Platform requirements can be put into two groups, construction and strength. That’s it. There are no secrets here. Perhaps the confusion originates with the fact that all the standards, U.S., Canadian, and state, zero in on the use of wood planks, such as 2×10 solid wood planks (in spite of the fact that the U.S. federal OSHA standards only acknowledge individual planks as “platform units”) and ignore all the other possibilities that exist for the construction of scaffold platforms. To state things simply, all that is expected of erectors and users is to build the platform correctly and make sure the platform is strong enough. Unfortunately, that’s straightforward only until someone asks what is “correct.” So let’s take a look at what makes a platform correct and see if we can make sense of the confusion. We’ll look at the easy one first: strength.
All platforms must be strong enough to not only support the intended load but also have a safety factor of 4. This means that the platform must be 4 times stronger than the load that you are going to put on it. If you plan on placing 1,000 pounds on the platform, then the platform must hold 4,000 pounds before it breaks. That’s it! I doubt it can get much easier than that. Of course, you have to know how strong the platform is. How do you do that? You can either calculate the capacity, if you know how to do that, or you can use a platform that was designed by a qualified person and the strength has been determined. For example, if you use a wood plank of known type and grade, a qualified person can tell you how much load you can put on it for a given span. Other products, such as an aluminum hook plank, will have the capacity indicated somewhere on that plank. It is up to you, if you are the user, to know that strength, and not put more load on the plank than what is intended. I think this is straightforward; do you? Let’s say you have four 2×10 wood plank spanning 7 feet on a scaffold and a qualified person told you that you could safely put 400 pounds on each plank. This would mean that you could put 1,600 pounds (4 plank x 400 pounds for each plank = 1,600 pounds) on the platform, provided that the load was spread out over all 4 plank. What this means is that you get to make sure you comply with the regulations and not overload the plank.
As for the construction of platforms, the bottom line is that you want the platform to stay where it is. We also like to keep you on the platform by making sure you have fall protection such as guardrails but of course, what good are the guardrails if your platform disappears. Most codes specify minimum expectations for the installation of plank. Generally speaking the planks have to hang over their supports at least 6 inches and not more than 12 or 18 inches depending on the length of the plank. If you overlap plank, make it at least 12 inches. If you choose to secure your plank from movement, by whatever method you choose as long as it works, then don’t worry about the overhang and overlap requirements; they don’t apply anymore since you have eliminated the hazard by securing the plank. We don’t like to have gaps between the planks so keep it to 1 inch please. We also want to make sure you have enough room on the platform so don’t make it any smaller than 18 inches wide unless of course, you don’t have any room to make it 18 inches wide. Then make it as wide as you can and use fall protection.
What about other platform materials? What happens if you use 4×4 wood members with plywood on top? Well, as long as the platform has been designed by a qualified person, it’s okay, as long as you know how strong it is so you don’t overload it. Make sure your design addresses bearing and movement. Remember, we don’t want the platform to disappear on you. One issue that comes up is the use of plywood with 2×10 scaffold plank. As far as I’m concerned this is no different than using 4×4’s. As long as it is designed by a qualified person, it’s okay. U.S. Federal OSHA came out with a Letter of Interpretation suggesting you couldn’t do it because you couldn’t inspect the plank. That’s nonsense. If the platform is constructed and used properly, there is no justifiable reason to tear up the plywood before each work shift, especially since you can check plank bearing from below.
Just remember that you need to know how much load you can put on a platform before you use it. And you need to make sure that platform stays where it is intended to be. Finally, just because the plank you use is a 2×10 doesn’t mean that it’s a scaffold grade plank. If you confirm that your platform is strong enough and it won’t go anywhere while you are on it, then your descent from the scaffold platform will not be a premature surprise!