By David H. Glabe, P.E. / May 31, 1999

A friend with the Occupational Safety and Health Administration (OSHA) sent this sketch to me. He asked for my opinion concerning the safety of the installation and whether this scaffold complied with the OSHA Standards. What would you answer?


We can analyze this scaffold two ways:


1. Is this scaffold safe?

2. Is this scaffold in compliance with applicable standards?


Let’s look at the safety issue first. The platform is at two levels. Assuming that the frame is 5 feet tall and 5 feet wide, both platforms are less than five feet above the level below. Is this safe? If the platform is cantilevered over a boiling vat of sulfuric acid, you may want to consider fall protection. On the other hand, if the scaffold is in the local pillow factory, there probably isn’t any problem. What about the width of the platform? What about the relative relationship between the two platforms? What about having the lower platform supported by an intermediate horizontal support, typically a member that is about 1 inch in diameter? Is there safe access? What work activity is this scaffold supporting? These are questions that the competent person should ask when evaluating this scaffold.


Typically the scaffold industry accepts the fact that a work platform should be at least 18 inches wide, meaning that two 2×10 planks is the minimum platform width. (This fact is confirmed by OSHA, ANSI, and Cal/Osha.) It would appear that this scaffold meets those criteria. However, it seems that a hazard could exist due to the gap between the platforms, especially since these platforms are at approximately the same elevation. A worker, concentrating on his/her work, may quickly look over, see a platform, and think it is continuous; stepping backward would be disastrous!


An intermediate ledger supports the lower platform. Is this permissible? Sure it is, limited only by the strength of the supporting member. Under normal circumstances, this smaller diameter ledger will still be stronger than the typical platform. In fact, the beauty of these frames is that they can support platforms at different elevations, and they can support the side brackets at various elevations too.


Access via the frame is probably not possible due to the overhang of the plank. A clamp-on ladder or other safe means of access would be required. Finally, there is a danger of the scaffold over-turning due to an excessive load on the side bracket platform. The scaffold would require counterweights or a tie to another substantial structure to be sure that the scaffold would remain stable.


Analyzing the scaffold based on the applicable Federal OSHA Standards will produce similar results as the first analysis. This shouldn’t be surprising since the standards have been established to address hazards such as the ones already described. The most common question that is asked regarding a scaffold such as this one concerns the width of the platform. Regulation 29CFR 1926.451(b)(1) frankly states that “each platform on all working levels of scaffolds shall be fully planked or decked between the front uprights and the guardrail supports as follows…” If you think that this means that the platform should be across the full width of the frame, take another look at the side bracket platform. Where is the upright? Where is the guardrail support? The upright is behind the platform, and there is no guardrail support! What’s a worker to do? For that matter, what’s a compliance officer to do? Ask the questions: What is the intent of this regulation? What hazard does this regulation address? It’s simple, the regulation addresses fall protection. Since this platform is only 5 feet above the level below, there is no hazard, based on the OSHA fall protection standards. The standard, in particular 29CFR 1926.451(b)(2), requires that all frame scaffold platforms shall be a minimum 18 inches wide except in certain specific circumstances. The platforms on this scaffold comply with this regulation.


Do any standards address the intermediate ledger that supports the lower platform? The answer is found in 29CFR1926.451(a)(1) which specifies that “each scaffold and scaffold component must be capable of supporting, without failure, its own weight and at least 4 times the maximum intended load applied or transmitted to it.” As long as the live load applied to the ledger is no more than 25 per cent of the maximum load it can support, we are in compliance with the regulations.


As described earlier, access via the frame rungs/ledgers, is not permitted due to the assumed overhang of the plank. (If there is no overhang, and if the rungs/ledgers are spaced properly, the frame could be used as access.) As described in the standards, safe access includes stairs, clamp-on ladders, portable ladders, and direct access. Access between platforms would not be necessary if the horizontal distance between the platforms is less than 14 inches, and the vertical distance between platforms is no more than 24 inches. (See 29CFR1926.451(e)(8))


Finally, stability for this scaffold is addressed in the supported scaffold criteria sub-paragraph. Several regulations require that supported scaffolds, including frame scaffolds, shall always remain plumb and level.


In summary, this analysis shows that good construction practice can, in many instances, exceed the standards. This isn’t surprising since the standards are minimum requirements for the construction and use of scaffolds. The analysis also shows that:


1. The minimum width of a typical frame scaffold platform is 18 inches.

2. Workers on platforms more than 10 feet above the level below must have fall protection.

3. Platform fall protection may be required at lower heights, depending on exposure to hazards.

4. The platform does NOT have to extend all the way across the full width of the frame although this may be the easiest way to provide fall protection.

5. Access shall be provided for all platforms more than 24 inches above the level below.

6. Supported scaffolds must remain stable and plumb at all times.

Tags: Scaffolding Scaffolding Planks OSHA Standards & Regulations Resources Safety Hazards scaffold safety scaffold stability

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