A mobile scaffold is 20 feet high and 6 feet wide. What is the maximum height-to-base width ratio allowed by OSHA before outriggers are required?
Correct Answer
A) 4:1
OSHA 1926.452(w) limits mobile scaffolds to a height-to-base width ratio of 4:1. At 20 feet high and 6 feet wide (20:6 = 3.33:1), this scaffold meets requirements without outriggers.
Why This Is the Correct Answer
OSHA 29 CFR 1926.452(w)(6) limits mobile scaffolds to a maximum height-to-base width ratio of 4:1. Beyond this ratio, the scaffold becomes unstable and outriggers or stabilizers must be added. The scaffold in the question (20:6 = 3.33:1) is within the 4:1 limit and does not require outriggers.
Why the Other Options Are Wrong
Option B: 5:1
5:1 exceeds the OSHA-permitted ratio. A 5:1 ratio would allow taller, less stable configurations without outriggers, which is prohibited. This answer reflects a common error of confusing mobile scaffold limits with other scaffold types.
Option C: 3:1
3:1 is more conservative than the OSHA requirement and would unnecessarily restrict scaffold use. While a 3:1 ratio is safer, OSHA's published standard permits up to 4:1 before outriggers are required.
Option D: 2:1
2:1 is far too restrictive. It would make most mobile scaffolds impractical and does not correspond to any OSHA standard for mobile scaffolding height-to-base ratios.
Memory Technique
Remember: Mobile scaffold = 4:1 max. Picture a scaffold that is 4 times taller than it is wide — beyond that it tips over without outriggers. The number '4' appears in both mobile scaffold and ladder placement rules, so link them: both use 4 for stability.
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