Shock Loading from a Sudden Stop
You are using a 2-ton chain hoist to lift a 3,000 lb load. The load is lifted 5 feet and then the operator suddenly stops the hoist, causing the load to swing. The hoist is mounted on a trolley. The load is attached with a single vertical chain sling. The chain sling has a rated capacity of 3.5 tons in vertical hitch. The hoist and trolley are rated for 2 tons.
1. What hazards are present in this situation?
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The load weight of 3,000 lb (1.5 tons) is within the hoist's 2-ton capacity, but the sudden stop introduces shock loading. Shock loading can increase the effective load on the hoist, trolley, and sling by a factor of 2 or more. The hoist and trolley may be overloaded dynamically. The swinging load creates side loading on the hoist and trolley, which can cause the trolley to move or the load to swing into personnel. The chain sling, rated 3.5 tons, may still be adequate if shock factor is less than 2.33, but the hoist is at risk. Additionally, the load may shift if the sling is not centered.
2. How can you reduce the risk of shock loading?
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Operate the hoist smoothly, avoiding sudden starts and stops. Use a soft start and stop, and keep the load under control with tag lines. Ensure the load is balanced and the sling is vertical. Do not exceed the hoist's rated capacity; consider the dynamic loads. If the load must be stopped suddenly, the hoist should be de-rated. In this case, the hoist is only 2 tons, and the load is 1.5 tons, so there is some margin, but shock loading could exceed 2 tons. Therefore, the operator should be trained to avoid shock loading. Also, inspect the hoist and trolley for damage.