It is true that a scaffold without a platform cannot be a scaffold since a scaffold is defined as a “temporary elevated platform and its supporting structure.” It can, therefore, be assumed that a platform is rather important. But it isn’t the OSHA standards, or any other regulations and guidelines that make a scaffold platform important; it is the absolutely critical nature of a platform that makes it imperative that scaffold designers, erectors, and yes, users fully understand what makes a scaffold platform safe for use. So, what makes a platform safe and how is its safety assured prior to placing the platform and its supporting structure to use? Let’s explore those issues through a series of frequently asked scaffold platform questions:
What materials can be used to construct a scaffold platform?
Anything can be used to construct a platform. Common materials included solid sawn wood members, manufactured wood products, aluminum, steel, fiberglass and plastic. In fact, even cardboard and concrete could be used although I doubt the erectors would appreciate installing concrete panels!
If solid sawn lumber is used to construct a platform, does it have to be “Scaffold Grade”?
It depends. Some standards, such as the U.S. Federal OSHA General Industry Standards, 29 CFR 1910, require the use of scaffold grade plank while the U.S. Federal OSHA Construction Industry Standards, 29 CFR 1926, do not. When designing for a construction industry application, if you are a qualified designer who can calculate lumber stresses and control the loads that will be applied to the lumber, then you can specify any wood you desire provided the lumber maintains a safety factor of at least 4 [29 CFR 1926.451(a)(1)]. Having said that, the Scaffold & Access Industry Association, SAIA, the Scaffold, Forming & Shoring Institute, SSFI, and industry professionals encourage the use of scaffold grade plank when using solid sawn lumber.
Do all planks have to extend (overhang) their supports by 6 inches minimum and 12 inches maximum?
No. If the plank is secured from movement so that the individual plank cannot slide off its support, it does not have to extend a minimum 6 inches over its support. Conversely, it can extend further than 12 inches (in some jurisdictions the maximum overhang is 18 inches) if the plank is secured from movement, including uplift. Of course the plank has to be designed so the use of a long overhang doesn’t result in an overstressed plank.
Which jurisdictions allow an 18 inch overhang?
If you are a scaffold designer, erector, inspector or user you should know the answer to this question. If you don’t know, get training for your jurisdiction. For example, federal OSHA allows overhangs up to 18 inches for plank longer than 10 feet, California allows 18 inches for any length plank and the US Army Corps of Engineers limits all plank overhang to 12 inches, regardless of plank length.
I have been told that nailing plank damages them. Can you nail plank together to keep them from moving?
Of course you can—its wood! If you pound in the nail in the same spot for a long time you’ll probably damage the plank but you really have to keep hammering it.
Is it true that you cannot install plywood on top of plank?
No. While at one time US federal OSHA issued a Letter of Interpretation (LOI) that claimed that you could not install plywood on top of plank, it was rescinded (the LOI went away). Keep in mind that once plywood is installed on top of plank, the plank become “joists” just as 2×4’s or 2×10’s (plank standing on edge) would be.
Speaking of joists, what can be used to support a plywood deck?
You can use whatever works. That doesn’t mean slapping down whatever is available—it means anything that works; any structural member that is designed by a qualified person (see US federal OSHA standard 29 CFR 1926.451(a)(6)) can be used. This includes solid sawn lumber, laminated veneer lumber, aluminum joists, steel beams, and tree trunks if you can figure out how strong they are.
Can I use balsa wood?
Sure, as long as it has the sufficient strength.
US federal OSHA specifies that a platform cannot deflect any more than 1/60 of the span when loaded. [29 CFR 1926.451(f)(16)] Does this apply to the typical manufactured plank that is made out of aluminum and has hooks on each end for hooking over its supports?
You it does. However, based on my experience, if your 10’-0” aluminum platform unit deflects 2 inches due to the load, you may have a serious overload problem.
A common practice is to install a “skip plank” platform where the plank are spaced at about 19 inches on center, resulting in a platform where every other plank is removed. This of course is covered with plywood and requires only half the plank to construct the platform. It has been claimed that a skip plank platform is as strong as a fully decked platform, especially because it seems to not deflect as much. Is this true?
How can it be as strong if it has half the plank? It just seems that way because the plywood helps to distribute the load to more than one plank, making it feel stronger. Don’t fool yourself—it is half as strong. Actually it is less than half as strong since the plank have to support the plywood.
You have mentioned plywood several times now. What thickness plywood is needed for a scaffold platform?
I cannot answer that. It all depends on the members supporting the plywood and the spacing of those members. Remember, and this is important, just because the plank supporting the plywood span 10 feet, doesn’t mean it is a “light duty scaffold.” Your platform must be designed by a qualified person, a person who knows how to calculate loads, use charts accurately and/or have the ability to “solve the problem.”
Can particleboard, oriented strand board (OSB) or flake board be used as a platform?
Sure. See the answer above about designing platforms.
Is there such a thing as an “OSHA approved plank”?
Nope. OSHA doesn’t approve any product. It is up to you to use the plank properly. If you don’t know how to do that, get some training.