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NEWS > JULY 2019

Tower Crane Accidents

Let’s Start with the “Why?”

tower crane
Construction of Lakhta Center in St. Petersburg, Russia. Photo ©BackyardProduction | iStockphoto.

by Dennis J O’Rourke CSP

My first memory of a tower crane was a trailer mounted one, all manually operated, self-erecting, located in Ireland. I observed it when on a 1960s vacation. It was helping build a two-story house. Working at Port Canaveral at the time, cranes interested me – I maintained them.

The description “tower crane” is a relatively modern term for the rotating crane soaring above a high rise building under construction. As humankind multiplied, so did the need for taller buildings to keep pace with the cities’ growth – simple as that. Cranes rose higher, and higher, and still higher! One of the tallest buildings in Eastern Europe, St. Petersburg, Russia, is about 1500 feet (462m) tall and built with external free-standing tower cranes.

There is a very logical reason for building “up and not out.” First, it is a more efficient use of the land and utilities. Take this one building, for example: a 1500 foot sewer pipe, top to bottom, can remove the wastewater from more than 350 apartments. The length of the sewer pipes connecting 350 private home extending over 70 acres (5 per acre) would equal miles of the stuff, plus all the roads, walks, cables, etc.

Another advantage of going up is environmental – save the trees; they absorb carbon dioxide. Leaving large tracks of rural unspoiled land is now a priority mandated by some states. Today, trees are looked upon as preferred to be living. And they are not taken for granted; they allow humans to continue living on this beautiful planet of ours.

A SIMPLE MACHINE

Like most mechanical devices, the moment they are built, the manufacturer starts to analyze them, making “improvements” to the next units that are produced, i.e., the serial number emerges. When a customer purchases a crane and starts using it, they provide feedback as to what would make it better on the job site to speed things up and reduce the cost of labor. They talk, and the manufacturer responds. Tower cranes are of a relatively simple design, and have developed quickly to meet the changing needs for the taller building! Thus, cranes are continuously modified, and at a rapid pace it seems.

Older towers were single section towers, but soon construction needed multi-sections that were pinned or bolted together to increase the height that loads could be lifted. These old designs became useless for most buildings over three floors.

A change (in the 1970/1980s or so) to start relocating the tower from inside the elevator shaft (where the floors stabilized the tower) to the outside of the building’s perimeter, ended up, as it turns out, increasing accident exposures to the public in the streets around the construction site. Moving the crane’s location affected two elements of the crane’s design; a longer jib was necessary to reach all the corners of the structure and tie-backs to the building were required for tower support However, this move did open up the elevator shaft that the towers once occupied, thus, allowing work to take place in that area at the same pace as the building’s general progress. Was the trade-off for the opening of the elevator shafts worth it? Sure, if the falling of tower cranes can stop! Now, occurring accidents bring to light the problems of the modern tower.

Another evolving change came when crawler cranes, equipped with a tower attachment and luffing jibs that could safely work at about 250 feet, were replaced with the fixed tower crane erected on site (much cheaper). These specially equipped mobile cranes were used to build the structures themselves and still do. When greater building height was needed, crawler cranes became the assist cranes and were used to assemble the stationary tower crane to the height possible. Moreover, these new magnificently designed tower cranes could raise (climb) themselves as well – to more than 1500 feet.

Any crane work requires caution. However, in congested urban areas, alongside busy streets and hundreds of feet in the air, it’s worst. Here, if things go wrong, members of the public are at risk. Not to put a price on human life, but killing an innocent member of society is much more expensive than killing an employee: the former is liability litigation, and the latter is statutory workers’ compensation.

ERECTING, JUMPING, AND DISMANTLING

In the years between 1989 and 2008 major tower crane accidents involving bystanders were broadcast through the country and still can be viewed on the internet. Investigating their causes produced increased awareness by designers and in erection methods. About 32% of the accidents occur when the crane is being erected, disassembled or extended, called “climbing or jumping.”

