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Plank or Platform?

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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?

Platform or Plank?

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Is this a tough question?  Is plank a platform or is the platform a plank?  Here is a primer on what constitutes a safe scaffold platform.  Of course, that begs the question as to whether you can have an unsafe platform.  And the answer to that question is pretty easy: yes.  If that is the case, then why are you using an unsafe platform?  Do you know if you are using an unsafe platform?  Now there is a question that is worth answering.  What basis should we use to determine is a platform is safe?  Should we wing it and see what happens?  Should I make up stuff that sounds good so it looks like I’m the guy that knows everything?  Perhaps not.  How about if we use “typical industry practice” and the safety standards as a basis for establishing the criteria for a safe platform?

A scaffold platform can be constructed of many materials although the most common materials include wood plank and manufactured plank.  Wood plank is solid sawn from a tree while manufactured plank can use wood, aluminum, steel or plastic in its composition.  Furthermore, both solid sawn and manufactured planks are usually rectangular and the ends of manufactured plank may be square cut or have hooks on them to hook over the scaffold bearer.  In any event, the planks are purpose built for use with scaffolds.

There are two issues that must be addressed with plank.  The first is the strength of the plank and the second is the installation of the plank.  The strength of the plank is based on the material that is used.  If the plank is solid sawn, that is cut directly from a tree, its’ strength is directly related to the type of tree that it comes from.  In North America the two most common trees that are used for scaffold plank are Southern Yellow Pine and Douglas Fir Larch.  Although less common, Spruce is also used in certain locales.  (This doesn’t mean that you cannot use other trees, such as Balsa Wood, for a scaffold plank.  It’s just that your plank would be really big!  This is due to the fact that the dimensions of the plank are directly related to the strength.  Another way of saying this is the bigger the plank, the more it will support.  Or still another way of looking at it is to say that the weaker the tree, the bigger the plank must be.)  The common size for a scaffold plank is a nominal 2 inches by 10 inches which means that it is actually 1-1/2 inches by 9-1/4 inches.  By specifying that you must use Southern Yellow Pine or Douglas Fir Larch, I then can tell you how much load you can put on that plank, based on a given span.  For example, if you use a Scaffold Grade Southern Yellow Pine plank and span 10 feet, you can safely put 250 pounds on the plank.  If you choose to use Balsa Wood, Willow, or Aspen, all bets are off; it’s time to get a qualified person to tell you what your plank can support.

If you choose to use manufactured plank, the solution is pretty easy:  contact the manufacturer for loading information.  These manufactured plank can be laminated veneer lumber, proprietary plank that use solid sawn wood, aluminum with plywood, all aluminum, steel, or plastic.  While the laminated veneer lumber plank may look like solid sawn plank, the loading characteristics will vary so check with the manufacturer.

The second issue that involves the use of plank is the installation.  The name of the game is to make sure that when you stand on a platform you will remain at that elevation.  It is never good to step on a platform and find out you are quickly descending to a lower unanticipated location.  The end result usually is detrimental to your health.  So, what needs to be done to ensure you stay where you are?  Well that’s easy; make sure the platform is installed correctly.  What does that mean, you ask?  The easy answer is to make sure that whatever you use to construct your platform it will stay where you place it.  With 2×10 plank that means that the plank overhangs its support at least 6 inches but not too much so you create a diving board.  Usually that means a maximum overhang of 12 inches for plank 10 feet and less in length and 18 inches for longer plank.  Of course, if you secure the plank the overhang can be less than the 6 inches and more than the 12 or 18 inches.  For planks that have hooks, the solution is straightforward; use the right length plank for the space.  Other requirements for platforms include:  make sure the space between plank is 1 inch of less; make sure the maximum space between the back edge of the platform and the guardrail is no more than 9-1/2 inches; make sure the platform is close enough to the work surface (depending on the jurisdiction, this distance varies from 3 inches to 18 inches); make sure the platform is not slippery; make sure debris isn’t allowed to pile up on the platform; make sure the platform isn’t overloaded and finally, make sure the scaffold user is properly trained.  Why is this important?  We want to make sure the user understands the platform capacity so it doesn’t get overloaded.  Let’s face it, the only good platform is a safe platform.

