Posts Tagged ‘aerial lifts’
March 25th, 2012 by David H. Glabe, PE
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.
September 1st, 2011 by David H. Glabe, PE
An appraisal of the codes and standards that apply to aerial lifts, including boom lifts and scissors lifts.
Sometimes it’s simple, sometimes it isn’t. When it comes to aerial platforms, such as boom lifts, scissors lifts, mast climbers and the like, the applicable OSHA standards get twisted, misapplied, and misused. What causes this, you ask? Well, maybe you don’t ask, but here it is anyway!
First a little history: When OSHA decided to revise the Construction Industry scaffold standards, it was determined that aerial platforms (OSHA calls them aerial lifts), would be included. Since aerial platforms are a very specific type of scaffold, OSHA acknowledges this fact by clearly stating in the Scope and Application [29 CFR 1926.450(2)] that “The criteria for aerial lifts are set out exclusively in §1926.453 of this subpart.” To further emphasize this exclusivity OSHA restates the obvious in the General Requirements, §1926.451, stating that “This section does not apply to aerial lifts, the criteria for which are set out exclusively in §1926.453.” What all this means is that none of the scaffold general requirements, including fall protection, access, platforms, and falling object protection to name a few, apply to aerial platforms.
In theory, for aerial platforms, all of this information is contained in §1926.453. And this, in my opinion, is where the confusion begins. §1926.453 references an American National Standards Institute standard, ANSI A92.2-1969. Furthermore, OSHA describes the equipment it considers to be an aerial lift:
(i) Extensible boom platforms;
(ii) Aerial ladders;
(iii) Articulating boom platforms;
(iv) Vertical towers; and
(v) Any combination of any such devices.
The 1969 in the standard is the year 1969. This was the current standard when the scaffold standards review began. Consequently this is the standard that was used to establish the definition for an aerial lift. And therein lays the problem since there has been a substantial growth of aerial platform types since 1969. Fortunately OSHA recognized that new types of aerial platform equipment and ANSI standards have been introduced into the market since 1969. A note was added at the end of §1926.453 in the OSHA standards that recognizes the ineffective applicability of the 1969 ANSI standard by referring the reader to Non-mandatory Appendix C which “lists examples of national consensus standards that are considered to provide employee protection equivalent to that provided through the application of ANSI A92.2-1969, where appropriate.” Non-mandatory Appendix C lists ANSI A92 Consensus Standards which apply to the aerial platforms that are familiar and common today. Included in this list are familiar aerial platforms such as “Boom Supported Elevating Work Platforms” and “Mast Climbing Platforms.”
In practical terms, the referenced ANSI A92 standards are the best resources to use to ensure safe use of aerial platforms. In fact, a review of OSHA §1926.453 will quickly illustrate the deficiencies of OSHA §1926.453. This is said not to criticize the OSHA standards but rather is a statement of fact concerning the limitations of the OSHA standards regarding aerial platforms and the legal restraints that often stifle standards writers’ efforts. The ramification of all this is confusion! Interestingly, the scaffold General Requirements, §1926.451, are frequently cited as applicable to aerial platforms. This is incorrect although common practice would indicate otherwise. Additionally, OSHA §1926.452, Additional Requirements Applicable to Specific Types of Scaffolds, does not apply since aerial platforms are “exclusively set out in §1926.453.” Clear to me; clear to you?
In legal or perhaps technical terms the outcome of standards application is a bit different. This shows up in an OSHA Letter of Interpretation that opines that “Self Propelled Elevating Work Platforms” (ANSI A92.6), commonly known as scissors lifts, are not aerial platforms/lifts but rather “Mobile Scaffolds.” Due to the constraints and wording of the language in §1926.453 and the ANSI A92.2-1969 standard, it is argued that scissors lifts are not included in the ANSI A92.2-1969 standard. Thus, scissors lifts are not aerial platforms/lifts. If they are not aerial platforms/lifts, they must be something else. I guess since a scissors lift has an elevated platform and it has wheels, it can be concluded that scissors lifts are rolling scaffold towers. Using this logic, helicopters, airplanes, forklifts, Airline Ground Support Vehicle-Mounted Vertical Lift Devices (ANSI A92-7), and boat trailers can be considered rolling scaffold towers!
