A crane operator is lifting a 15,000-pound load with a crane rated at 25,000 pounds capacity. The load chart shows the crane's capacity at the current boom length and angle is 18,000 pounds. What is the safety factor for this lift?
Correct Answer
A) 1.2:1
The safety factor is calculated by dividing the crane's rated capacity at the working configuration (18,000 lbs) by the actual load weight (15,000 lbs), which equals 1.2:1. While technically within limits, this is a minimal safety margin.
Why This Is the Correct Answer
The safety factor is correctly calculated by dividing the crane's actual capacity at the current configuration (18,000 lbs from the load chart) by the weight of the load being lifted (15,000 lbs). This gives us 18,000 ÷ 15,000 = 1.2, expressed as a ratio of 1.2:1. The key is using the load chart capacity for the specific boom configuration, not the crane's maximum rated capacity.
Why the Other Options Are Wrong
Option B: 1.5:1
This would result from incorrectly dividing 22,500 by 15,000, which doesn't correspond to any relevant capacity figure in the problem. The 1.5:1 ratio is not supported by the given data.
Option C: 1.67:1
This would result from incorrectly dividing the crane's maximum capacity (25,000 lbs) by the load weight (15,000 lbs), giving 1.67:1. However, safety factor calculations must use the crane's capacity at the actual working configuration, not its maximum capacity.
Option D: This lift exceeds safe working limits
The lift does not exceed safe working limits since the 15,000-pound load is less than the 18,000-pound capacity shown on the load chart for the current boom configuration. The lift is technically safe, though with minimal margin.
Memory Technique
Remember 'Chart Capacity over Current Load' - always use the load chart capacity (not max capacity) divided by the actual load weight for safety factor calculations.
Reference Hint
Look up crane safety and rigging calculations in Chapter 15 (Construction Safety) or crane operation sections of your contractor reference manual.
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