Four-Tier Frame Scaffold on a Gusty Morning
An eight-person masonry crew is erecting a four-tier frame scaffold on the west face of a three-story building. The top platform sits 28 ft above grade on a 6 ft wide base. Two legs bear on 6x6 timber sills; the other two rest on 4-inch concrete block. The top platform is fully planked but was set 18 in from the wall to clear a brick ledge. A guardrail with a 42-inch top rail and a midrail is in place on the three building sides; the street side, where the masons wheel their mortar boards, has no guardrail at all. Two ties connect the scaffold to the building on the east face; the other three faces are untied. Bricklayers climb the cross braces to reach the top. At 11:00 a.m. a gust front arrives with sustained 25 mph wind and 40 mph gusts.
1. Which conditions are violations, and how would you rank them by the risk they create this morning?
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Highest - restraint from tipping, combined with wind. The tower is 28 ft tall on a 6-ft base, roughly a 4.7:1 height-to-base ratio, and only one face is tied. A supported scaffold must be restrained from tipping by guying, tying, bracing, or equivalent, and a tower this tall and this narrow that is untied on three faces is the classic collapse scenario. Add 40-mph gusts and this is the condition that kills people, not injures them.
High - missing guardrail on the working face. The street side is where the masons actually work with mortar boards. A 42-inch top rail on the other three sides is within the 38–45 inch range, but the open face means the only barrier between a worker and a 28-ft drop is nothing.
Medium-high - footing. Two legs on 4-inch concrete block is unstable; block crushes and shifts. Base plates on adjustable screw jacks bearing on mudsills sized for the load is the requirement.
Medium - access. Cross braces are expressly prohibited as a means of access. A ladder, stair tower, or hook-on ladder is required, and the cross braces are structural, so climbing them also damages them.
Medium - the 18-inch setback. Normal maximum gap between platform and work face is 14 inches. The planking is fully planked, but the brick ledge is now a hazard in its own right.
2. At 28 ft, what fall protection is required, and where exactly does the 18-inch setback become a problem?
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Threshold: employees on a scaffold more than 10 ft above a lower level must be protected by a guardrail system or a personal fall arrest system; guardrails are the default on a scaffold. So this crew needs guardrails on all open sides and ends - the street side is missing one entirely.
Required components: top rail 38–45 inches (42 is compliant), a midrail approximately halfway, and toeboards where materials could fall to people below. The rail must withstand the required load without failure.
Where the 18 inches bites: two ways.
- The standard limits the gap between the platform and the face of the work to about 14 inches precisely so a worker cannot step or fall through the gap. At 18 inches, a foot, a knee, or a whole body can go through that slot. Either plank out to within 14 inches of the wall or install guardrail or a fall arrest system on that side.
- The ledge that the setback was meant to clear is itself a trip and fall edge at 28 ft, and a fall from that height onto a mortar board or a brick stack at grade is not survivable.
Also note the wind rule: work on scaffolds during storms or high winds is prohibited unless a competent person determines it is safe and employees are protected against the wind. Guardrails are not wind protection, and the missing ties mean the structure cannot resist the gust load at all.
3. Before work resumes, what must be corrected, and who is authorized to make these calls?
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Sequence matters. Nothing goes back on that scaffold until the structural question is settled; fixing guardrails on a tower that may tip is arranging furniture in a building that is falling down.
- **Stop work and clear the scaffold and the area beneath it.
- Ties: a competent person determines the tie pattern and spacing for a 28-ft tower, and the scaffold is tied or guyed on all faces accordingly, or the height is reduced.
- Footing: base plates on adjustable bases on mudsills sized for the load, on firm, drained, level ground. Concrete block comes out.
- Guardrails and toeboards on all open sides and ends, including the street side; close the platform-to-wall gap to 14 inches or less.
- Access: a proper ladder or stair tower, secured, extending above the platform, with cross braces left to do their job.
- Re-inspection: a competent person inspects before each shift and after any event - including this wind event - that could affect the scaffold.
Who decides: the competent person for scaffolds, designated by the employer, makes the structural and inspection calls. The site superintendent or GC controls access and can shut the area down, but no one who is not a competent person should be the one signing off that a wind-loaded, untied scaffold is safe to occupy. If the tie design is outside the manufacturer's tables, it is an engineer's call.