Photo: Giant Liebherr LR crawler crane, used for loading wind turbine components at the Belfast Harbour, Northern Ireland, UK. Photo © Douglas Lander | Alamy Stock Photo
Gigantic Cranes – Are We Getting Too Big to be Safe?
Toolmakers have transformed two simple machines into the crane. Due to modern technology, they have become monsters. Are they too big to safely control? Only accidents will tell!
by Dennis J. O’Rourke, CSP
NOTE: more photos and diagrams in the Gigantic Cranes article in the June 2020 issue of Wire Rope News & Sling Technology
Crane Safety depends on basics:
- Manufacturers build and owners assemble cranes correctly,
- depending on environment and use, cranes are maintained correctly,
- cranes are operated correctly.
This article makes three primary points. Accidents have changed standards. The improvements in hoist design has allowed the building of massive cranes. And, largest has not eliminated hazards.
To discuss the complex problem of raising a load against gravity, it’s necessary to gain an understanding of the operational purposes. We have labeled the “tool” that evolved from the 17th-century lifting devices as a crane. One of the crane’s purpose is to hoist a load, hold it aloft, and regulate lowering speeds. A second purpose of the crane is to move the suspended weight horizontally by booming up/down or rotating on its base. To accomplish the myriads of possible work requirements, the Tool has mutated into a monster. Fig. 1. Its proper use requires superior skill to manufacture, erect, maintain, and control.
How did the toolmakers transform two simple machines, the lever and the block and tackle into the modern crane? From hoisting a one-haft-ton cargo box aboard 17th-century ships to lifting a thousand-ton object at a 105-foot radius to 150 feet in the air? As I described it, taking one uncertain step after another. We could fill all the pages in this magazine with spectacular accident photos. As I write this, a 5000 metric ton ship crane fell in Europe when being tested. The hook failed, which should interest readers.
Driving this “progress” is humankind’s desires and the toolmaker’s talent to satisfy the market’s “pull” for bigger and faster tools. Plus, a customer ready to pay for them. Have the limits of improving these simple machines been reached? Will the use of CAD design, exotic materials, hydraulic controls, electronic assemble monitors, computer operator overrides, programed auto-maintenance, 3D generated lift plans, and video recorded coordinating practice-run reached maximum advancement? Will humankind’s lust exceed the toolmaker’s ability to provide what the human can control; only expensive accidents will tell.
The past shows us that the fundamental laws of the natural world will halt a mutant progress. I did not attend the abbreviated ConExpo in Las Vegas this year. Friends that did say they’re glad they retired from the business, ha. These experienced people’s opinions are that cranes have evolved beyond the “respect” needed for the operators to control them!
In an instance, the operators decide if they will respond to a hoist signal. The training objective is to improve the excellence of that decision process. The various methods of achieving this are qualifying candidates, testing, practice-runs, and work skill.
Sight, sound, and feel are the instincts the operator uses to anticipate the reaction of their crane when moving an object! Safety requires people to react correctly the moment the strain of a lifted load is sensed. No one, whoever hoisted an object, didn’t hesitate to sense if the crane is “getting lite” when the weight first becomes free of the earth.
Sheer size compromises the operator’s abilities. And now, much of a crane’s capacity is based on breaking, not tipping, so “feel” is irrelevant. Ideally, if the operator can see where the burden is picked-up at and where it is to be landed are desired. If both locations are not visual, the operation is deemed riskier.
HOW WINCHES OPERATE
Improving crane controls and winch development enhanced safety. Older friction cranes required eye, hand, and foot coordination to be perfect each lift to prevent dropped cargo, ground workers beware (statistics show people around cranes are killed on a ratio of 10 to 1). A crane control diagram of the 1940-1960s era, Fig. 2, was a training view graph I drew and used in the ’70s. It shows the complicated arrangement for operating this 25-ton port crane.
A task, let’s say, to make a change from the main to the whip hoist, is as follows.
- Set the drum pawl (dog) on the main hoist.
- Slowly release the foot brake pedal, main, till the drum stops rotating downward and is held in place by the pawl.
- Set the foot brake on the main, push down hard and pivot foot to engage floorboard ratchet to keep/set brake.
- Disengage clutch lever.
- Engage clutch lever on whip hoist.
- Release whip foot brake pedal and hold foot pressure.
- Slowly hoist up, via motor control, right hand, and disengage whip pawl by pulling pawl lever back with the left hand, and latch in place.
- Release whip foot brake pedal, the whip will now be coupled to the drive motor.
Unfortunately, some loads and booms were dropped during these transfers, so learn well.
CONTINUOUS DRIVE WINCHES
Called friction cranes, manufactured in the 1960s to the ’90s, did away with the hazardous requirement of switching the winch connection from the power source (in most cases). One master clutch or torque convertor coupled the engine/motor to all the winch drive shafts that rotated the internal expanding friction clutches.
The operator would pull back a lever and engage a rotating friction clutch, say main hoist, via the main hoist controller, release the foot brake, and the main block raises at engine RPM speed. By placing the control in neutral releases the friction and the block free falls, under the foot-brake influence only. Fig. 3. Loads were dropped.
