A mobile scaffold is 24 feet high and 8 feet wide. What is the maximum height-to-base width ratio allowed by OSHA before the scaffold must be tied off or guyed?
Correct Answer
A) 4:1
OSHA 29 CFR 1926.452 allows mobile scaffolds to have a maximum height-to-base width ratio of 4:1. At 24 feet high and 8 feet wide (24÷8=3:1), this scaffold is within limits.
Why This Is the Correct Answer
OSHA 29 CFR 1926.452(w) establishes that mobile scaffolds must maintain a maximum height-to-base width ratio of 4:1 before requiring tie-offs or guy wires. This safety standard prevents scaffold tipping by ensuring adequate base stability. In this example, a 24-foot high scaffold with an 8-foot base has a 3:1 ratio (24÷8=3), which is safely within the 4:1 maximum limit, so no additional stabilization is required.
Why the Other Options Are Wrong
Option B: 6:1
A 6:1 ratio would be dangerously unstable for mobile scaffolds. OSHA specifically limits the ratio to 4:1 because higher ratios create significant tipping hazards. A 6:1 ratio would allow a 48-foot high scaffold on an 8-foot base, which would be extremely unsafe and violate OSHA regulations designed to prevent scaffold collapse and worker injuries.
Option C: 3:1
A 3:1 ratio is actually the current ratio of this scaffold (24÷8=3), not the maximum allowed. While this ratio is safe and compliant, OSHA allows up to 4:1 before requiring tie-offs. Setting the limit at 3:1 would be unnecessarily restrictive and not reflect the actual OSHA standard for mobile scaffold stability.
Option D: 2:1
A 2:1 ratio is overly conservative and not the OSHA standard. This would severely limit scaffold height unnecessarily, reducing productivity without safety justification. OSHA determined through engineering analysis that 4:1 provides adequate stability for mobile scaffolds, making 2:1 an incorrect and impractical limitation that doesn't align with established safety regulations.
Memory Technique
Remember 'Mobile scaffolds: FOUR to the floor' - the 4:1 ratio means for every 4 feet of height, you need 1 foot of base width before tie-offs are required.
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