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Construction Safety

How "Safety Symmetry" Provides Clues to Safe Sites or "Why Is That One Cow Standing?"

TJ Lyons | December 1, 2012

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A construction site

Growing up on a dairy farm, I learned that routine and order were important and that walking in a pasture at night was a bad idea. Cows are particular and true creatures of habit. So, late at night, if a cow was standing around the pasture while her friends were all sleeping (every nose upwind), something was out of order, and often the problem was with that particular cow. This column is based on the principle that you can use the appearance of symmetry to make sure those performing construction work are competent and the systems they use are safe—by looking for that one standing cow.

Cranes, scaffolding, and rigging are all capable of suspending huge loads or supporting dozens of workers safely, and each depends on the close interaction of other materials. Though mechanical failure is rare on a construction site, when something important fails, the results are often catastrophic. As you walk your project sites, first take a broad look at everything, and then focus on the little things that make the big things work, for comparison is one of your most valuable tools.


During a site walk, I saw hundreds of wooden timbers being driven into soft coastal soil by three mammoth pile drivers. All were making a racket and puffing out those unique jets of steam and smoke from between the hammer and that little wood cap that always appears out of place. As I looked closely at the rigs, from a distance, each was in great shape with no excessive smoke indicating an engine concern, and the leads hanging from the hammer were all well secured to the latticework. My first glance provided some initial information—good equipment, each rig orderly in appearance. As I approached the rigs, I looked at the connection between the load and wire rope—the wedge socket. Two of the three had the wedge-sockets reeved correctly, but the third was different. I instantly recognized something was wrong—and a simple comparison provided a great correcting conversation.

Wedge-sockets are unique connections that rely on perfect assembly and "wedging" the device to secure the load and wire. Based on past experience, I knew the odd wedge-socket (the standing cow in the pasture) was wrong but also recognized three competent persons running each of the rigs who should have caught that. I called over the rigging boss and rather than tell him to shut down the rigs I said "So, years ago I found one of these reeved incorrectly, and I cannot quite remember what the problem was. Take a look at these. Why is that one wound the other way?" There was no accusation, and his authority was not overridden by an amateur. Now he would need to make the decision to shut down the rigs on his own. The opportunity for comparison avoided the confrontation. Ultimately, he returned later to thank me, acknowledging one of the wedges had been installed incorrectly, and later I even got a thumbs up from that operator. To his credit, the super called all the operators and helpers together and reviewed the error before making the correction because he was able to show what right and wrong looked like.

Figure 1: Incorrectly Reeved—Nonsymmetrical and Clumsy Appearance

Incorrectly Reeved—Nonsymmetrical and Clumsy Appearance

Figure 2: Correctly Reeved Wedge-Socket—Symmetrical

Correctly Reeved Wedge-Socket—Symmetrical

Here are some tips on wedge-sockets:

  • If they are reeved incorrectly, they can fail. They must be assembled perfectly.
  • It is human nature to attach loose things to solid things, but not in the case of wedge-sockets. The dead end (no load) or "tail" end of the line must always be free. The previous photo shows a clamp that "grips" only on the live side of the line—made just for that connection, allowing the dead end to stay in place but allowing the wire to work unrestricted.
  • Pay attention to the "tail" of the wire rope to ensure it is long enough, terminated perfectly, and never tied off to the live end of the line, or the wedge won't wedge because it's restricted from moving.
  • If the top line of the wedge-socket is not level, something is usually wrong.
  • Cable clamps and wire rope should never touch. Wire can touch wire (that's how it's stored on the drum), but when cable clips rub on wire rope, the rope is damaged.

Figure 3: Correct and Wrong Wedge-Socket Installation

Correct and Wrong Wedge-Socket Installation

Tower Crane Inspections—Using Lack of Symmetry as a Clue

Though cranes are the most dangerous of any equipment on a work site, tower cranes, if erected and well maintained, provide a welcome level of safety. As disasters have confirmed, cranes and their rigging must be perfect.

During one audit, I noted that the operator had built a wooden shelter around the cab for warmth. My concern was the security of that material but also whether there were enough fire extinguishers for the additional combustible threat way up there. The crane had been inspected by the city and approved. As I climbed to meet the operator (238 feet up), I took breaks at each level to avoid passing out and inspected the connections to look cool to those watching from below. I soon noticed some of the bolts had a nut/bolt/flat washer or washer/lock washer, some had a nut/bolt/flat washer, and one level only had nut/bolt, no washers. This simple lack of symmetry raised a red flag as I climbed.

Figure 4: Lack of Symmetry in Nuts, Bolts, and Washers

Lack of Symmetry in Nuts, Bolts, and Washers - TopLack of Symmetry in Nuts, Bolts, and Washers - Bottom

After completing the climb to the top and speaking with the operator, I called the city's crane engineer, who I knew, and explained my concern. He immediately agreed that each bolt should have the full complement of flat and lock washer, regardless of the connection. The crane was taken out of service until a technician from the firm agreed that the repairs should and could be completed due to the two-bolt connection, but the crane could not be used until the corrections were made.

When inspecting anything that is connected, make sure each connection matches the manufacturer's assembly requirements.

