Plank or Platform?

By David H. Glabe, P.E. / July 31, 2011

Is it a plank or is it a platform?  Can a plank be a platform or can a platform be a plank?  When it comes to the working surface for a scaffold, these questions are common.  But they shouldn’t be.  It appears the confusion arises because the use of wood planks for scaffold platforms is commonplace.  Simply stated, wood planks can be used as a platform.  Therefore, wood planks can be a platform but a platform is much more than just wood planks.  To understand this, it is good to know that typical scaffold standards address two issues with scaffold platforms.  The first is the strength of the platform and the second is the construction of the platform.

A scaffold platform can be constructed from any material provided that the material has sufficient strength to support four times the load that will be put on it.  This ratio of four is the safety factor.  For example, if you want to put 1,000 pounds on your scaffold platform, your platform has to support 4,000 pounds.  That’s pretty simple assuming you know how strong the platform is and you also know the weight of the workers and materials you will be placing on the platform.  If you don’t know these two things, then you cannot determine if the platform is overloaded and consequently you will be in violation of the standard that requires a 4 to 1 safety factor.  I cannot help you with the load you are placing on the platform; it is impolite to ask people how much they weigh.  However, depending on what material you are using for the platform, I may be able to help with how much the platform can support.

If you choose Styrofoam for your platform you are out of luck—I don’t know the strength of Styrofoam.  If you choose a fabricated plank, like an aluminum hook plank or a laminated veneer lumber (lvl) plank, the manufacturer can tell you how strong their product is.  Of course, if you don’t know who the manufacturer is or the manufacturer hasn’t tested their product to determine the strength, you are once again, out of luck.  However, if you decide to use a solid sawn Southern Yellow Pine scaffold grade plank, for example, you are in luck!  I can provide you with a chart that shows the capacity.  Keep in mind that the U.S. federal OSHA standards do not require the use of Scaffold Grade plank but if you do not know how to calculate the strength of the plank you are using, you will have a very difficult time convincing anyone that you have a sufficient safety factor.  That’s why it is prudent to use a scaffold grade plank when using solid sawn lumber for your scaffold platform.

The second issue, the construction of the platform, is cleverly addressed in some standards by referring to the components of the platform as “platform units.”  While this is technically correct, it is reasonable to assume that the standard is talking about 2×10 wood planks.  Minimum standards require that scaffold users are provided with a platform that is safe, for example a platform which won’t become misplaced and dump the occupant to the level below.  The standards also want to eliminate hidden surprises such as cantilevered platforms that are inherently unstable, exposing the user to a potentially untimely demise.  The standards will normally specify the minimum overhang and maximum overhang for planks (platform units), the space between planks, and the distance not only from the work surface to the platform edge but also the maximum gap between the back edge of the platform and the guardrail system (assuming one is being utilized).  The bottom line to all this is to ensure that the scaffold has a safe, stable and complete platform.

The platform does not have to be 2×10 wood scaffold planks.  It actually can be Styrofoam.  It can be aluminum joists and plywood.  If you choose to use joists and plywood, how do the standards apply?  How do you take a standard that requires that “platform units” overhang their supports at least 6 inches and no more than 18 inches and apply it to a 4×4?  The answer is straightforward if one understands the intent of the platform standards:  If the platform is stable, it is safe.

While all this could be straightforward the reality is quite different.  There is no single set of standards.  Various governmental agencies have established their own specifications and they do not necessarily agree from one agency to the next.  For example, US federal OSHA specifies that the maximum overhang for a 12’-0” long “platform unit” is 18 inches, while the Army Corps of Engineers allows only 12 inches.  Go figure.  In California, the overhang can be as much as 18 inches, no matter what the length of the plank is.  Go figure.  Is there an explanation for these contradictory requirements?  I suppose there is but I am not aware of it.  I do know that varying requirements do not make it easy for scaffold erectors.

Is it a platform or is it a plank?  Or is it a platform unit?  12 or 18 inches?  What if it is 12 and a half inches when it should be 12?  Do you know the answer?

Tags: Scaffolding Platforms plank platform Resources scaffold scaffold platform

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