The climbing procedure will go as expected if the crew properly performs the method’s particulars! The “particulars” are that the section being inserted is centered between the sides of the “Climbing Frame” and the section slides up smoothly during the hydraulic jacking and does not bind, stall, or catch. To accomplish this centering a weight, (a tower section is used in this case, is moved in or out, causing the tower to lean one way or the other, centering itself to move freely. A crew member signals the operator when he visually sees the space between the two sections are “plumb.”

Rollers are mounted inside the Climbing Frame to reduce friction during “jacking,” aiding in the smooth movement between the sections. A fatal accident in New York of a tower crane that was being extended showed damaged and broken rollers which indicated misalignment of the sections had caused a binding. An attempt at re-alignment by rotating the crane caused the crane to fall some 200 feet into a busy street.

When the tower crane is being taken down (disassembling) the process of assembling is reversed. The tower is lowered by the means discussed above to the elevation required so that the erection (assist) crane can complete the dismantling. If the tower was erected completely using an assist crane, it would be dismantled in the same manner. In the recent Seattle accident, this was the process that was used.

ABUNDANT REGULATION – SMALL IMPROVEMENT

Cranes that are free-standing outside of the buildings next to city streets provide advantages. They’re able to extend themselves to greater heights (climb), and they work high over cities, but, they expose the public to falling hazards! How did industry struggle with the new exposures – painfully, I’m afraid! Five major tower crane accidents killing members of the public have dramatically affected national, state, and local safety regulations. My 2008 article “A Clamor to Regulate” goes into detail about what occurred and why it was unsuccessful.

REVIEW

As I see it, when caves for people weren’t convenient or available, humans started building structures to keep them dry, warm, and protected. These are the first of humankind’s objectives, (other than eating and reproduction) as far as shelters go! At first, people could stand on rocks or wood and hand up the materials to erect the walls and roof. Soon, these “hand” methods wouldn’t suffice; and the mechanical mechanisms entered into use.

Why higher and higher? Well, fort walls that were taller offered more protection from the enemy. And, elegant soaring vaulted cathedral arches just look lovelier and make one feel better. In modern times it is cost effective! But how high is high enough? The progress of the tower crane came from practical experience and job requirements – reacting to the work to be accomplished. Statistics (though sometimes misleading) indicate that operations and erection/disassembly and climbing the tower crane amount to about 75% of the tower crane accidents. Rigging and weather make up most of the remainder. Not many inspectors or operators fall off these cranes. Why? Well, as one that has climbed all over them, it’s my opinion that we know the risks, understand the safety equipment, do not need to be told to use it (kind of self-evident) and feel comfortable with heights!

OPERATION

A problem with the tower crane operation is, it’s always a long way between the operator and where the load is being attached. Also, most operators don’t know the load weight or how it is rigged; they depend on an overload device to stop the hoisting as well as a qualified rigger.

The ability of the operator to see the load (some cabs could be 600 feet away) and react to the unforeseen condition has always been “basic” to crane safety. The operator could stop or beep a horn, and is required to avoid carrying loads over people to prevent a possible accident – if he/she could see it coming! Some tower cranes now have remote controls that allow the operators to locate themselves closer to the “action” thus significantly improving visibility. However, most cranes don’t have remote controls, and to my knowledge, luffing tower cranes (boom type, versus a trolley for radius) are all cab operated. So, viewing the workplace is the signalperson’s duty via radio or hand signals.

Two tech devices are now in use on tower cranes to help the operator “see” the work area. These are video cameras and anti-collision devices. Both are useful, but not foolproof in all work locations and weather conditions. Thus, there is controversy among crane owners, hazard analyzers, and lawyers. Much of this controversy is, in my opinion, among the unknowing or vested interests – not to the improvement of hazard recognition for its own sake.

Next, the weight of the load is monitored on the cranes by load limiters. The crane is prevented from lifting more than 100% to 110% of the capacity. These crane capacities are based on the crane’s strength, not its tipping. The hoist motor stops hoisting when, on some cranes, the mast deflects the predetermined amount indicating an overload. Also on some cranes the trolley will stop when traveling out beyond capacity. It is critical to safe operations that these devices function properly and are tested monthly. If safeties don’t work correctly, then the old crane axiom “either the crane moves or the load moves” will prevail to horrifying outcomes.

