Scaffold design by regulation

The business of scaffolding is quite fascinating in that parts and pieces can be assembled in countless combinations to provide elevated worker access. Scaffolding can be built up from the ground, suspended from the top of buildings, and cantilevered off the sides of structures.

And, as an added plus, the parts and pieces can be assembled with minimal expertise and knowledge! For some workers, whether it conforms with applicable design parameters and regulations appears to be of little to no importance.

Interestingly, the parameters governing the design and construction of scaffolds has defaulted to the U.S. Occupational Safety & Health Administration, OSHA, regulations. It is accepted custom and practice that if a scaffold substantially conforms to the OSHA regulations, it is assumed safe and it is generally accepted that if you successfully assembled scaffold parts and pieces in a manner that won’t collapse, a safe and successful scaffold you have built. It’s a dangerous assumption since the one regulation that is consistently ignored is the one that requires a scaffold to be designed by a qualified person.

Pop quiz

OSHA defines a qualified person as “one who by possession of a recognized degree, certificate, or professional standing, or who by extensive knowledge, training, and experience, has successfully demonstrated his/her ability to solve or resolve problems related to the subject matter, the work, or the project.” Based on this definition, a qualified person will have scaffold knowledge that goes beyond just following the OSHA regulations and will have the ability to answer questions such as these presented here. Can you answer them correctly?

1. What is the difference between supported and suspended scaffolds?
2. What minimum safety factor is required for all supported scaffolds?
3. What information do you need to determine the safety factor?
4. How do you calculate the safety factor?
5. How do you determine if you, or anyone else, is a Qualified Person?
6. Are you a Qualified Person?
7. What’s the difference between a Qualified Person and a Competent Person?
8. What is typically the controlling component in a rolling tower (mobile scaffold)?
9. What’s the minimum number of 2x10 planks do you need to make a scaffold platform?
10. Do scaffold planks have to be scaffold grade?
11. Can you calculate the number of counterweights needed for a suspended scaffold cantilever beam (outrigger)?
12. If you choose to extend the suspended scaffold cantilever beam further than what is shown on a manufacturer’s charts, or you use an I-beam of your choosing, what information do you need to have to determine if it is safe?
13. Can you determine that the surface supporting “suspension scaffold support devices” is “capable of supporting at least 4 times the load imposed on them?”
14. What do you need to know to determine if a suspended scaffold tieback anchor is adequate?
15. What information do you need to calculate the strength of a toeboard?
16. What is the required strength of a scaffold toprail and what is the required minimum safety factor?
17. Is it true that the toprail must support any outward and downward force?
18. Can you calculate the actual load on a supported scaffold leg?
19. OSHA specifies the maximum horizontal and vertical tie spacings for supported scaffolds. Are there occasions when this is insufficient?
20. What do you need to know to calculate tie loads?
21. How many scaffold regulations are there?

Check your work

Here are the answers:

1. Supported scaffold platforms are supported by rigid means; suspended by non-rigid means. You need to know this in order to comply with the applicable regulations when designing a scaffold.
2. Four.
3. The allowable or ultimate load and the actual load.
4. Divide the ultimate load by the actual load.
5. You have to know the subject matter to determine if the person knows the subject matter. This can be a problem when, for example, an employer, or OSHA compliance officer is attempting to determine whether an individual is actually qualified.
6. Can you successfully demonstrate an ability to solve or resolve problems related to the subject matter, the work, or the project? If so, then you are a qualified person.
7. To put it in the vernacular, the competent person can recognize the hazard and has the authority to do something about it. The qualified person knows how to resolve the hazard. For example, the competent person notices the platform has excessive deflection, recognizing that it could be a hazard. She tells everyone to get off the platform. She then asks the qualified person to determine what the maximum permissible load can be placed on the platform, or, alternatively, asking the qualified person to design a stronger platform.
8. Casters.
9. Two, since the typical permissible minimum width platform is 18 inches. (458 mm)
10. No. But if you are a qualified person, you will be able to calculate the safety factor to ensure that it is at least four.
11. Well---can you? If not, you are not a qualified person in suspended scaffold design.
12. Material properties, Section Modulus, Moment of Inertia, Area, dimensional properties, anticipated loads, and the required safety factors.
13. Well---can you? Typically, this requirement is beyond the scope of the typical suspended scaffold qualified person. Therefore, it would be necessary to enlist the help of others, such as the structural engineer who designed the supporting surface, to give the scaffold qualified person the necessary information to verify that the surface will have at least a safety factor of four. Alternatively, if the suspended scaffold qualified person has the skills, education, and training to make the analysis, that, of course, is acceptable.
14. You must know the load on the anchor, the strength of the anchor, and the strength of the structure to which the anchor is attached.
15. The dimensional properties of the toeboard, the type of material, the Section Modulus, Moment of Inertia, and the Cross-sectional Area of the toeboard. Alternatively, if it is a manufactured item, just ask the manufacturer.
16. 200 pounds and there is no safety factor on the 200 pounds.
17. No. It “shall be capable of withstanding, without failure, a force applied in any downward or horizontal direction at any point along its top edge.” Note that it is not just outward, but any horizontal direction, that is in, out, and sideways.
18. Can you?
19. Absolutely. One example is when the scaffold is wrapped in enclosure material, such as netting.
20. Local wind conditions, shape of the scaffold and adjacent structure, height and location of the scaffold, knowledge of applicable codes, and the training and expertise to apply the American Society of Civil Engineers (ASCE) formulae, codes, and standards, to name a few.
21. A lot.

How did you do? Designing scaffolds is not the same as simply building a scaffold to comply with the OSHA regulations since the OSHA regulations are minimum requirements, not instructions or directions for design. A qualified person will incorporate the requirements specified in the regulations in the design, not use the regulations as the design.