Posts Tagged ‘scaffold’
October 4th, 2012 by David H. Glabe, P.E.
Tarps and other enclosure materials, such as plastic sheeting, are typical materials used to create a desirable work atmosphere. Many scaffolds are enclosed in screening and debris netting—I recall one resort project in Aruba where the scaffold was wrapped in a mesh to ensure, so I was told, that construction debris would not blow into the adjacent swimming pool. In reality it was there so the guests below couldn’t see the less than productive construction workers staring at them! And, of course, now that outdoor temperatures in North America are slowly falling, thoughts of a cozy work environment on a supported scaffold become more frequent, resulting in more scaffolds being wrapped in some type of enclosure so that work can continue. It is interesting that wrapped scaffolding has been frequently discussed and written about and yet each year scaffolds fall over because somebody wrapped the scaffold without giving much thought to the effects that the enclosure would have on the stability of the scaffold. Of course, one of the keys to a successfully constructed scaffold is making sure that the scaffold doesn’t fall over; this is especially important for the individuals who happen to be using the scaffold!
The concept of stability is straightforward: The forces that want to knock the scaffold over have to be resisted. How can this be done? While there may be a number of methods that can be used, there are three that are most commonly used by scaffolding designers and erectors:: tying the scaffold to another strong structure that can resist the forces; guying the scaffold tower to a suitable anchor that can resist the forces, and; making the scaffold large enough so the size and weight of the scaffold are adequate to keep the scaffold from falling over. Since the stability of a supported scaffold is desirable, standards and regulations have been written to address the issue. The U.S. Federal Occupational Safety & Health Administration, OSHA, requires that “Supported scaffolds with a height to base width ratio of more than four to one (4:1) shall be restrained from tipping by guying, tying, bracing, or equivalent means….” [29 CFR 1926.451(c)(1)] The standard goes on to require that when the scaffold is tied to an existing structure, it has to be tied at a frequency of no more than 30 feet horizontally and 26 feet vertically for scaffolds wider than 3 feet, and 20 feet vertically for scaffolds 3 feet and narrower. (In California the requirements are more restrictive.)
Unfortunately, this regulation can be very misleading for the simple reason that it doesn’t address varying field conditions. Keeping in mind that the OSHA scaffolding standards are minimum requirements and not directions or instructions, the qualified person who designs the scaffold shall determine the proper means and methods for ensuring the stability of a scaffold. Also keep in mind that a qualified person will not guess at what is required to ensure scaffold stability. Unfortunately, the reality is that too many scaffold erectors and users think that experience is a great method for determining what it will take to keep the scaffold from falling over. While the OSHA mandated requirements may work for a scaffold not wrapped in plastic, the same tying requirements will be woefully inadequate for a scaffold wrapped in a tarp and subjected to a violent winter storm. (Lucky for many wrappers, the enclosure material rips into pieces and blows off before the scaffold is yanked from its’ moorings!) When a scaffold is wrapped in a quality enclosure, that is a netting or enclosure that is resistant to tearing, the scaffold instead will rip, bend and ultimately fail.
Interestingly, #9 wire is often used to secure a scaffold to a structure. While this can work with an open scaffold design, it very rarely is adequate for a wrapped scaffold, even if the ties are “doubled up.” Remember, guessing never has worked well as a substitution for a properly designed and erected scaffold.
So, what is the worker to do? The answer is easy, logical, and in compliance with the applicable standards and good scaffolding engineering practice. Have a Qualified Person design the scaffold. In the case of a wrapped/enclosed scaffold, it will probably take the skills and expertise of a Qualified Professional Engineer who can design the scaffold for the anticipated forces at the specific scaffold location and for the specific time of year that the scaffold will be exposed to external forces from the wind and other environmental conditions.
If you think that you are qualified to design an enclosed scaffold answer yes or no to these statements. (If you answer no to any of them, you are not qualified to design an enclosed scaffold):
I know where to find the information that tells me what the design wind loads are for my scaffold location;
I am familiar with the American Society of Civil Engineers (ASCE) Standard, Minimum Design Loads for Buildings and Other Structures wind loading criteria;
I know the strength of #9 wire and why it shouldn’t be used for wrapped scaffolds;
I can calculate the forces that are a result of a 100 mph breeze;
I know how to calculate overturning moments and forces due to pressures;
I know what the effects of a partially wrapped scaffold are;
I know what happens if the windows are open;
I know what effects a building corner or roof has on a wrapped scaffold;
I know my limitations.
September 7th, 2012 by David H. Glabe, P.E.
Are you familiar with suspended scaffolds? Do you know the difference between a suspended scaffold and a hanging scaffold? Well, here’s a chance to show your friends and neighbors how well you know suspended scaffolds. Take this quiz and see if you are the best of the best.
The answers are at the bottom of the page—no cheating!
True or False
- ____A suspended scaffold is the same as a hanging scaffold.
- ____Outrigger scaffolds are one type of suspended scaffolds.
- ____You don’t need to utilize personal fall protection on a Multi-point Suspended Scaffold.
- ____Suspended scaffold users do not need any training if they are not operating the hoists on a suspended scaffold.
- ____Access is not required for a suspended scaffold.
- ____Counterweights for a cantilever beam can be ice or Jell-O.
