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The key to lifting a maximum capacity load with a mobile crane is the outriggers. They provide a solid platform for the crane's safe operation and efficient use. Operators and workers within a crane's radius must always be aware of how critical the placement and use of outriggers are to the crane's performance. Without this awareness they may place both themselves and the crane in peril.
Statistics show that at least 50% of crane incidents occur because the mobile crane or outriggers are not set-up properly. Specific hazards that can cause or contribute to failure or collapse include:
Use The Correct Load Chart: The purpose of outriggers is to improve the stability of the crane. Accurate use of the "on-outriggers fully extended" load chart, requires that outriggers be fully extended and they must bring the rig completely off-rubber. If the tires are touching the ground, then the "on-rubber" load chart is the only one that can be used. Manufacturers do not recommend extending only one or two of the outriggers. If outriggers are to be used, fully extend all of them and get the tires off the ground. Accidents commonly occur because the operator is lifting from only one side of the rig, with only two outriggers extended. Then, later in the day, this same operator is asked to swing the boom to the other side of the rig for a pick. He does this without thinking and topples the crane. (Note: The load charts of some manufacturers now permit partially-extended outriggers, so always refer to the correct load chart prior to making the lift.)
Outrigger Pads and Floats: The pads found on all crane outriggers are designed for good ground conditions. Poor conditions reduce the amount of load a crane can safely place on the outrigger pad. Because of this, many crane operations require additional support or "floats." Supplemental floats are made of substantial material and must always be larger than the outrigger pad. These floats disperse the weight of the crane and its load over more ground area than does the pad. Any float or cribbing which is smaller than the pad, actually increases the pressure placed on the ground. This increase in pressure, particularly in poor ground conditions, can cause an outrigger to "punch through," and bring about an accident.
Leveling: Also be aware that all floats and cribbing must be level. If the outrigger pad is set down on an unleveled float, the outrigger pad may slide off when under load, causing the crane to tip. Many manufacturers stipulate that the crane must be within 1% of level before their load chart applies. In a 20-foot span this is only 2 inches off-level! Past this point, the crane can lose 15% - 20% or more of its rated capacity. So, keep the crane on solid level footing.
Operators and workers must never take a mobile crane for granted. Plan the work--setting up the crane safely every time, for every lift!
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