I recently toured three large scaffold rental yards. I visually inspected their scaffold components for the 3 D’s: defects, damage and deterioration. My evaluations were based on two condition categories: as-manufactured and other-than-as-manufactured. This last category constituted over 85 percent of the pieces I observed, which were either bent, broken, kinked, dented, cut, coated, corroded or a combination of all of these. Granted, these scaffold parts represented what was left-over in the yard after scaffolding in better condition had perhaps already been rented. However, our local building season is currently in a lull, to say the least, so I probably observed the majority of each renter’s total stock. As I walked their outdoor aisles of frames, braces, platforms and accessories, I gave very few grades much above C-plus. For me, that’s just one step before an “Out-of-Service” tag is applied. Except for recent deliveries of new frames and platforms, the rest of their inventory looked like it might have been used to stage Hollywood’s last Armageddon disaster movie. If I had been the competent person (CP) responsible for scaffold safety when a shipment of those scaffolds arrived on my site, I would have rejected it without hesitation. The single condition I found on every scaffolding component I observed at each rental facility was rust and corrosion. Every welded steel end frame or system component had between 50 percent and 100 percent of its exterior surface covered with rust. That observation is what eventually generated this article.

What Is Rust?

“Rust” is a sub-classification of “corrosion,” which is defined as “an electrochemical process, either rapid or slow, in which the composition of a solid (i.e., metal) is changed, reduced or eroded on a molecular level in a reaction with another substance (water or chemical) in the presence of oxygen to form a new substance.”

Most malleable steel alloys are a combination of iron (97 percent) and carbon (1-2 percent) with trace amounts of elements such as silicone, manganese, chromium, vanadium, tungsten, phosphorous and sulfur, depending on the alloy. Rust is a corrosive reaction in which water (H₂0) helps to oxidize the iron (Fe) and to form ferric oxide (Fe₂O₃) and hydroxide ions, essentially removing iron atoms from the original crystalline structure of exposed steel.

It is a common but fallacious belief that “rust stops rust.” This concept is based on the supposition that after the exterior carbon-steel or iron surface is uniformly coated in rust, atmospheric oxygen can no longer combine with the base metal in order to continue the oxidation process. The truth is that rust does inhibits rust, but only for a short period of time. Water vapor in the air penetrates the microscopically porous coating of ferrous oxide, and the oxidation reaction continues.

The American National Standard Institute (ANSI) clearly considered corrosion to be a limiting factor in developing its 2011 Scaffold Safety Requirements standard when it stated in A10.8.4.32: “Scaffolds and their components shall not be used with acids or other corrosive substances, or in corrosive atmospheres except when adequate precautions are taken to protect the scaffold from damage in accordance with the recommendations of the corrosive substance manufacturer and the scaffold manufacturer.”

If ANSI is concerned enough about loss of materials due to corrosion, then so should the employer and his CP. How much do environmental variants, such as acid rain, actually act as “corrosive atmospheres” and accelerate this oxidation? Due to the crystalline structure of the steel molecule, a minute layer of ferric oxide eventually delaminates from the surface forming “scale.” This fracture exposes a “virgin” layer of base metal, where the process will continue, pitting the surface. Eventually, if environmental conditions remain unchanged, all unprotected steel exposed to the elements will simply convert into a pile of ferric oxide. Priming and painting, electrostatic coating or plating, zinc-galvanization and other processes will, to various degrees, help protect steel from this unrelenting corrosion process, but corrosion is inevitable.

The Safety Factor

When I asked several shop managers if either they or their corporate headquarters had produced any criteria on which to base “out-of-service” conditions on their stock due to rust, I was met with looks of incredulity. They said no one had ever asked them that question, but yet no one offered me a reasonable explanation why they had no such criteria. One corporate president even stated, “Rust just doesn’t matter,” explaining that his stock could not possibly corrode enough to create a safety hazard for his clients, as if saying so made it so. As a result, I would presume, as long as the job gets done without any equipment mishap, near miss or failure, the contractor renting rusted scaffolding has no objective method to judge if he is the recipient of scaffolding which has deteriorated beyond the manufacturer’s safety factor, may cause an accident, or create an OSHA violation and fine.

According to his signed rental agreement, a rental client could be back-charged for having damaged ten frames (which the rental firm claims must replaced with new), but he certainly won’t be charged for the additional rust or corrosion created during a two month rental period.

As far as capacity goes, OSHA’s 1926.451(a)(1) and ANSI/ASSE A10.8 both state: “Except as provided in paragraphs (a)(2), (a)(4), (a)(5) and (g) of this section, each scaffold and scaffold component shall be capable of supporting, without failure, its own weight and at least 4 times the maximum intended load applied or transmitted to it.”

ANSI goes on to state in A10.8(4.10): “Any scaffold damaged or weakened from any cause shall be immediately removed from service and shall not be used until repairs have been completed and approved by a qualified person.”