- ____The safety factor for wire suspension ropes is at least 8.
- ____Counterweights cannot be used to stabilize outrigger beams on Mason Multi-point suspended scaffolds.
- ____Guardrails are not required on two point suspended scaffolds if all the occupants are wearing personal fall arrest equipment.
- ___Guardrails or equivalent are required on Boatswains’ chair scaffolds.
- ___Outrigger beams secured directly to the roof do not require tiebacks.
- ___Suspended scaffolds shall be designed by a competent person and installed under the supervision of a qualified person, competent in scaffold erection.
- ___Vertical pickup means a rope used to support the horizontal rope in catenary scaffolds.
- ___Tiebacks only need to be one half the strength of the suspension ropes since they are there for back-up, not suspension.
- ___Sand can be used as a counterweight provided it is in a sealed strong metal container.
Now for the tough part, fill in the blank!
- When wire rope clips are used on suspension scaffolds, there shall be a minimum of ________ installed per connection.
- A stage rated for two workers or 500 pounds can support ________workers.
- Ropes shall be inspected for defects by a competent person prior to each ___________.
- Manually operated hoists shall require a _________crank force to descend.
- Wire rope clips shall be installed according to the __________recommendations.
- A two-point suspended scaffold is supported by _________ suspension ropes.
- Two-point suspended scaffold platforms shall not be more than ______inches wide unless it is designed by a ________person to prevent _________conditions.
- Suspension scaffold means one or more platforms suspended by _____ or other _______means from an overhead structure.
- The toprail of a suspended scaffold guardrail system must be able to withstand a force of at least ________pounds.
True or False Answers:
- False. A hanging scaffold is constructed with rigid tubes while a suspended scaffold hangs from ropes.
- False. Outrigger Scaffolds are a type of supported scaffold.
- True. You need to install a guardrail system.
- False. All scaffold users need training.
- False. Proper access is required for all scaffolds.
- False. The ice may melt and you might eat the Jell-O.
- False. The minimum safety factor is 6.
- True. The beams must be anchored to the supporting structure.
- False. A guardrail system and PFE is required.
- False. How do you attach a guardrail to a chair?
- False. Suspended scaffolds shall be designed by a qualified person and installed under the supervision of a competent person, qualified in scaffold erection.
- False. Tiebacks must be equal in strength to the suspension rope.
- True. While not recommended, as long as the sand cannot leak out, it’s okay.
Fill in the Blank Answers:
- Depends on the weight of the workers. You can put 5 on if they only weigh 125 pounds each. Alternatively, if Bubba weighs 400 pounds, only he can be on it.
- 36, qualified, unstable
- Ropes, non-rigid
March 27th, 2012 by David H. Glabe, P.E.
Connections play a big part in the proper erection of a scaffold. Knowing how connections work, which products to use, and their strengths are important for both erectors and users.
Being well-connected may suggest that you have a strong bond with another person or at least you may have influence over another person’s behavior and action. Unfortunately, this article is not about that type of connection-you’ll have to go somewhere else for advice on being personally well-connected. But what about your scaffold; is your scaffold well connected? And what kind of connections are we talking about?
There are all kinds of connections found in scaffolding. In engineering terms, there are shear connections, tension connections, compression connections, moment connections, and bearing connections. These connections can be provided by bolts, nails, screws, wire, welds, glue, adhesives, tape, bubble gum, string, wire rope, friction devices, u-bolts, swaged fittings, fist-grips, expansion anchors, coupling pins, retainer pins, studs, rivets and bungee cords. Well bubble gum might be a reach but the rest are legitimate; the choice of connection depends on the required strength of the connection and the application. For example, using string to attach a frame scaffold to a building will only provide a tension tie (it works only for pulling, not pushing) and the string probably does not have the required strength. On the other hand, you could weld the same scaffold to the structure but then the weld would have to be cut when the scaffold is dismantled-probably not a good choice for this application.
Myths are pervasive in the scaffold business and often include connections. Can wire, specifically # 9, 10 or 12 gauge wire be used for connections? Do we need high strength bolts for everything scaffold related? Can I use duct tape? Are friction connections bad? And can I hang a supported scaffold by its coupling pin? The easy answers, in order, are: Maybe, maybe, doubtful, no, and perhaps.
Let’s start by looking at the issue surrounding the use of wire. Wire is often used to provide a connection between a supported scaffold and a structure to provide stability so the scaffold doesn’t fall over. While the federal Occupational Safety & Health Administration, OSHA, specifies that supported scaffolds be tied to a structure at certain intervals, it does not specify the strength. Therefore, anything can be used, including wire, string and duct tape, provided it is sufficiently strong. On the other hand, California OSHA, (CalOSHA), allows the use of #10 or double wrapped #12 wire to connect the scaffold to the structure. This is an interesting concept since it assumes that these size wires are adequately strong regardless of the circumstances; this is a bad approach since wrapping the scaffold with enclosure material will probably overload the wire connection. In another common application, scaffolders frequently want to secure a scaffold leg to a coupling pin using #9 wire in place of a retainer pin. This could be a bad idea since the wire may not be able to handle the shear (karate chop) load.
