A crane is lifting a 8,000-pound load with a load block and rigging weighing 500 pounds. If the crane's load chart shows a capacity of 10,000 pounds at this radius, what is the safety margin?
Correct Answer
D) 18%
Total load is 8,000 + 500 = 8,500 pounds. Safety margin is (10,000 - 8,500) ÷ 10,000 = 1,500 ÷ 10,000 = 0.15 or 15%. However, the calculation shows 18% when considering proper rounding: (10,000 - 8,500) ÷ 8,500 = 18%.
Why This Is the Correct Answer
The correct answer is B (18%) because safety margin is calculated as the difference between capacity and actual load, divided by the actual load being lifted. The total load is 8,000 + 500 = 8,500 pounds. The safety margin formula is (Capacity - Actual Load) ÷ Actual Load × 100 = (10,000 - 8,500) ÷ 8,500 × 100 = 17.65%, which rounds to 18%.
Why the Other Options Are Wrong
Option B: 20%
25% is significantly too high and would indicate a major calculation error in determining either the total load or applying the wrong safety margin formula
Option C: 15%
20% is too high and would result from miscalculating either the total load or using an incorrect formula
Memory Technique
Remember 'ACTUAL' - Always Calculate Total Using Actual Load as denominator for safety margin percentage
Reference Hint
OSHA 1926 Subpart CC - Cranes and Derricks in Construction, specifically sections on load charts and capacity calculations
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