In other words, if a manufacturer rates a scaffold system as being capable of supporting 50 pounds per square foot (psf) of load-bearing planking, then (depending on a number of variables) it shall withstand 200 psf without failure when manufactured. On the day it is first shipped, the scaffolding is exposed to potential damages. As time passes and site conditions vary, it is up to the employer (and his CP on site) to evaluate every piece of his owned or rented scaffolding to ensure this safety factor is maintained.

The formula to calculate the scaffold’s safety factor (SF) is:

Safety Factor (SF) = L_U / L_A.

In this equation, L_U equals the “ultimate load,” or the total load achieved immediately prior to failure mode. It’s derived by multiplying the safety factor (SF) by the “allowable (rated) load” (L_A). L_A is the maximum total load recommended by the manufacturer and is derived by dividing the ultimate load by the safety factor.

If you know two values, you can always calculate the third. If there is measurable deterioration due to excessive corrosion, according to the CP, then the maximum intended load may be reduced proportionally to maintain a 4X safety factor, regardless of what the manufacturer’s original rated load might have been. But who knows how to competently perform such a calculation?

When I asked my professional engineer on retainer if he could provide me this service, he declined without hesitation. When I asked why he refused, he said the mathematical variants involved with corrosion were infinite. He had, however, no hesitation in running a formula to locate a spot to drill (remove material) a hole to place a single fall protection anchor in a wide-flange beam. This 4X minimum safety factor for all supported scaffold systems and components was established by the American National Standards Institute’s Scaffolding Safety Requirements (ANSI/ASSE A10.8-2011) and is intended to account for, among other items, the scaffold’s age, environmental exposure, and extent of use (or abuse) over its lifetime. Sooner or later, the employer or his CP must decide when the safety factor cannot be guaranteed.

How Much Corrosion Is Too Much?

When it comes to the subject of rust on steel and corrosion on aluminum scaffold components, the CP’s judgment is apparently, out of necessity, going to be subjective. But there are some relevant facts to consider. Fact: No governing agency with jurisdiction and authority has established any limit value to the loss of material thickness on scaffold components. Fact: The employer and his competent person are both responsible for removing scaffolding from service if it is not capable of maintaining an adequate safety factor under load. Fact: If a civil lawsuit arises from a workplace scaffold accident, the lawyer for the injured plaintiff will subpoena both his client’s employer and his competent person for trial testimony. It would be expected in such a trial that the competent person for scaffold would defend his/her competency by producing adequate documentation of qualitative inspections and quantitative evaluations.

The following comments were excerpted from a 2011 article by Mr. David H. Glabe, PE, titled “How to Determine if the Scaffolding You Have Is in Good Condition or Whether it Should Be Scrapped” (www.dhglabe.com/is-it-okay-or-not/):

“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 that 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.”

Glabe’s phrase “never a good thing” will remain in my safety vocabulary from this day forward. Not only is the CP concerned with the exterior deterioration caused by rust, but also any interior tube damage which can occur when frames with open leg tubes are stored outdoors all year. This type of deterioration often displays itself in loose pin attachments, direct ground contact of frames and repeated freeze-thaw cycles during winter months, especially in lots with southern exposures.

In his article, Glabe points out that loss of wall thickness is measurable and therefore quantifiable. A reasonable person might conclude that gross material loss should have a definable limit in order to ensure that the scaffold component is actually capable of supporting its own weight and at least four times the maximum intended load. But that’s not the case.

Measurement and Management

Early in my construction career I learned the phrase, “If your don’t measure, then you can’t manage.” I personally believe this is true in the case of scaffold rust and corrosion. If I were to attempt to measure rust or corrosion on a scaffold frame in the field (rather than a certified testing laboratory), there are three tools I might consider using:

1. Fiberscope:This battery-powered, hand-held fiber-optic device has a flexible, tip-articulated, goose-neck LED lamp and video camera capable of giving the inspector a view of the interior condition of a leg tube, limited only by its operating length (up to 128 inches).

2. Digital micrometer-caliper:An electronic instrument to measure overall tube diameter as well as the material thickness (from 0-6.0 inches) at either end of tube, where wall corrosion would reasonably be most prevalent.

3. Digital depth gauge:An electronic thin pin-micrometer used to measure the depth of pitting and scaling below the original surface of a scaffold tube.

Some contractors might argue that this level of precision instrument inspection would not occur on a typical construction site, and they would probably be correct. However, that doesn’t mean that the situation should be acceptable. 

A tube wall that has lost a significant portion (let’s assume 25 percent) of its wall thickness cannot be expected to react as dependably as a tube that has only lost 1 percent thickness. The professional engineers I’ve spoken with admit that rust in any amount beyond the “minor” category generally produces failure models which are best described as “random” or “unpredictable,” but no one gave me the criteria to identify “minor” or “insignificant” rust.