Clamps/couplers are commonly used with supported scaffolds, providing a rigid or swivel connection between two tubes. The clamps primarily rely on friction to provide the connection and there are those (whoever those are) that say this is bad—you should never rely on friction for the connection. They (whoever “they” are) apparently don’t realize that they (same folks) rely on friction to walk, drive, stop, sit, or eat. In spite of the “friction myth,” scaffold clamps work because trained scaffold erectors understand that the clamp has to be properly tightened to ensure a proper connection.
And what about the myth of high strength bolts? I have no idea where this myth started but for some reason everyone (whoever “everyone” is) thinks that only high strength bolts can be used for scaffold connections. Sure, if a high strength bolt is used as a connection on an aerial lift, for example, then you better replace it with the correct high strength bolt. But, come on, regular everyday bolts work for many applications. If you want to use high strength bolts everywhere that’s fine with me; just don’t tell me it’s required.
And what about that coupling pin/connector that aligns one scaffold leg on top of another? Since its primary purpose is to provide alignment what strength is required? Well, it doesn’t have to be very strong unless you decide you want to hang your scaffold (as opposed to suspending a scaffold from a rope). Now the coupling pin must have sufficient strength to hold up the entire scaffold that’s hanging. Usually the coupling pin isn’t strong enough. And guess what– the bolts have to be strong enough too. May I suggest having a qualified person design that connection before you kill someone? By the way, don’t necessarily rely on the manufacturer; he/she may have no idea what to tell you.
As for those funny little connectors that secure a suspended scaffold wire rope to an anchor, its best to make sure that they are installed correctly. These connectors, whether u-bolts, fist grips, or swaged fittings, they all rely on friction. In this case, definitely follow the manufacturer’s recommendations for torque specifications since this is the key to safe use. And, don’t forget that the correct size and quantity of u-bolts or fist grips are required.
That brings us to the use of duct tape. Applicable standards and good engineering practice dictate that all connections must have adequate strength to support 4 times the anticipated load. If you can tell me the strength of duct tape in tension, I’ll be happy to design a suspended scaffold for your use. Will it be a single point or two point suspended scaffold platform that you want? Oh wait, I forgot that you want to go up and down with suspended scaffold. I think the hoist is going to be a tricky one to design! Perhaps we should stick (no pun intended) to something a little more conventional.
March 25th, 2012 by David H. Glabe, P.E.
Identification of the correct safety factors for scaffold foundations.
Foundations are a necessary part of any scaffold, whether it is a supported scaffold, a suspended scaffold, or an aerial lift. Webster’s dictionary describes a foundation as “the natural or prepared ground or base on which some structure rests.” Webster goes on to describe a base as “a bottom support; that on which a thing stands or rests.” Without a foundation, or base, the scaffold is useless. Think about it: if a supported scaffold, that is a temporary elevated platform that is supported by rigid legs or posts, doesn’t have a solid foundation, it will collapse. The same is true for aerial lifts such as scissors lifts or boom lifts, where it is very important that the foundation is strong enough to support the machine.
What about suspended scaffolds, those elevated temporary platforms that are supported by non-rigid means such as ropes? Do they need foundations? You may want to answer no since the rigging that supports the rope is typically on the roof of the structure. But you would be wrong. While the word foundation is typically used to describe the lowest level of a building and is usually in the ground, for scaffolding it means much more than that. Think in terms of Webster’s definition for a base: “a bottom support; that on which a thing stands or rests.” In the case of suspended scaffolds, the “thing” is the rigging, such as a cantilever beam, while the “bottom support” is the roof of the building or other structure supporting the rigging. In other words, all scaffolds need foundations; it’s just that the foundation for suspended scaffold may be on the roof of the building.
This brings us to an interesting question about the strength of foundations: what safety factor is required for scaffold foundations? Should it be adequate as specified in the federal Occupational Safety & Health Administration (OSHA) Construction Industry supported scaffold standards or should it have a safety factor of four as specified in the capacity standards? But wait, there’s more! The OSHA Construction Industry suspended scaffold criteria specifies that “all suspension scaffold support devices, such as outrigger beams, cornice hooks, parapet clamps, and similar devices shall rest on surfaces capable of supporting at least 4 times the load imposed on them by the scaffold operating at the rated load of the hoist (or at least 1.5 times the load imposed on them by the scaffold at the stall capacity of the hoist, whichever is greater.)” [29 CFR 1926.451(d)(1)] For suspended scaffolds this means the supporting surface, such as the roof of a building, should have a safety factor of 4. For example, if you had a 1,000 pound load supported by a beam that cantilevered 18 inches past the edge of the roof, and the beam had a backspan of 10 feet, the fulcrum load would be 1,150 pounds while the required counterweight at the back of the beam for such a situation would have to be 600 pounds. In our example the roof would have to support 1,750 pounds of actual weight. This is like parking a couple of Harley Davidson Electra Glide Classics on the roof. Picture that in your mind! Frankly, my experience suggests that not too many suspended scaffold erectors give this loading thing much thought. But then, they probably don’t think about parking Harleys on the roof either. Applying a safety factor of 4, the roof would have to support 4,600 pounds at the fulcrum. That’s a lot of load. At the back end of the beam the roof would have to support 2,400 pounds meaning that the roof would have to support 4,000 pounds + 2,400 pounds for a total of 6,400 pounds. In other words, the roof would have to hold the equivalent of a Chevy Crew Cab pickup truck. Is this really necessary? How many roofs do you think can hold a load of this magnitude? Do the standards really require this?
