! They are only a certain percentage of the load at which the crane will tip. It only indicates that no structural limitations are exceeded by the stability ratings shown on the chart.
However, the rating chart does not tell us that it is safe for the crane to approach tipping without suffering structural consequences. Who cannot imagine the potential disaster of a structural failure? Most operators agree - you don't cheat on structural limitations. Their further requirements also state, "When loads which are limited by structural competence rather than by stability are to be handled, it shall be ascertained that the weight of the load has been determined within 10 percent before it is lifted." OSHA clearly recognizes the importance of structural limits. US-OSHA (Occupational Safety and Health Administration) requires that, "When ratings are limited by structural competence, such ratings shall be clearly shown and emphasized on the rating charts." There can be no doubt that the intent here is to alert crane operators to the structural limitations for their cranes. Rather, it would seem that many users are guilty of trying to second guess the crane manufacturer. In over 25 years in the crane and rigging industry, I have heard the above "logic" too many times to believe it constitutes an isolated misunderstanding. Sound familiar? - Believe it's true? - It absolutely is not!īy relying on tipping to signal a problem, an operator can overload a crane's structural components by a tremendous amount. The weight was over the chart, but we were in a tipping range, so I knew she'd get light before anything would break." How many times have you heard a conversation like this? "We had a heavy piece to lift. Beyond this point, however, a frightening number of users mistakenly read dangerous misinformation into the chart. This information is clearly indicated in some fashion on all rating charts. While some charts can be very complex, most crane users understand that a chart divides rated capacities into two general categories: (l) those limited by tipping (stability) and (2) those limited by structural factors. The rating chart for a mobile crane spells out operating parameters which are critical to the machine's safe use. Operating in the Twilight Zone of Crane Capacities This article was published in the November 1994 issue of Lifting & Transportation International Magazine. International rigging, lift supervision, rigging quizzes, rigging training, rigging book sales, Design of rigging software, rigging engineering, erection, guy derrick analysis,
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