Scaffolding—Symmetry by Design

If there was an award for safety symmetry on construction projects; scaffolding would always win. Conventional scaffold relies on the transferring of a load (energy) through each scaffold component to the ground. In the case of scaffolding, one weak (or bent) portion can cause catastrophe, so perfection is a must. In many cases, scaffolding is poorly constructed, providing significant risk to the users. Many will scream and admonish me by email for that statement, but having inspected over 500 sets of scaffolding, I would estimate 80 percent were not perfect, and most of my peers would agree.

Look at great scaffolding from a distance. It is a combination of angles and lines that is orderly, pleasing to the eye, consistent, and symmetrical. Scaffolding is one of the unique systems that, when failure occurs, the system fails—so eliminating every potential contributor is critical beginning with the first connection.

Correct Scaffolding

Correct Scaffolding

Contributors to Unsafe Scaffold Erection

There are several contributing factors to improperly assembled scaffolding.

Flexible connections. When I was working years ago in Northern California, scaffold erection had fallen to such a low level of quality that sections were often wired together, even though levels of 10 stories were achieved. While we will discuss several of the contributors behind this shoddy construction, the lesson of using safety symmetry to search for unsafe connections is worth exploring. For example, when you see wire used on scaffolding, that's a red flag. Connections must be solid. The manufacturers certainly don't recommend wiring their system together if things don't fit properly. After a collapse, when the Occupational Safety and Health Administration and the attorneys show up and spot the use of wire used to hold the scaffold up, someone will undoubtedly pay big time.

Lack of design. In many cases, the erection firm will send a load of scaffold sets and planks to a project, and the assembly foreman will try his best to make it fit. That is like buying shoes for someone else. Each building has its own unique requirements, and trying to match scaffold to the structure is an area where critical failure can occur.

Bastard bays. One common hazard produced by lack of design is the "bastard bay." Scaffold frames are a "set," each component of a standard length, engineered for attachment to another, typically by a connection secured by a pin. If the connecting span is 10 feet and the last run to cover is 10 feet 1 inch, you cannot connect the components on the first level—and each level from there up. This one error will provide a fault in the energy transfer that the manufacturer designed into the system. In the example shown below, the crews simply wired the connections together. This provides a weak link in the entire system and an unsafe railing. You will often find that lack of planning in scaffold construction is the root of the unsafe contributors, but back to symmetry.

Unsafe Railing

Unsafe Railing

When you spot a bastard bay, always stand inside the scaffolding, and look up. In almost all cases, adjustments will be made to "fit" the scaffold to the structure, creating unanticipated openings in the walking surfaces. If you see an engineered systems of solid and symmetrical connections (and no cows are standing out), you have a great set of scaffolding. If you see odd angles, proper planning did not occur, and you have a problem.

Scaffolding with Problems

Scaffolding with Problems

Wire and flexible connections. When a system is held together by wire, it's already failing. In the photo below, the erector chose to make this connection with wire. Since wire has no known capacity to take a load (it secures, not supports), the connection is likely to fail and, just as important, is prone to slip. This shoddy connection was found supporting a six-story scaffold, and it was immediately taken out of service. Those operational implications and schedule creep cost well over $40,000 thanks to one incompetent person.

Leonard Mlodinow said in his book, A Drunkards Walk: How Randomness Rules Our Lives, "The chances of an event depend on the number of ways in which it can occur," confirming that every contributor (such as wire on scaffolding) matters. Add too much weight, or perhaps a blow to the base from a passing forklift truck, and a well-assembled system may survive; but a failing one will not.

Wired Scaffolding

Wired Scaffolding

The last bit of symmetry to look for on a scaffold starts at the base. Each upright must be solid and work perfectly or, like a sore foot, it won't take your load, and weight is shifted elsewhere.

Unsafe Wired Base

Unsafe Wired Base

Some additional clues safety symmetry provides when examining scaffolding:

  • Wire used to secure the uprights to anything indicates an unsafe system.

Unsafe Wire Usage

Unsafe Wire Usage
  • Scaffold sections removed to access the work face indicates a compromised system.

Compromised Scaffold System

Compromised Scaffold System
  • Is the scaffold based well supported? If not, it is an unstable system.

Unstable Scaffold System

Unstable Scaffold System
  • Does it look like there is more than 12" of adjusting screw showing? Though not always the rule, this is a great place to find base supports that exceed their allowable height.

Base Supports Exceed Allowable Height

Base Supports Exceed Allowable Height
  • If there is equipment moving in the area, is there a barrier protecting the scaffold from getting hit from passing equipment? Look for tire marks to confirm that hazard.

Lack of Barrier Protection for Scaffolding

Lack of Barrier Protection for Scaffolding
  • Does anything appear crooked (asymmetrical), confirming something has failed or is failing?

Asymmetrical Scaffolding

Asymmetrical Scaffolding

There are plenty of other areas to scrutinize, but those mentioned will provide specific focus on the strength of scaffold systems

A tip: Inspect any set of scaffolding after the first level is built. Work with the competent person and get the foundations right, and you will have a beautiful system in place. If you inspect the final set of scaffolding and find an error on the first level, that hazard will be installed at each additional level, and corrections at this point are very costly.

One of the best tips I ever captured was from having conversations with the competent person erecting the scaffold. If you spot a concern and he/she steps back while looking at the scaffold and says, "Well you tell me what's wrong," that's not the person you want doing the work.

Use your eyes and the order of things to get a feel for how things are assembled on your site, and you will find not only where to focus, but also things of beauty—safety symmetry.

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