While the snappy quick answer may be yes, the best way to answer this is to determine what the hazard is and what the intent of the standard is. The hazard, of course, is that the roof collapses under the load of the hoist. Therefore, the intent of the standard is to make sure you don’t collapse the roof while using a suspended scaffold; not a bad reason for having the regulation. The tricky part is how to determine if the roof will have a 4 to 1 safety factor against collapse. Related to that question is determining how much of the roof you can use to support the rigging. Since the fulcrum is often a point load, there is a real possibility of having the fulcrum poke a hole in the roof. That would not be good. Therefore, this load has to be spread out. The same may hold true for the back end, depending on how the counterweights are rigged.
Most outrigger applications are designed by “experience,” that is gut feel as to the strength of the roof. If the roof happens to be new concrete, your gut just might be right. On the other hand, if the roof is a hundred years old and decayed, your gut may not be right at all and you’ll get indigestion, not to mention what the roof might be doing.
The bottom line is that, just like the rigging, the supporting surface (the roof) must also have a safety factor of 4. In our previously mentioned example, the actual load that has to be supported is 1,750 pounds, two Harleys. Depending on the roof construction, for example the direction of the support beams and the design live load, you may be okay. For illustration, if the roof design live load is 20 pounds per square foot (psf), and the outrigger beams are spaced at least 20 feet apart, the roof just might work with the required safety factor. Of course, if the live load includes the design snow load, and it snows, your safety factor will melt away before the snow does!
In other words, if you have been guessing about the roof strength, you may have a correct safety factor —or not.
March 1st, 2012 by David H. Glabe, P.E.
A description of the proper use of a knee-out.
There are two issues that need to be addressed when considering the use of a knee-out in your scaffold. The first issue involves the stability of the scaffold while the second issue involves leg loading. Stability can be a real problem if the base width of the scaffold that the knee-out is attached to is narrow compared to the size of the knee-out. While “off the shelf” knee-outs normally do not exceed 45 inches in the horizontal dimension, a knee-out can be any size you want—if you know how to design and construct it. Let’s say you have a scaffold that has a base width dimension of 5 feet. You decide to install a knee-out on the outside leg of the scaffold that happens to be 7 feet, measured horizontally. If you don’t have enough weight in the base scaffold, the whole thing will fall over. Of course, the clever, or not so clever, scaffold erector assumes the weight of the scaffold will be the “counterweight” for the knee-out. Imagine what happens if the knee-out gets loaded up with plank and materials that weigh more than the scaffold equipment or, better yet, somebody decides to dismantle the base scaffold first before dismantling the knee-out. The dismantling may not take as long as you thought!
Knee-outs have a direct impact on the leg to which it is attached. Assuming that an upper scaffold leg is supported by the knee-out and built up from there, there are two types of forces that the supporting scaffold leg must support, vertical forces and horizontal forces. The vertical loads from the knee-out are transferred into the supporting leg and presumably down to the scaffold foundation. The connection to the leg at the top of the knee-out has to resist a horizontal force that wants to pull the leg outward while the bottom connection of the knee-out wants to push the leg inward.
Since supported scaffold legs, normally a steel tube for frame, systems, and tube & clamp supported scaffolds, can handle vertical/axial loads efficiently, the vertical force is no big deal as long as the total load of the knee-out vertical load and the supporting scaffold leg do not exceed the allowable load for the supporting leg. Remember, the supporting leg is basically holding up two legs, and the loads on those two legs.
The horizontal forces are a little trickier. Round tubes can handle vertical loads well but do a really lousy job of handling horizontal loads, exactly the horizontal forces/loads that a knee-out applies to a round tube. What is a designer to do? Well, the qualified designer knows that bracing is required to transfer the imposed loads properly so none of the scaffold components are overloaded. This load transfer can be achieved in a variety of ways. The first requirement is to install a horizontal member at the knee-out connection so that at least two legs are connected horizontally. Then a vertical diagonal is required to transfer the load down to the next runner location, typically one frame down if it is a frame scaffold, and 6’-6” or so if it is a systems scaffold or tube & clamp scaffold. This process is repeated until either the vertical legs can handle and disperse the horizontal loads to other legs, or you have transferred the loads through the bracing down to the foundation. How do you know when that occurs? Well, there are two ways; analyze the scaffold or try it out and see if it bends! I strongly recommend the analysis method rather than the guess method—workers’ lives are at stake here.
Another issue that comes up, and is usually not considered by erectors guessing and “winging it” involves the diagonal member that transfers the leg load supported by the knee-out to the supporting leg. If that member is installed at a 45 degree angle, the force/load in the member is almost 1.5 times (1.404 to be exact) more than the leg load it is supporting. And since this diagonal member is in compression, it also must be braced when the length exceeds its ability to support the expected load. This is the stuff of qualified designers, typically qualified engineers who can develop an appropriate design for the specific situation.
If you can’t ascertain the loads the knee-out is subjected to, if you cannot calculate the horizontal forces applied to the supporting scaffold, if you cannot figure out how to transfer the applied loads so the scaffold can handle them, don’t guess at it; leave it to the experts to design it for you.