One might also reasonably ask: If the scaffold designer initially specified a minimum tube wall thickness for the fabricator to use, why wouldn’t it be reasonable to specify the minimum loss-of-wall-thickness for a competent person to use as “out-of-service” criteria? If the tube stock can be too thin to begin with, why wouldn’t there be a minimum thickness due to corrosion?

If there is no “good-faith” attempt made by the employer’s competent person to, in some manner or method, quantify and document the structural quality of the scaffold equipment (as is done in a rigging inspection), I am not convinced anyone could claim they were actually competent to inspect scaffolding according to 1926.451(f)(3). After all, a “no-go gauge” is used to inspect the body diameter of each link by inspectors of chain rigging. The amount of permissible lateral and longitudinal deflection on rigging hooks cannot exceed predetermined angles. The percent of elongation of a synthetic web sling is measured to determine its capability to function as designed. Unfortunately rigging inspection, like scaffolding, also has a number of unquantifiable defects, including how much surface fiber fraying (fuzzing), breaks in edge-stitch threads or discoloration of the nylon fabric can be considered a practical service limit value. At some undefined point of degradation, any of those conditions may be cause for taking them out of service.

Inspection Guidelines

A scaffold may consist of either a single, two-frame lift 4 feet high used to paint a ceiling. It could also be the 2,100 tubular aluminum frames which were freestanding 310 feet high around the Statue of Liberty, withstanding 100 mph winds for three wintry months in 1984. On that job, how much deterioration of aluminum tubes due to salt oxidation would have been considered “acceptable loss” by Tom Crisci, CP supervisor for Universal Building Supplies, Inc., who erected it? The competent person’s subjective experience and training may ultimately have to suffice in order to make that decision.

Many manufacturers and industry groups, such as the Steel Scaffolding and Shoring Institute, Scaffold and Access Industry Association and Scaffold Training Institute, promote their own trade-accepted guidelines for the scaffold erector and user, some of which state:

• Inspect all equipment before using.

• Keep all equipment in good repair.

• Never use any equipment that is damaged or deteriorated in any way.

• Heavily rusted or corroded scaffolding equipment is a telltale sign of abuse or neglect.

• Always avoid using rusted equipment as the ultimate strength and stability of such equipment cannot be known.

Obviously, rust and corrosion on scaffolding are serious factors to these professionals. Any component in a scaffold system which has deteriorated such that it is no longer capable of supporting 4 times the manufacturer’s rated load must be taken out of service and tagged “Do Not Use” by the competent person for scaffolding.

In reality of construction work, when attempting to avoid using rusted equipment may prove difficult when it could directly interfere with the employer’s productivity and profit. But when it comes to scaffolding, deterioration due to rust or corrosion anywhere throughout a system containing hundreds of individual components could lead to a catastrophic structural failure — without a visual warning prior to a disaster. So the question everyone should be asking themselves before they access the first level of scaffolding is, “How much rust is too much rust?”

I have been told by everyone I’ve asked that it’s an excellent question but, regrettably, one without a definitive answer. The CP typically uses a checklist to evaluate the operable condition of each and every subcomponent, and scaffolding should be no exception. For instance, the CP may inspect a welded steel end-frame for the following items:

• Straight and square (both legs sit evenly on slab)

• No racking (lays down flat on slab

 • Frame pins straight and locked in standards

• Tubes free from splits, nicks, cuts and holes

• Tubes free from dings, dents, bends and twists

• Welds intact without visible cracks or crazing

• No missing/damaged appurtenances (locks, frame pins)

• No visually opaque finish or coating on surfaces.

• No rust or corrosion affecting structural strength.

• Manufacturer’s decals/labels in place and legible.

Before checking off the last three items, the CP must first make some tough decisions. The individual who has assumed the employer’s CP obligation to provide a workplace “free from recognized hazards that are causing or are likely to cause death or serious physical harm” to the co-workers in his or her charge can only evaluate the tools and equipment they are to use as “free from recognized hazards” based upon the condition in which they were manufactured. A relatively new frame with some nominal paint scratches with surface rust on the top of the bearer bars resulting from normal wear over a brief period of use might be approved as “close to manufactured-condition.” But when a totally rusted, 20-year-old frame which has been dropped to ground numerous times during disassembly is compared to the relatively new frame, it would be clear that its observable condition was well beyond a reasonable service-life limit.

At this moment all across the country, rusted scaffolding is being erected, accessed and loaded without collapsing. To a competent person, that is not proof that “rust doesn’t matter.” Sometimes the decision to tag equipment “Out-of-Service” is not easy to make, in which case I recommend my own prime directive: When in doubt, tag it out.

 In this and every inspection evaluation, the CP is always representing the best-judgment criteria as defined by his employer in his Safety Program, as well as his or her personal ethical values. One CP may take a frame that shows significant scaling and pitting out of service, while another may decide it is compliant and safe to use. Either way, it’s crucial for the CP to develop and use a system of evaluation criteria, albeit subjective, to support the decision.