Next, the hoist winch on friction cranes began to have power-down features added for safety, also providing precision load lowering when connected to torque converters. The two-position control was devised. Pull back, friction #1 rotating counter-clockwise engages the drum, release foot brake, the block goes up. Push forward, friction #1 releases and friction #2 turning clockwise engages, (or vice versa), and the block is power down at engine RPM, stall the engine due to low throttle with a manual clutch, and the load would fall. Control in the center, free fall, required holding a load with the foot brake. Weights have sometimes dropped due to improper brake or friction condition/adjustment, or operator error. Fig. 4
Booms falling were devastating, standards were changed to require a control lever having three-position. In the center, an automatic brake would set holding the drum from rotating. No foot-operated pedal was needed. This feature improved safety.
The methods mechanically for reversing the rotation of a drum are by; a reversing chain (American, Fig. 5) cross-over shaft (Link-Belt), the planetary drive (P&H), or beveled gears and apposing clutches. All mechanical systems work well. However, they add components that require proper repair and adjust for safety. Loads have dropper due to poor maintenance.
The next and final improvements for lattice boom cranes, now called conventional cranes (they travel, boom, rotate, and hoist), are the hydraulic winches and controls produced today. The three-position controls with free-fall switch and foot brake function for light loads (if equipped.) Now, the operator chooses a lever to activate the winch. Say, the main-hoist, pushes forward, and the block is powered down, speed dictated by the throw of the control-lever, center position auto-sets the brake, and pull back is power up. Wow, easy, no more problems. Fig. 6.
If (knew this was coming), the electronic wiring, pressure switches, movement sensors, and hydraulic dampers that take their orders of selection/position from the operator’s lever—and the winch performs the desired response—will work like magic. Fig. 7
The friction winch can be inspected outwardly for breakage, wear, adjustments, and contamination, Fig. 4. The hydraulic winch is sealed figure # 7. What is usually done for these sealed winches is an exterior look-see and a functional check of pressures. Manufactures require a periodic disassembly to expose inside components for inspection of wear.
Here’s the point, the development of the modern hydraulic winch with its electronic speed ramping and it’s hydraulic dampening has helped remove some of the shock loading and excessive operating speeds, improving safety. Also, it has reinforced the arrogance of tool builders and customers, thinking that the sky is the limit.
The crane in figure # 8 folds out like a “Swiss” army knife. Some cranes appear to be an experiment with a giant erector set. How big should cranes become? All of these erection manipulations and connecting subjects the crane to structural damage, and boy that happens! We must be on-site to witness crane erection.
A crane is a Class 1 Lever with two tipping fulcrums. Fig. 9 is a training viewgraph from the ’70s I still use. It shows the fundaments of the design and directions of the forces on cranes.
The machinery deck is the central support like the board of a kid’s teeter-totter, more weight on one end, and the board teeters on the fulcrum, remove the weight, and the board totters back to level. Crane’s have two fulcrums, the front, and back of the turntable, providing a range of stability to keep the crane level as a load moves.
This diagram is of a connected, mechanical assembly illustrates how the “System” center-of-gravity (C.G.) or balance point can be calculated by knowing the weight and C.G. of the individual major components. By increasing a load (red arrow), the connected system C.G. will move toward the forward tipping fulcrum. Too much loading overturns the crane.
Second, to keep the machine deck level when the load is moving away by booming down, via the boom’s luffing ropes (increasing the operating radius), the weight must be reduced to maintain level, the purpose of a capacity chart. Cranes are “variable” capacity machines.
The American Sky-Horse first available in 1970 started the “we can build them bigger” trend that continues today. Comparing the #9 diagram to the Sky-Horse, figure 10, and using a little ingenuity, we have a crane, 65-ton lift at a 150-foot radius. The Sky-Horse extended the counterweight distance from the machine deck; greater leverage is gained to lift more massive loads—back further, more capacity, till the strength of the teeter-totter is the limiting factor and breaks, and they have.
What drove the demand for this phase of the tool’s development is modular construction methods. It is much cheaper to build it on the ground and set it in place with a crane. Some of the four-story hotels around Walt Disney World were built during the ’70s using these methods with smaller modules. Today cranes lift forty-ton apartment modules 300 feet and set them in buildings. The maritime and petroleum industries also increased this market.
An opportunity for designers occurred when the modern hydraulic winch was incorporated into the heavy lift class of the conventional cranes. The enormous machines of today would not have been possible without the improved winches and controls discussed herein.
So, referring to Fig. 9, we see that the winch draw works must be clustered on the machinery deck to mechanical link to the engine. Now, these engines drive pumps (Fig. 7). Released from the direct-connection requirement, designers can locate the hydraulic winch for structural advantage, flexibility, conveniently place the winches, and attach the hydraulic lines. “Giganticus” is born, Fig. 1, nothing can hold us back now!
ARE CRANES SAFER?