February 1st, 2012 by David H. Glabe, P.E.
A quiz that evaluates your understanding of the correct installation and use of supported scaffold platforms and fall protection.
How well do you know the mandatory standards that dictate how we are to build scaffolds? Specifically, how well do you know the mandatory standards that counsel us in the proper design and construction of scaffold platforms and fall protection? Let’s find out!
Here is a quiz to see if you know your stuff. The answers can be found below. The first set of questions is “true or false” while the second set is “fill in the blank.” No cheating on this; try it first from memory and if you don’t get a perfect score see if you can find the correct answer in the federal OSHA standards. And don’t look at the answers until you are done!
- All scaffolds need at least one platform to be a scaffold.
- The minimum width platform for a suspended scaffold is 24 inches.
- The maximum width platform for a two point suspended scaffold is 48 inches.
- A boom lift does not need a guardrail system.
- You can guess at the required strength of a fall protection anchor as long as it looks like it can hold 5,000 pounds.
- Plank used for a platform can be of any material and strength as long as it can hold four times the intended load.
- Aluminum plank cannot be used with steel scaffolding because of galvanic action.
- The minimum distance a solid sawn wood plank must overhang its support is 12 inches unless it is secured from movement.
- The height of a toprail above a scaffold platform is 42 inches, plus or minus 3 inches.
- You must wear personal fall protection equipment and have a guardrail system when working on a multi-point suspended scaffold.
- If you are wearing personal fall protection while on a tubular welded frame scaffold platform, you don’t need a guardrail if the platform is no more than 7 feet above the level below.
- Same question, different platform height: If you are wearing personal fall protection while on a tubular welded frame scaffold, you don’t need a guardrail if the platform is no more than 12 feet above the level below.
- Toeboards are part of the guardrail system.
- If you know you are not going to fall, you don’t need fall protection while on a scaffold.
- You have to wear personal fall protection and have a guardrail on a mobile scaffold if you are going to ride it.
Answers to the True and False Questions: 1, True; 2, False; 3, False; 4, False; 5, False; 6, True; 7, False; 8, False; 9, False; 10, False; 11, Trick question—you don’t need fall protection because the platform is less than ten feet above the lower level — True; 12, True; 13, False; 14, Don’t you wish-False; 15, False, but then if you are riding it you like to tempt fate.
Fill inthe blank
- The maximum gap between platform units is ___________________ inches.
- The minimum toprail strength is ______________________ pounds.
- The height at which fall protection is required on scaffolds is _____________ feet.
- The minimum overlap for plank is _____________ inches unless the plank is secured from movement.
- The minimum width platform on a supported scaffold is _____________inches.
- Fall protection for scaffold erectors is determined by the _____________________ competent person.
- For a platform on a supported scaffold, the platform shall extend from the front _________________ to the _________________ supports.
- Designed personal fall protection anchors must have a safety factor of _____ to one.
- Scaffold Platforms shall be designed by a _________________ person.
- The maximum space between the edge of the platform to the guardrail system is _________________ inches.
- For normal use, if the front edge of the platform is no more than __________ inches from the work surface, it is not considered an open sided edge and does not need fall protection.
- The stamp on the side of a scaffold grade plank shall read: ________________________.
- If an 8’0’ long plank is not secured, the maximum cantilever past its support is _________inches.
- The maximum distance between guardrail posts on a scaffold is ___________ feet.
- When you hook off the lanyard of your personal fall protection system to the toprail of a scaffold guardrail system, the rail has to be able to support __________pounds.
Answers to Fill in the Blank questions: 16, one; 17, two hundred; 18, ten; 19, twelve; 20, eighteen; 21, employer’s; 22, uprights, guardrail; 23, two; 24, qualified; 25, nine and one half; 26, fourteen; 27, it shouldn’t read anything– there is no requirement; 28, twelve; 29, trick question—there is no maximum as long as the rails can support 200 pounds; 30, 200—your personal fall protection isn’t being used since you are behind the guardrail, you are just “storing” your hook!
January 15th, 2012 by David H. Glabe, P.E.
Masons are allowed to be exposed to fall hazards due to over-hand bricklaying while on steel supported scaffolds; the use of side brackets (knee-outs) with supported scaffolds.
It is difficult to imagine masonry construction without scaffolding. Prior to the advent of steel frame scaffolding, Bricklayer’s Square scaffolding was used to provide an elevated work platform for the masons to conduct their work. Starting in the 1930’s, steel scaffold frames slowly replaced the wood scaffolds commonly used by masons. Adjustable scaffolds, specifically designed for masons, became available in the 1970’s and the evolution continues today with mast climbers and other powered platforms being used by masons.