What’s the bottom line? The scaffold General Requirements do not apply to aerial platforms. The scaffold Additional Requirements Applicable to Specific Types of Scaffolds do not apply to aerial platforms. In spite of OSHA’s opinion that scissors lifts are Mobile Scaffolds, scissors lifts are aerial platforms. After all, I would think the industry should know what their equipment is; I hope you agree.
July 1st, 2009 by David H. Glabe, PE
What does this have to do with temporary structures such as scaffolding, aerial lifts, shoring and formwork? Plenty since the decision by one can have a devastating life threatening effect on others. I’m not being cynical or arrogant; plenty of opportunities lie ahead for me and you as we go about our daily lives. Some of us will learn from these opportunities while some unfortunately will waste the chance to broaden their horizons and deepen their knowledge. They will blow the chance to develop their common sense. There is a saying that goes something like this: Where does good judgment come from? Well, it comes from experience. Where does experience come from? Well, that comes from bad judgment!
If you are the clerk at the local convenience store, chances are that your bad judgment, perhaps based on a lack of common sense, will not cause the death of a customer. However, if you are a scaffold erector your decisions may result in another’s death. This is serious. Frankly, common sense drives many activities in the access and construction industry. Daily decisions are made based on common sense, as they well should. However, there is a fine line between common sense, based on “sound practical judgment,” and irresponsible actions that are just plain unjustifiable. For example, why would a job superintendent not follow the shoring design prepared by a Professional Engineer? Why would a scaffold erector not follow the qualified person’s scaffold plan? Why would a carpenter choose a different formwork member although he has no “specialized knowledge or training” that would enable him to make the correct choice?
This common sense issue goes beyond engineering and construction. Jobsite safety on many projects is held hostage to the phenomenon of poor common sense. Where is the common sense when an employee must utilize personal fall protection while standing behind a properly constructed scaffold guardrail system? Where is the common sense when it doesn’t matter what the user chooses as an anchor so long as she is “tied off?” Common sense has obviously left the jobsite when the safety inspector ignores the advice of a qualified person and instead follows her own ill informed opinion of what is safe. And certainly common sense never arrived at the jobsite when a signed piece of paper magically becomes the critical issue and not the practiced safety it is suppose to imply.
It seems common sense is no longer common. In fact, the situation has morphed into a weird perverse alternate world where qualified workers are no longer allowed to make decisions yet the unqualified worker is allowed to act irresponsibly with no risk of having to accept the responsibility of his actions. Why is it that a worker can modify a scaffold or incorrectly construct shoring without risking the consequences while those who have made the effort to understand the details of the activity are so severely punished, not because of their actions, but only because of their knowledge? How can a shoring equipment supplier be held responsible for the customer’s superintendent’s poor decision when that superintendent didn’t even bother to learn how to use the equipment or even ask for help, help that is free for the asking? Incredible. And yet, those who lack common sense escape the wrath of the attorneys, OSHA and others because they can claim ignorance while those who do have the knowledge and expertise are held under the scrutiny of the legal microscope.
What is the solution? It’s easy. Common sense will tell you that you shouldn’t be involved with work activities that exceed your expertise. The Code of Ethics for Professional Engineers requires that Professional Engineers practice only in their area of expertise. Other professions have similar tenets in their codes. Punishment for a breach can be severe. Why not do the same for the Construction Industry? Make the employee individually responsible for his actions. You don’t comply with the OSHA Standards? You get fined. (Of course, if the employer is misbehaving, she should get fined too.) You make changes to the shoring layout, you are responsible; not the employer, not the designer, not the supplier, you.
Finally, my experience indicates that common sense disappears and intimidation replaces it. In fact, intimidation, not common sense or knowledge, plays a huge role in the decision making process. Safety inspectors can have incredible power over contractors and subcontractors. Challenging a safety inspector’s incorrect requirement on a jobsite often results in the threat of continued harassment leading to trumped up accusations and stipulations that at a minimum wastes money and ultimately never increases safety. Why, for example, would a safety inspector insist that a wall form scaffold bracket that has been safely used for over 50 years all of a sudden be dangerous? Why would this same individual not trust the information that is offered to bolster the facts? Why would the inspector not rely on the statements of numerous qualified individuals or the expertise of the professional consultants? To me it is almost unbelievable that we have allowed individuals who lack any knowledge, or common sense, to dictate the actions of others. I can only say it must be the lack of common sense. Idle requirements without substantiation must stop. Poor work habits that result in dangerous and fatal accidents must be stopped. Common sense will tell you that.