How Much More?

By | OSHA Standards & Regulations, Resources, Scaffolding | No Comments

A description of the strength and safety of suspended scaffolds

How much more can we do? Will more standards increase the safety of suspended scaffolds? Will training increase the safety of suspended scaffolds? Will more safety features increase the safety of suspended scaffolds? Wait—is there a problem that needs to be addressed or are suspended scaffolds safe? It is always interesting when I first meet someone and tell them I am involved with scaffolding. Sooner rather than later they tell me how dangerous it all must be and how could I still be alive? And when I tell them that a properly constructed scaffold, including one hanging down the side of a building by ropes is completely safe, they just insist that I must not know what I am talking about.

If you look at the statistics, they are correct; unfortunately they missed the word “properly” when I say that a properly constructed suspended scaffold is safe. The injury and fatality statistics do indicate that there are issues with scaffolds, particularly suspended scaffolds, those scaffolds that have “one or more platforms suspended by ropes or other non-rigid means from an overhead structure.” A commonly seen example is the scaffold platform that is used by workers to perform maintenance to the face of a high rise building. And of course, it is also commonly seen on the evening television news when there is a scaffold failure—it makes great footage for the local and national news crews.

I thought it would be an educational exercise to see how many US federal OSHA scaffold standards specifically address and/or require safety items for a typical single or two point suspended scaffold. There are four primary components of a suspended scaffold, the rigging, the platform, the hoist, and the personnel safety protection. Each of these components has requirements that go beyond the basic function of that component. For example, the rope that the platform hangs from is much stronger than what is required to support the load. This is called the safety factor; its purpose is to make sure that the scaffold doesn’t collapse because an errant worker damaged the suspension rope while using the scaffold. So, here is the list I came up with—can you add to it?

Rigging: 6 to 1 safety factor on the rope (wow that is high!); 4 to 1 safety factor on the beams and counterweights (that’s high too!); Design by a qualified person; Installation under the supervision of a competent person; A tieback rope to hold the rigging in position and not let it slide off the roof; non-flowable counterweight; For multi-point suspended scaffolds, the design to be completed by a qualified Professional Engineer; When it is secured directly to the structure it shall be evaluated by a competent person; Counterweights shall be secured to the outrigger beam; Ropes shall be inspected before each workhshift (Actually the whole scaffold shall be inspected before each workshift); 3 wire rope clips shall be used (instead of the normal 2 required for rigging materials);

Platform: The normal width shall not exceed 36 inches; The fasteners securing the platform to the hoist shall have a 4 to 1 safety factor; The platform shall have a 4 to 1 safety factor; The platform shall not swing (In spite of the fact that we sometimes call them “swing scaffolds”); A guardrail system shall be installed on all open sides of the platform.

Hoist: The rope shall be long enough or have a stop so the end of the rope doesn’t pass through the hoist; The hoist shall be tested by a qualified testing laboratory; The hoist shall have an operating over-speed brake; The hoist shall have a 4 to 1 safety factor.

Personnel Protection: All occupants shall wear and utilize proper personal fall protection. The anchor for the vertical lifeline shall be independent of the scaffold rigging; The lifeline anchor shall hold 5,000 pounds or be designed by a qualified person to have a 2 to 1 safety factor; The employer shall provide for prompt rescue of employees in the event of a fall or shall assure that employees are able to rescue themselves; The user has to have training in the proper use of the scaffold, including all the safety items.

That’s quite a list. Let’s sum it up: The rigging, hoist and platform have to be really strong. The suspension rope has to be really, really strong. Not only does the platform have to have a guardrail system so the worker doesn’t walk off the platform, but the worker has to utilize personal fall protection so she doesn’t fall in case the platform disappears. In the event of that occurrence, the worker who is hanging around must be promptly rescued. (Yeah, like that always happens—that’s what makes the evening news so interesting. Nobody planned to get the guy down that’s hanging on the side of the building.)

So how can it be that suspended scaffolds fail? Everything has more strength than is required, the workers are trained, the equipment is constantly inspected for defects, and a rescue plan is in place. Perhaps the evening news should be more thorough in its investigation. You figure it out—do we need more rules or do we just have to use the ones we have?