In spite of the variety of the equipment used by masons, several issues have persisted regarding the proper use and safety of scaffolds. The first issue involves the fall exposure that masons have while constructing a brick wall. The federal Occupational Safety & Health Administration, OSHA, standards recognize this issue and in 29 CFR 1926.451(g)(1)(vi) specify that “Each employee performing overhand bricklaying operations from a supported scaffold shall be protected from falling from all open sides and ends of the scaffold (except at the side next to the wall being laid) by the use of a personal fall arrest system or guardrail system.” While clear in its intent, there are still people who do not understand this. Simply stated, we allow the mason to be exposed to a fall hazard. That’s right, the mason can fall over the wall if he so chooses. However, any reasonable mason understands that if he leans over too far, he will fall over the wall! Typically, masons like to lay brick at waist high which means that the wall acts as the guardrail—problem solved. In those instances where the wall is lower, then yes, there is a fall hazard. But the hazard of trying to work through a guardrail system laying brick frankly is a greater hazard. Please note that only those who are “performing brick laying operations” are allowed to be exposed to the hazard. In other words, if you aren’t laying brick, you can’t be there.
The second issue involves the use of side and end brackets (commonly, and incorrectly, called outriggers). The normal use of these brackets is on the front of the scaffold, between the wall being constructed and the scaffold front leg. These brackets support the plank for the masons and are moved up in convenient increments as the wall increases in height. There’s nothing wrong with this installation. The problem is when masons install these brackets on the back of the scaffold and then used them as a landing or storage platform for brick and mortar. This is not good unless these brackets have been designed for that purpose. In fact, OSHA addresses this issue in 29 CFR 1926.452(c)(5)(iii) by emphatically stating that these brackets shall be used to support personnel “unless the scaffold has been designed for other loads by a qualified engineer.” The reason for this is that it is easy to overload the brackets and also easy to tip the scaffold over, nether prospect being very appealing to the mason. Keep in mind that the standard doesn’t say you cannot do it; if you would like to do it, hire an engineer who can help you.
The third issue that appears on occasion has to do with the material on the scaffold platforms. There is another OSHA standard, 29 CFR 1926.250(b)(5), that “Materials shall not be stored on scaffolds or runways in excess of supplies needed for immediate operations.” A quick read of this standard would suggest that a mason could have no more than a few brick or block on the scaffold at any given time. In fact, OSHA even issued a Letter of Interpretation that stated that all materials had to be removed from the scaffold at the end of the day. Fortunately, OSHA clarified this letter and stated that the hazards being addressed by this standard included falling objects and scaffold overload. OSHA concluded that since these potential hazards are specifically addressed in the scaffold standards, while leaving materials stored on a scaffold may be a violation of 29 CFR 1926.250(b)(5) it shall be considered a de minimis violation, one that carries no fines. Of course it is assumed that the mason will make sure the brick and block will not fall off the scaffold and the scaffold is not overloaded. This particular issue has appeared recently on jobsites where the Army Corps of Engineers regulations, EM 385, are enforced. As with all standards, it is important to know what the intent of a particular standard is and what hazard is being addressed. Once this is understood, it is much easier to resolve any issues regarding the storage of materials.
As long as we have brick and block walls, we’ll have scaffolding. Scaffolding has proven to be effective and safe, provided you know how to use it safely. Do you?
January 1st, 2012 by David H. Glabe, P.E.
A stimulating and thought provoking discussion addressing safety concerns with scaffolding.
2012 will be an interesting year with the economy, presidential elections, wars, and unemployment weighing heavy on our minds. In an effort to keep your mind off these depressing subjects, I thought it would be a good idea to focus on what you enjoy—scaffolding! Well, it beats thinking about the economy tanking and besides, this is a magazine for scaffolding and access.
Have you ever wondered what would happen if everybody was perfect? Scaffolds would be perfectly constructed and perfectly used by perfectly trained employees. Now there’s something to think about. Just think of the ramifications. No angry jobsite safety monitors; no OSHA citations; no injuries; no deaths. I wonder what that would do to the unemployment figures.
Why do people like to misuse and abuse scaffold components? Take knee-outs and brackets as an example. Why do erectors think knee-outs will support ten tiers of scaffold on top of them and why do users think brackets will hold a mountain of block and brick?
What would happen if we had no OSHA standards? Would injuries and deaths increase, stay the same, or decrease? What would the industry do? What would you do? Would you do anything differently? What if there were no compliance officers? Would it make any difference to your behavior? Why do we not have one set of standards for the scaffold and access industry in this country? For example, are the states so unusual that we have to have different standards in California and Michigan? Why did Washington State rewrite the federal OSHA standards in a “friendly” prose? Apparently nobody in Washington understood that the standards are not instructions but rather are minimum, enforceable requirements.
Why did the Army Corp of Engineers write a separate scaffold standard somewhat modeled after the federal regulations but yet sufficiently modified so that it is extra confusing? It would almost seem that scaffolding and physics mutate into strange creatures from state to state and agency to agency. This could get scary!
Why do we equate longevity with expertise? You know, just because you have been doing something over and over doesn’t make it right. And the opposite is true; how can a person fresh out of school be a consultant? And then we have someone on TV who said: “I’m not stupid you know, I just don’t know stuff.” Is there a way in 2012 to get scaffold users to know more stuff and increase their expertise?
Why do general safety consultants who have never erected a scaffold think they know more about an erection than a scaffold erector? Why do some scaffold erectors think they are exempt from the accepted safety practices? Why is everybody an expert in fall protection and scaffolding? How can a compliance officer, fresh out of school, understand the 28 subparts of the OSHA Construction Standards? Why do compliance officers get minimal training in scaffolding?