December 1st, 2006 by David H. Glabe, PE
While scaffolds come in all shapes, sizes, and function, they can be categorized as supported, suspended or aerial lifts. The American National standards Institute, ANSI, has defined an aerial platform as “a mobile device that has an adjustable position platform, supported from ground level by a structure.” Scissors Lifts, Mast Climbers, and Boom-Supported Elevating Work Platforms (Boom Lifts) are examples of these machines. While that may explain aerial lifts, what is the difference between supported and suspended scaffolds? OSHA offers a rather detailed description for each but it can easily be explained this way. A suspended scaffold is any platform supported by ropes. That means all other scaffolds are supported scaffolds (if they aren’t aerial lifts). In other words, a two point wire rope suspended scaffold really is a suspended scaffold. However, a frame scaffold hanging off the side of a bridge, for example, is a supported scaffold, even if it is “suspended” over the side of the bridge. While this example may be obvious, other scaffolds may defy easy categorization.
An Adjustable Scaffold is one of those scaffolds. Which standards apply to this scaffold? Is an Adjustable Scaffold a supported scaffold or is it a suspended scaffold? For that matter, what is an Adjustable Scaffold? By definition, an Adjustable Scaffold is “a scaffold structure with a manually elevating carriage that supports work and material platforms.” What confuses the situation is that the platform on an Adjustable scaffold is supported by wire ropes. This would mean that the scaffold is a suspended scaffold. But not so fast; the wire rope is supported by rigid legs. That would make it a supported scaffold! Looks to me like it’s both suspended and supported. Well it is, sort of. An Adjustable Scaffold is classified as a supported scaffold and here is why. It is true that all Adjustable Scaffold platforms are supported by wire ropes. However, unlike the typical suspended scaffold, Adjustable Scaffolds have an additional mechanism, a back-up system if you will, that supports the platform if the wire rope fails. This mechanism includes a mechanical lever that prohibits the platform from falling very far, typically less than 12 inches. Because this mechanism exists, the Adjustable Scaffold is not a true suspended scaffold. That is, if the rope breaks, the scaffold platform will not crash to the ground. Rather, it will only drop 12 inches, terrorizing the occupants but otherwise staying in the air and keeping them safe.
Adjustable Scaffolds are used almost exclusively by brick masons. The ability of the platform to be slowly raised as the brick wall is constructed permits the top of the wall to always be at the optimum elevation for the mason. One of the unique features of some Adjustable Scaffolds is the ability to free stand 28 feet high. This allows the scaffold to be erected to the full height of a “big box” store (e.g. a Home Depot® or Wal-Mart®) without having to tie it to the structure. This is a big advantage for masons in terms of efficiency and constructability. For taller scaffolds, the masts must be tied to the adjacent structure, in compliance with applicable supported scaffold criteria.
As with all scaffolds, Adjustable Scaffolds must have proper fall protection. This usually is a guardrail system that is installed when the scaffold is initially erected. However, when the platform is being stocked by a forklift, and the guardrails are removed, the exposed employees must be wearing fall restraint or arrest equipment attached to a suitable anchor. Since Adjustable Scaffolds are designed for masons, they can support substantial loads. Consult the manufacturer for the capacity of the scaffold you are using. Access can be provided by a portable ladder, stairs, a manufacturer supplied ladder or direct access. Consult your manufacturer if you can use the mast of your scaffold for access.
Adjustable Scaffolds are Supported Scaffolds. TheUSfederal OSHA standards that apply are the General Requirements, 29 CFR 1926.451, including the Supported Scaffold Criteria, 29 CFR 1926.451(c) which addresses scaffold stability and scaffold foundations. Additionally, The American National Standards, A10.8-2001 has consensus standards that specifically address Adjustable Scaffolds.