BUT PEOPLE ARE THE SAME!
Modern-day cranes can do all that the toolmakers say they can, but only under perfect conditions, properly maintain, certified erected, and the people act like programmed robots. What are the chances of that? Cranes built thirty years ago or so were a little more forgiving!
How a four-hundred-ton full-hydraulic truck cranes can rollover when they contact a road shoulder, they aren’t a 400-ton crane on their side; rollovers are happening more these days. With new hydrostatic drives and automatic transmissions, they can zip down the road. Driving cranes fast, hydraulics reservoirs, tires, and exhaust heat-up, fires start and are on the increase as reported to insurance carriers.
The statistics are misleading when identifying accident causes, only trend, somewhat helpful. Why, two main reasons, they don’t use a common denominator for comparison, like types of cranes, job activities, etc., just raw numbers. And, if the numbers of accidents don’t reflect your work environment or exposure, they don’t apply.
Generic safety training does little to change habits or identify hazards in the work area. Training must focus on dedicated crews, the job, and specific cranes. I call it crew-job-crane (CJC) evaluation. Sounds so simple you would think employers would do it, here’s why they don’t, cost and operator turnover. Erecting these monsters takes experience, not OJT. Fig.11
In 1982 OSHA, I review all crane accidents recorded between 1971 and 1981, their first ten years in services. The results from this study revealed the bulk of the accidents were improper crane set-up and overloading, 75%. Other significant categories were wire rope failures and death by electrocution. Back then, data gathering methods were weak. After the study, procedures changed, and report content improved to yield better data. However, the data must be evaluated correctly.
The lasts decades show stunning erection/assembly accident of heavy lift cranes, structural failures, erected cranes on-site, and tower cranes. Also, fires and rollovers of large hydraulic truck cranes. What type of accident exposure you have will depend on your cranes and operations—never around power lines—no electrocutions! To be safe, you need a C-J-C evaluation of your work and enforce your rules.
WHO ERECTS AND MAINTAINS GIGANTIC TOOLS?
One more thing, dear to my heart, is the maintenance workers putting all these big cranes together and keeping them running—their safety. Little thought of them when they are hurt, oh, that’s workers’ comp, no litigation! They should have known better than to do that. They just made a mistake, is said. About fifty years ago, when I was a Safety Engineer for a major casual insurance company, I read a disturbing statistic in “Accidents Facts,” a publication for the insurance industry, discussing deaths on the job.
Expressed in this publication, if you were a maintenance worker on heavy equipment, elevators, or electrical devices, you had the highest chance of being killed on the job than any other classification of the non-emergency American worker. Seems reasonable, seeing that the “big three” in death causation are falling, caught between moving equipment, and electrocution.
In a Repair Manual by Caterpillar Tractor Corporation, I read the following, posted on the inside cover. “You can reduce injures to your valued maintenance worker by 80%. They knew workers were going to read this, (buttering them-up) by following one safety rule—never inspect, lubricate, or adjust moving equipment.
I thought what about the other 20%? In those situations, the people must—inspect, service, or adjust “moving” equipment? Advice like this reminds me of a joke I told from those days, “Their safety program depends on loud horns, good breaks, and fleet-footed pedestrians.” Not so funny now that I am older. The fact is, there are hazards out there.
The higher we go to work, the more difficult it becomes. Ever think about fatigue, as in getting tired of climbing? Oh, no, go on, don’t wait for the walkways, there for the other people, besides, someone needs to install them—that’s you!
Here’s the problem. When people are working, they are focused on what they are doing—not on where they are located. They “assume” their platform is substantial, the guard rails are secure, the man basket is correctly secured to the crane, the power is off, pins are seated, hand signals are understood, and I’m sure I missed your favorite. The real world, the higher and bigger we go, the harder it is for us to maintenance the cranes. We must wait until the dawning of the flying erection robots.
The next crane catastrophes will usher in a few more regulations that are meaningless for improving safety. The formulation of new regulations is not to reduce risk but to identify blame. What is needed, an experienced, dedicated crew that won’t cut corners and near-perfect weather conditions.
I started writing this article talking about simple machines, lever and the block & tackle, and how they became cranes. The tackle part of this machine is the wire rope. Rope wearing out and breaking is an old problem that is still bringing down today’s monster cranes. Only now, it is much harder to locate worn rope in 1800 feet of reeving tackle and looking for it 200 feet in the air.
What will stop this mutant Tool’s Gigantism—not newer winches or deaths? Money, when the cost of the tool is higher than other construction methods, the market will shed this bug faster than a bad habit. Toolmakers, take note of buildings constructed with 3D printing technology and aircraft.
ABOUT THE AUTHOR
DENNIS J. O’ROURKE, CSP, is the Director of National Crane Services, Inc. He has over sixty years’ experience in the industrial, maritime, and construction fields working with heavy equipment and material handling devices. As a safety engineer, Mr. O’Rourke has developed and/or presented hundreds of safety-training programs for all representative elements of government and industry. (firstname.lastname@example.org)