Why is the American Society of Safety Engineers the secretariat of the ANSI scaffolding standard and not the SIAI? And here’s something to really ponder: Has anyone measured the cost/benefit ratio regarding the extensive and some may argue oppressive, government intervention in the scaffold industry?
What will 2012 bring for you? I wish for you a prosperous, enjoyable year and you experience a year of good health free of injury.
December 1st, 2011 by David H. Glabe, P.E.
A practical explanation as to the relationship between the OSHA standards, enforcement, compliance and safety in the construction industry.
It’s been a long time since I first became involved in the business of scaffolding. My experience has included a lot of scaffolds, a lot of places and a lot of people. It has also included a lot of regulations. As a blossoming young engineer, I still recall asking by boss how OSHA fit into the design of scaffolding. Since federal OSHA was just a couple of years old at that time, he responded with a clearly stated: “I don’t know.” Forty years later, it appears that we still don’t know how OSHA fits into the design, construction and use of scaffolding. To be fair to federal OSHA, it doesn’t appear that any regulations, standards, codes or guidelines fit into the design of scaffolding. Now, before you get yourself all wound up, this may be somewhat of an extremely broad statement. But think about this: We have standards regarding fall protection and more specifically guardrail systems. In my research I have found guidelines regarding guardrails going back to the 1920’s, almost a century ago. And we still have people designing, constructing and using scaffolds without fall protection. If nothing else, we have consistency.
So what’s the problem? Is it poor enforcement? Is it poor training? Is it poor knowledge? Is it ignorance? Or maybe we just don’t care. Being a Professional Engineer, and accepting the responsibilities that go with the privilege, I am obligated to comply with the myriad of regulations, standards and codes that apply to the profession. Not to do so will result in the loss of my license and opportunity to earn a living. I don’t state this because I think I am special, but rather qualified professionals (degreed and licensed or not) accept the obligation that is or should be expected in the business. I don’t agree with all the regulations; for that matter I’m not really keen on any of the regulations—it certainly stifles constructive creativity. In fact, regulations are insidiously invading all aspects of our lives, resulting not only in a dumbing down of the industry but also in an erosion of expertise, efficiency, economy, and productivity.
Of course, those tasked with the enforcement of these regulations smugly point to the results of their policing actions. They publish yearly results of their efforts as if those efforts have any real effect on the industry. Frankly, the annual OSHA list of the top 10 violations has no relation to the degree of danger involved in the infraction. For example, scaffolds always show up in the top ten, suggesting that there is a real problem with safety in the industry. But is there a problem? Perhaps scaffolding shows up so frequently because infractions are easy to spot and the compliance officers haven’t been trained to evaluate where the real hazards are.
One of the favorite activities these days is the harassment of professional scaffold erectors (casual erectors, where the problems really occur, seem to be immune.) Statistics indicate that the death rate of professional erectors is extremely low, particularly when compared to the 80 annual deaths that occur with scaffold usage, the deaths in construction and more dramatically when compared with the approximately 37,000 people killed on the highways each year.
The situation is becoming so ridiculous due to what I think is a growing hysteria about safety and the lack of understanding of the actual hazards. Enormous amounts of time and energy are uselessly spent deciding whether a regulation has been violated instead of investing in the safe productive work that should be happening. How many times have you sat in a meeting ascertaining whether there is compliance with the regulations? How many hours have been wasted bickering about the nuance of a regulation instead of determining how to get the work done safely?
I am not advocating the abolishment of enforcement but something has to change. It is absolutely amazing how people think they are experts in erector fall protection, for example, and yet have never erected a scaffold in their lives. And yet we give them the authority and take it away from the people most affected. Furthermore, it is stunning to me how many government agencies, construction industry organizations, unions and engineering committees feel compelled to propagate more and more regulations, many applying to scaffolding, and yet do not even bother contacting the Scaffold and Access Industry Association or the Scaffold Shoring and Forming Institute for input. Are you aware that the American Society of Civil Engineers has a code regarding construction loads which includes specifications for scaffold loading? I didn’t think so.
I can sure complain about the problem but unfortunately I don’t have a snappy quick solution. We cannot abolish decent standards and codes nor can we abolish enforcement—those are needed for those employers and employees who just don’t get it. But we do need to abolish the politics in safety. Have you ever wondered why we chase after the employer but not the employee? Me too. Have you ever wondered why compliance officers don’t receive sufficient training for the task at hand? Me too. Have you ever wondered why so many designers and constructors erect scaffolds without having any clue as to what a safe scaffold is? Me too. Have you ever wondered why we allow the sale of scaffolding in this country without any idea of its load capacity? Me too. Have you ever wondered why safety consultants have such a poor understanding of the true hazards in scaffolding? Me too.
Forty years ago we were killing and maiming scaffold users. We’re stilling doing it today. And I still don’t know how OSHA fits into the safe design of scaffolding. However, I do know what a safe scaffold is. Do you?
November 1st, 2011 by David H. Glabe, P.E.
How to determine if the scaffolding you have is in good condition or whether it should be scrapped.