To emphasize this point is a 2019 New York City regulation (fueled by accidents) mandating “crane event recorder” installation on all tower cranes working in the city. This device (labeled a Block Box) is to record any overload incident and status of limit switches. The problem I see here is, say, the overload switch fails and the “Black Box” records the malfunction, would that stop overloading? No. But, it would help in the “finger pointing” after an accident.

tower crane
Damage is seen at the site of a tower crane collapse at 91st Street and First Avenue in New York City on May 30, 2008, killing one person and damaging an apartment building on Manhattan’s upper east side. Photo © Shannon Stapleton|Reuters

ERECTING OR CLIMBING/DISMANTLING

Manufacturing changes in the crane design has lessened the “artistry” necessary to perform raising or taking down the crane successfully. It had been years since the papers were reporting a catastrophic tower crane accident in this country, until a recurrence in Seattle this year. Our society should respond to these devastating disasters since we all share the cost. The “big ones” in California, New York and, Florida brought on the significant OSHA Construction 1926.550 rewrite becoming 1926.1400 (17 pages to 213 pages.) The extensive studies conducted after the 2007-2009 tower crane accident “spell” exposed root problem areas. A task force formed in New York recommended needed areas of change – and industry responded. I’m sure the latest accident will be felt by the insurance companies who will pay out millions and feel the need to spread the cost to those they can! The most recent, Seattle, 2019, points to the disassembly crew errors in the tower lowering procedures.

Manufacturers were said to have made manuals unavailable or unclear forcing crews to resort to unsanctioned methods. Out of business or foreign producers increased the problems of providing proper assembly instructions to the workman. I have witnessed an improvement in the bulletin/manual information available to inspectors and specific hands-on training available to certifiers. Climbing Frame: each manufacture’s procedures and equipment used to extend or take down their towers is specific for the model. Think about what is going on when increasing or decreasing the crane’s height using a climbing frame. The tower is separated and unpinned, jacked up, and a section is inserted or removed. Then the top of the crane is lowered, and re-pinned. All this takes place when the operator is in the cab, maybe 500 feet in the air; the crane is fully functioning, leaving you to wonder, “What could go wrong?”

The newer designs offer better support, balance, and safety for workers than earlier models. Some designs connect directly to the turntable and the four corners.

WE HAVE TO ASK WHAT HAPPENED AND WHY

Accident records show that 70% (NYC statistic) of the people that caused the tower crane accidents, when hired, were held to a lower level of performance than that of a licensed hairdresser. Erection crews that were hired “presume” to be qualified based on hearsay, rather than documented specific training, experience, and licensing.

From experience, in Adult Skills Training Education, and evaluating material handling personnel, I find that some people should not be allowed to work unsupervised! Some lack the capacity to obtain adequate levels of performance. An employer’s due diligence will expose those unqualified for some job assignments.

It requires a healthy, well trained, motivated maintenance person unafraid of heights to erect or disassemble a tower crane. These people must be mature and willing to follow the manufacturer’s rules of use. These crew members perform their duties – unsupervised (journeymen), and it is the employer’s responsibility for the proper job assignment.

ANSWERS FOR ACCIDENTS

It looks like history is repeating itself! The latest Seattle accident investigation may go something like this: find out who told or allowed the crew to take out (photos show removal) all the tower section pins before they should have been detached, then sue them. Those that “dodged the bullet” will be delighted and go on about their business. Maybe some meaningless regulation change will take place, as in New York.

New regulations will have little effect on the “unsafe act.” To learn from this accident, we must find out why they took the pins out. Maybe:

  1. Fatigued, easier to remove all the pins and get to the ground, so you’re not hanging on the tower for hours, no “man basket” to suspend crew.
  2. Saw someone else do this on another job and it worked out okay, observing an unsafe method that did not cause an incident and tried to emulate – a big OJT problem.
  3. This crane tower has 18" section sleeves and should hold without pins when being dismantled compared with towers that have only a 2" centering lug and bolts, like the last one we worked on.
  4. Was not trained, didn’t know better.
  5. Other reasons?

Once the “why” of it is learned, proper corrective action can take place. Humans are the cause of “unsafe acts.” Safety can only be improved by properly trained and motivated people.

 

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