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January 2007

Is it Real Protection?

By | OSHA Standards & Regulations, Resources, Safety Hazards | No Comments

Do you think you are really protected from falling objects when passing by a construction site?  Sure, you stand under a scaffold platform that’s fully decked and assume nothing will harm you.  But how do you know that platform is strong enough to protect you from falling objects?

Falling object protection requirements are addressed in a variety of standards, including the Federal Occupational Safety and Health Administration (OSHA) standards, American National Standards Institute (ANSI) standards, and the International Building Code (IBC) standards.  OSHA’s standards address falling object protection for scaffold users in Subpart L of the Construction Standards and for other workers passing under a scaffold in Subpart M of the Construction Industry Standards.  ANSI addresses falling object protection for scaffolds in ANSI A10.8-2001 and the IBC concerns itself with pedestrian safety during construction.

There are several options that can be used to protect people from the hazard of falling objects.  One of the more common options is the use of toeboards and this can be an effective choice for scaffold platforms in many instances.  Canopies can be used to provide protection for employees working on scaffolds and they can also be used to protect employees passing under the scaffold.  Canopies are especially effective for protecting the perimeter of a jobsite, if they are designed and constructed properly.  In fact, most urban jobsites are required to provide a canopy/covered walkway since sidewalk access is normally expected, even during construction.

To safeguard pedestrians, the IBC specifies the strength and dimensional parameters for sidewalk canopies.  While many cities adopt these standards, others have there own specific requirements.  If you are the provider of a sidewalk canopy, you are expected to know what these requirements are.  Basically, covered walkways must withstand the force of a falling object.  The IBC requires that all walkways “shall be designed to support all imposed loads and in no case shall the design live load be less than 150 pounds per square foot (psf).”  Installing a tubular welded frame scaffold with a few wood plank on top and plywood will not suffice for these loads.  Besides, the force of falling debris can easily exceed the 150 psf load requirement and will most certainly exceed the capacity of plywood and wood plank.  For example, if an errant worker were to drop a 20 pound object from 3 stories above the canopy, the force could easily be above 1000 pounds.  In fact, from ten stories the results would not be well for anybody under this type of canopy!

Besides the strength requirement, the IBC specifies the minimum clear width and height of a covered walkway.   The minimum allowable width is 4 feet and the minimum height is 8 feet.  Of course, both of these dimensions may need to be greater to accommodate the expected pedestrian traffic.  (Again, some cities will have stricter regulations.)  Lighting, splash shields, and barriers may also be required to protect pedestrians from construction activity and adjacent traffic.  In certain instances concrete traffic barriers may also be required.  Wind loads must also be considered, particularly if the walkway is enclosed.  Based on these requirements, how well do scaffold frames perform under these circumstances?  The quick answer is: It all depends.

On average, a one tier tall scaffold frame can support about 3000 pounds per leg.  Since the ledger capacity is dependent on the width of the frame, that capacity will vary, decreasing as the frame width increases.  Let’s say that you decide to install a covered walkway utilizing 5 foot wide frames and 10 foot crossbraces.  The IBC requires that each bay of the scaffold must support at least 7500 pounds.  Since you want to be competitive, you cleverly use three wood plank and an old piece of plywood for the cover.  You nail it down so it doesn’t go anywhere and decide it looks pretty good.  That platform may safely hold 1800 pounds, if you play with the safety factor.  The last time I checked, 1800 pounds is less than 7500 pounds by a substantial margin.  Well, let’s just fully plank the thing and go have coffee.  Now you are up to maybe 3100 pounds, still a bit less than the required 7500 pounds!  It looks to me that maybe plank and plywood might not be the best choice for a proper cover.   Also remember that dropping a concrete block from ten stories will also have an impact, literally, on the cover.  Even if the cover can hold the load, don’t forget the ledger of the frame; it probably isn’t strong enough either.

What’s the solution?  The simplest solution is to keep people out from under the work above.  Since that isn’t always the practical or even permissible answer, a properly designed cover is required.  The qualified designer must ensure that it will work.  This means that it has to be designed to stop whatever missile will hit it.  One solution is to construct a catch platform directly under the falling object so that it doesn’t fall all the way down to the covered walkway, gaining speed and force as it drops.  As in fall protection, not even letting an object begin to fall is the best solution.  Since there are many variables, there are many solutions.  A covered walkway/canopy that looks good may not be any good.  Chances are, scaffold frames with plank and plywood won’t meet the minimum strength or dimensional requirements.  Keep that in mind the next time you walk through a covered walkway at a construction site.

Plank or Platform?

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

Is it plank or a platform that you stand on?  Is this a tough question?  Why is a concept so easy in theory so difficult in application?  The simple answer to the first question is that scaffold plank can be used to construct a platform.  For a variety of reasons, it gets complicated, or so it seems.

