Scaffolding planks must extend over their support a minimum of 6 inches but not more than:
Correct Answer
B) 18 inches
OSHA requires scaffold planks to extend over supports a minimum of 6 inches but not more than 18 inches to prevent tipping or excessive deflection.
Why This Is the Correct Answer
OSHA 29 CFR 1926.451(b)(1) requires scaffold planks to extend beyond their end supports a minimum of 6 inches and a maximum of 18 inches. This prevents two dangers: too little overhang (plank slides off support) and too much overhang (plank tips under worker's weight — a cantilever effect).
Why the Other Options Are Wrong
Option A: 12 inches
12 inches is less than the 18-inch maximum allowed by OSHA. While 12 inches is within the acceptable range, the question asks for the maximum allowed — which is 18 inches, not 12.
Option C: 30 inches
30 inches far exceeds the OSHA maximum. An overhang of 30 inches would create significant tip-over risk, acting as a cantilever that could launch a worker off the scaffold if they step near the end.
Option D: 24 inches
24 inches also exceeds the 18-inch OSHA maximum. This is a common wrong answer because 24 inches (2 feet) is a round number that seems reasonable, but OSHA specifically limits overhang to 18 inches.
Memory Technique
Remember '6 to 18' as a phone area code: scaffold planks live between 6 and 18 inches of overhang. Or think of a ruler: 6 inches is half a foot (minimum), 18 inches is one and a half feet (maximum). No more, no less.
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