A crane with a 100-ton capacity is lifting a 75-ton load with a 20-foot boom radius. The load chart shows 80-ton capacity at this radius. What is the safety factor?
Correct Answer
D) 1.07
Safety factor = Rated capacity ÷ Actual load = 80 tons ÷ 75 tons = 1.07. This is below the recommended safety factor of 1.25 for crane operations, indicating the lift is at the edge of safe operating parameters.
Why This Is the Correct Answer
The safety factor is calculated by dividing the rated capacity at the specific boom radius by the actual load being lifted. At a 20-foot boom radius, the load chart shows the crane's capacity is 80 tons, not the maximum 100-ton capacity. Dividing 80 tons by the 75-ton actual load gives 1.07. This calculation uses the correct capacity figure from the load chart rather than the crane's maximum capacity.
Why the Other Options Are Wrong
Option B: Insufficient information
This appears to be a calculation error, possibly dividing 100 tons by 75 tons, which incorrectly uses the crane's maximum capacity instead of the load chart capacity at the 20-foot radius. The boom radius significantly affects lifting capacity.
Option C: 1.33
All necessary information is provided: the actual load (75 tons), the boom radius (20 feet), and the corresponding load chart capacity (80 tons). These three pieces of information are sufficient to calculate the safety factor.
Memory Technique
Remember 'Chart over Carried' - always use the load Chart capacity Over the load being Carried to find safety factor, not the maximum crane capacity.
Reference Hint
Look up crane safety and load chart interpretation in the OSHA Construction Standards (29 CFR 1926 Subpart CC) or crane operation sections of construction safety manuals.
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