October 1st, 2001 by David H. Glabe, PE
No assembly required? That’s right. Unload that aerial lift off the truck, hop on and away you go. And go you will – just in ways you may not anticipate. And that is the problem. Too many users of aerial lifts think they are a no brainer to use. They assume there isn’t anything to it. Push a button, pull a stick; how complicated can that be? Well, that’s not the complicated part. To quote the American National Standards, ANSI, for Boom Supported Elevating Work Platforms,
“The operation of any aerial platform is subject to certain hazards that can be protected against only by the exercise of intelligence, care, and common sense and not by mechanical means. It is essential to have competent, careful personnel trained in the intended use, safe operation, maintenance and service of this type of equipment.”
The bottom line is that, as with many types of equipment, it is training and skill that will minimize hazards, not additional equipment. The Federal Occupational Safety and Health Administration, OSHA, has a specific section within the scaffold standards to address aerial lifts. It is 29CFR1926.453. Unfortunately, this section of Subpart L is somewhat inadequate for today’s aerial lifts. Due to circumstances that occurred in the development of Subpart L, it was necessary to reference an old (1969) ANSI aerial lift standard, A92.2-1969, for use as part of the OSHA standard. This standard, written prior to the proliferation of today’s various types of aerial lifts, does not clarify the type of fall protection required for the different types of aerial lifts. The result of this is confusion pertaining to the safe use and operation of aerial lifts. More importantly, it confused the fall protection requirements for aerial lift users. A careful reading of 29CFR1926.453(b)(2)(v) indicates that “a body belt shall be worn and a lanyard attached to the boom or basket when working from an aerial lift.” No distinction is given between a “boom lift” and a “scissors lift.”
Fortunately, OSHA recognized the confusion that existed due to the reference to the 1969 ANSI Standard. OSHA remedied the situation by including the current editions of applicable aerial lift ANSI standards in the non-mandatory appendices of the OSHA scaffold standards. This means that the trained user who complies with the applicable ANSI Standards will be in compliance with the OSHA Standards. Additionally, if the user complies with the manufacturer’s requirements, he/she will also be in compliance with the safety standards.
A review of the ANSI Standards for Boom-Supported Elevating Work Platforms (boom lifts) and Self-Propelled Elevating Work Platforms (scissors lifts) reveals specific fall protection requirements. First, both boom-lifts and scissors lifts must have guardrail systems. Second, all occupants of boom-lifts must use fall restraint equipment to keep them in the basket or fall arrest equipment to catch them if they leave the basket. Third, all occupants must comply with the manufacturer’s requirements for fall restraint/arrest. (Fall restraint is keeping you from falling out of or being ejected from the basket. Fall arrest is catching you after you have fallen out of the basket. Obviously, fall restraint is highly desirable to fall arrest!)
This distinction between restraint and arrest leads us to the issue of body belts. OSHA outlawed, and for good reason, the use of body belts for fall arrest but has still allowed them for fall restraint. Therefore, the reference to a body belt in the standards is correct, provided you are only using the belt for restraint only. Many employers do not make the distinction between belts and harnesses and therefore only allow employees to use full body harnesses. This is an excellent practice since it eliminates any potential mistakes. Furthermore, for restraint to work, only a short lanyard, attached to the manufacturer supplied anchor, must be used. A worker using a six feet long lanyard can still get launched out of the basket. This would not be good.
Scissors lifts, when used correctly, do not have the potential to launch people off the platform. Therefore, a guardrail system is normally considered adequate. However, even in this situation, if the manufacturer of the equipment provides an anchor and specifies in their instructions that occupants must use personal fall protection, then compliance is expected. In other words, not complying with the manufacturer’s recommendations can be construed as being in violation of the OSHA Standards.
If you are a user of aerial lifts, you must comply with all of the manufacturer’s instructions and recommendations. You also must comply with the applicable ANSI Standards. If you use aerial lifts, you should have these standards. In fact, there is no excuse not to have the standards because it is easy to obtain them from the Scaffold Industry Association at a very reasonable cost. As they say, don’t delay, order today; the life you save may be your own!