Is your scaffold any good or has it seen better days? While it would be nice to always use fresh out of the box (so to speak) scaffolding, the reality is quite different. Scaffold components are used for many years, showing their age with each succeeding season. How bad can the equipment get before it isn’t any good anymore? How much rust is permissible? How many dents and dings can we tolerate before it’s time to pitch it in the dumpster?
Since scaffolding isn’t free, although some suppliers may think they are giving it away, it is important that scaffold parts are not discarded before their useful life has ended. After all, parts is parts. On the other hand, it would not be prudent to use scaffolding that cannot function as expected. What exactly determines whether a scaffold component is no longer useable? For some components the answer is easy. If a suspension rope has too many broken wire strands it’s time to throw it out. If a suspension hoist has worn internal parts, it’s time to replace them. If the motor doesn’t run, it should be obvious that something needs to be repaired. But what about more subtle problems such as rust; how much rust is too much? Should a scaffold frame, for example, be discarded because it has a rusty appearance or should it be kept in inventory, and rented, until the rust goes all the way through the tube wall? To answer those questions, it is best to understand what the hazards are.
Strength, fit, and alignment can be used to determine the worthiness of a scaffold component. Strength is affected by a variety of factors. For example, a cracked stirrup on a two point suspended scaffold would not be good. Is it necessary to say that maintaining scaffold component strength is important to the integrity of the completed scaffold? Well it is. Consequently, any condition that affects the strength of the component is not allowed. So, what precisely gives a scaffold its strength? Let’s take a look at a supported scaffold, a scaffold that utilizes tubes for vertical support. The material that is used for the tube is one parameter that dictates strength. Any action that adversely affects the properties of that material is not good. For example, excessive heat will affect the molecular strength of the steel and therefore must be avoided. The shape of the tube is important. Any action that changes the shape of the tube will adversely affect the carrying capacity of the tube and therefore must be avoided. This includes kinks, bends, distortion, flattening and stretching of the tube.
Decreasing dimensional changes in the tube wall thickness can never be a good thing. This typically occurs through rust and corrosion although it can also happen through chemical deterioration (such as acids) and through galvanic/electrolytic action. The question of course is how much corrosion is too much? It should be obvious that if you can look through the wall of the tube and see daylight on the other side, you have a problem. Basically the concern is whether the tube has lost too much of its material. Surface rust is harmless. Pitted surfaces are another story. It is difficult to get complete consensus on the amount of pitting a tube can experience because evaluation is rather subjective. Additionally, scaffold tube wall thickness varies depending on the type of scaffolding. The wall thickness can be as little as 0.09 inches (2.3 mm or 3/32”) to more than 0.154 inches (3.91 mm or 5/32”). If you have 1/32” (0.8 mm) pitting on a tube that has a wall thickness of 0.09” (2.3 mm) and you just lost a third of its material. On the other hand, if you have a tube wall that is ¼” (6.35 mm) thick, you just lost 1/8 of its material. It looks like the amount of permissible corrosion is based on the dimensional properties of the tube in question. You may want to consult a metallurgist if a large inventory is under suspicion.
Dents and kinks in tubing decrease the strength of the component. While a flattened horizontal tube in a scaffold frame will decrease the capacity it isn’t that big a deal if it is not the load bearing top ledger. On the other hand, if the dent is in the leg or top ledger it can be a problem since it reduces the strength. It’s tough to determine how much a dent decreases the capacity; don’t take a chance, discard it. Kinks will most certainly decrease the capacity of a tube besides throwing the tube out of alignment. Kinks in load bearing members mean discard it unless you have a qualified engineer analyze its worthiness.
Cracked welds are an indication of poor manufacturing or abuse. In either case the component should be discarded unless a qualified and certified welder makes the repairs. (Depending on the pay scale, it may be cheaper to get rid of the part.) Broken welds surely indicate that the component was treated badly unless you bought the item from an unscrupulous dealer in the first place. In any event, the component must be carefully examined for additional damage that was done to cause the weld to break in the first place. If there is rust in the crack or break, this may be an indication of a pre-existing condition, which suggests that someone wasn’t taking care of the product and wasn’t examining it very closely in previous inspections.
Speaking of abuse, splits in tubes can never be good. Splits can occur because of poor manufacturing or because someone tried to fit one leg on top of a larger diameter leg. In either case, the tube is useless and must be discarded. Twisted tubing, while rare, will overstress the material and degrade its strength. Get rid of it. This goes for twisted angles too.
Overall fit and alignment of members are important. Taking a scaffold frame as an example, if it is racked (one leg is higher than the other) or warped (it doesn’t lie flat on the floor) you have a problem. If the frame can be straightened without breaking the welds, go for it. On the other hand, if you bought an inferior product, it may have been manufactured that way and you are out of luck. You will never get the scaffold to be “plumb, level and square” as required by the regulations; you should have bought better stuff.
Look for missing appurtenances such as cross brace locks, wedges, pins, chains and bolts. Make sure the bolts and pins are the correct size and have not been changed to bolts and pins of lesser strength or size. Inspect critical items very carefully. If the item is bent, it may also be cracked. Don’t take chances.
Finally your manufacturer may have guidelines for inspection of their specific products. It would be worth your while to contact them since they should know their products. Also, go to www.ssfi.org for technical bulletins that will be of value to you.
Note: Thanks to SAIA member Alan Kline for his suggestion for this month’s subject.