The Federal Occupational Safety and Health Administration, OSHA, describes a scaffold platform as a “work surface elevated above lower levels.  Platforms can be constructed using individual wood planks, fabricated planks, fabricated decks, and fabricated platforms.”  In an attempt to include the largest variety of products that can be used to construct a platform, OSHA refers to the various components as “platform units.”  While the experienced scaffolder will recognize that wood plank can be platform units, those not so knowledgeable will easily become confused since “platform unit” is not defined in the OSHA standards other than to say:  “Each platform unit (e.g. scaffold plank, fabricated plank, fabricated deck, or fabricated platform)” as a way of defining a platform unit.  The intent of the platform standards is to ensure a safe work surface for the scaffold user.  This means that the worker should expect a surface that has sufficient strength, doesn’t deflect too much, doesn’t have any big holes to fall through, and is relatively flat.

Having stated these expectations, where does that leave us when it comes to the specifics?  It depends on what you are using for “platform units.”  It also depends on the applicable scaffold standards.  Is it General Industry or Construction?  Let’s take a look at some of the things it takes to have a decent scaffold platform:

  • All platform units shall have a safety factor of four.  This means that if you are going to put 250 pounds on the platform unit, it has to hold at least 1,000 pounds before it breaks.
  • If you have a 2×10 plank, it has to be 4 times stronger than the load it will hold.
  • If you are using a platform unit as described above, in other words a 2×10 wood plank, a fabricated plank such as a laminated veneer lumber 2×10, or a fabricated deck (read that to be a hook plank) the space between units cannot be more than 1 inch.
  • If you are using solid sawn lumber for a platform unit, that is a plank cut out of a tree, it must be scaffold grade if OSHA General Industry standards apply, and it must have a 4 to 1 safety factor if OSHA Construction Industry standards apply.  (In Construction Industry applications, it does not have to be scaffold grade but the Scaffold Industry Association recommends that only scaffold grade solid sawn plank be used.)
  • You can use Styrofoam as a platform unit but you better make sure you have that 4 to 1 safety factor!
  • If you are using laminated veneer lumber, or other platform units fabricated from wood, again it has to have that 4 to 1 safety factor.
  • The minimum width of a scaffold platform, for most supported scaffolds, is 18 inches.  You can get by with less if you can show that you don’t have room to construct an 18 inch platform.
  • Platforms are to be “fully decked” between the front uprights and the guardrail system.  Great idea where a guardrail is being used.  I have no idea what that means when there is no guardrail.  Some people think that means the full width of the scaffold.  Suppose you have a nine foot wide (not long but wide) bay; does this mean the platform should be nine feet wide?
  • Platforms constructed with plank and plywood are legal, and safe too, notwithstanding an incorrect OSHA Letter of Interpretation that claimed one couldn’t inspect the plank if it was covered by plywood.
  • OSHA has a plank span chart in non-mandatory Appendix A of the Construction Scaffold standards.  You can follow this chart if you want.  Just make sure the plank you are using equals the strength used for the chart.  Of course, if your plank is stronger than what the chart is based on, then you can’t use the chart.  Get a qualified person to tell you what your plank can do.
  • Make sure you know what you are buying when it comes to plank.  Unscrupulous purveyors of scaffold plank have a tendency to overstate their products capability.  (If the deal sounds too good to be true, it probably is.)
  • If you choose to construct your platform with joists, such as aluminum beams, and plywood, make sure it is designed to support the intended load.  In other words, have a qualified person design it.
  • It is assumed that if platform units hang over their supports at least 6 inches they won’t fall off.  If you think your platform units may fall off, secure them so they don’t.
  • Don’t let your platform units hang over their supports too far as this will result in a diving board (also called a widow maker).  This is not good.  Unless you secure the opposite end, don’t let your platform units stick out more than 12 inches for platform units 10 feet or less in length or 18 inches for longer plank.
  • Overlap your platform units at least 12 inches unless you secure them.

Well, these are a few things to think about when you are installing or working on platform units.  Consult the OSHA, ANSI and SIA standards and codes for additional important information.  Remember this:  there is no back-up for a failed platform unit like there is for other scaffold components.  In engineering jargon, the platform has no redundancy.  If the platform unit you are standing on breaks you are history.  Some people suggest that the platform below will stop you.  Unfortunately, by the time you hit the deck below you will have built up enough energy to break that one too.  By the time you hit the ground you will have broken a lot of plank that you will have to pay for as soon as you get out of the hospital!  Don’t take chances on damaged product, misrepresented product, faulty product, or poorly placed product.  That’s what the standards say, in spite of the use of the term “platform unit.”