You are calculating the load capacity for a mobile crane. The crane chart shows a capacity of 15,000 pounds at a 20-foot radius. If you need to lift a load weighing 12,000 pounds including rigging, what is the safety factor being applied?
Correct Answer
D) 1.25
The safety factor is calculated by dividing the crane capacity by the actual load: 15,000 ÷ 12,000 = 1.25. This provides a 25% safety margin above the actual load weight.
Why This Is the Correct Answer
The safety factor is calculated by dividing the crane's rated capacity by the actual load weight being lifted. In this case, the crane has a capacity of 15,000 pounds at 20-foot radius, and the load weighs 12,000 pounds including rigging. The calculation is 15,000 ÷ 12,000 = 1.25, which means the crane capacity is 1.25 times greater than the load, providing a 25% safety margin.
Why the Other Options Are Wrong
Option A: 1.20
1.15 would result from incorrect calculation or using wrong values. This would only provide a 15% safety margin, which is insufficient for crane operations.
Option B: 1.15
1.20 would result from incorrect calculation. This would only provide a 20% safety margin, which doesn't match the actual relationship between 15,000 and 12,000 pounds.
Option C: 1.33
1.33 would result from reversing the calculation or using incorrect values. This would suggest a 33% safety margin, which while conservative, is not what the given numbers produce.
Memory Technique
Remember 'Big over Little' - the bigger capacity number goes over the littler load number when calculating safety factor.
Reference Hint
Look up crane safety and rigging sections in construction safety manuals or OSHA 1926 Subpart CC - Cranes and Derricks in Construction
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