MRO Today - Safe cranes and hoists are no accident

Safe cranes and hoists are no accident

by Dan Anderson

The heart-stopping ba-BAANNGGG! brought workers running from all corners of the west wing of the building. They found Jeremy, a new-hire, in a jumble of massive steel frames, his lower leg pinned between two 6 foot x 6 foot steel box beams.

The shop foreman grabbed the pendant control box for the overhead crane from Jeremys hand, quickly reset the lifting chains and eased the frame up so other workers could pull the white-faced young man to safety.

Jeremy was hauled to an emergency room, where he was diagnosed with torn ankle ligaments and a broken bone in his foot. Relatively minor injuries, considering what could have happened, but still a Workers Comp case, with added expenses and lost time for the shop.

Back at the shop, a veteran worker began untangling the wreckage, under orders from the foreman to, "figure out what happened."

After a half-hour, he reported to the foremans office. "It was an accident waiting to happen," he told his boss. "He had rigged the frame he was lifting off-balance. To make up for it being off-balance, he stood inside the frame, lifting one side while he moved it sideways with the crane. Besides that, he had tied knots in the load chains to shorten them up, and was using just the tip of one load hook to lift one side of the frame.

"Boss," he drawled, "it was just a matter of time before he hurt himself or somebody else. That crane is no smarter than the man operating it, and it was a really dumb crane today."

Unfortunately, to err is human
"If you trace everything back to the root cause, human error is the most common cause of (hoist and crane) accidents," says Chris Hess, manager of engineering and quality for Harrington Hoists.

"They try to lift too much, or dont have the load balanced, or lift it over themselves or other people and accidents happen," says Hess. "Its not enough to know how to make a hoist go up and down by pushing the buttons; you have to know how to operate it properly."

Proper maintenance avoids overloads and overlooks
Mechanical failures of hoists and cranes have two primary causes: overloads and overlooks. Both are caused by operator error.

Overloads are caused by operators attempting to lift loads that exceed the capacity of their crane or hoists. Cranes and hoists should have their maximum capacity painted or decaled in plain view. Operators have a responsibility to know the weight of any load to avoid overloading their equipment.

A frequent cause of overloading equipment is mismatched components. If a component is replaced with a smaller component during maintenance or repairs, the lifting capacity of the entire unit is diminished.

"Substitution (of parts) can be a real problem," says Curt Jabben of The Crosby Group. "Especially on older equipment. For example, someone uses a common, Grade 5 bolt in a shackle instead of a hardened steel pin like the shackle had when it left the factory. If the bolt breaks, theyll say it was a mechanical failure, when it was really human error."

Overlooks are the other human error that causes crane and hoist failures. Chains, cables, hooks and other mechanical components rarely fail without giving subtle advance warnings. Deformed lift hooks, stretched chains and other signs of wear or stress are "red flag" danger signs that need immediate attention.

Lift hooks should be replaced if they are deformed by more than five percent. Wire rope sheaves are risky if there are cracks in the spokes or webbing. Wire ropes should be replaced if wires are frayed or kinked. Chains should be replaced if any links are stretched, cracked or deformed.

Adjustment of safety features is another "overlook" that can cause accidents. "On electric hoists, there are features that should be maintained and kept properly adjusted," says Harrington Hoists Chris Hess. "Load brakes, slip clutches, load limiter switches and travel-limit switches are designed to help prevent load slippage, overloading and over-travel. These features on a crane or hoist should be checked on a regular basis to make sure they can do their job."

Operator training is the key to safe and trouble-free crane and hoist operation. Even if operators dont do the equipment maintenance, they must make sure it is maintained and must call worn or damaged components to the attention of maintenance workers.

Safe operators a MUST
Safe operation starts with careful selection of operators. Ideally, a crane or hoist operator should have good hand-eye coordination, as well as good depth perception and spatial orientation. Maturity, willingness to perform maintenance and good safety habits are also attributes to look for in those who will frequently operate cranes and hoists.

Operators must be trained in the operation of the crane or hoist they will be using. They should know the maximum lift capacity of the unit and be trained in how to inspect and maintain it. Training should emphasize the safety and overload features of the equipment they will be using, including slip clutches, top hook load limit devices, braking mechanisms and wear gauges such as "quick check" marks on lift hooks and chains.

Cranes and hoists used in assembly lines where operators frequently lift similar loads should have charts showing balanced lift points and safe rigging techniques.

If operators will be lifting and moving a variety of loads, training should emphasize safe rigging practices. Operators should know the total weight of each load and learn to estimate the center of gravity before attempting to move a load.

"A lot of times, people dont take time to figure the pick points and center of gravity before using hoists," says Curt Jabben, assistant marketing manager with The Crosby Group. "They just hook on, start lifting and then try to figure how to stabilize the load if its off-balance. That can be dangerous."

Watch for side-pull
Loads should always be lifted vertically. Side-pulling a load puts unnecessary stress on a crane and its hoist and risks sudden, uncontrolled swings when the load becomes suspended. Loads should never be lifted over personnel, and lifted only high enough to clear the floor or obstacles.

End-stops on crane girders or beams should not be used to stop horizontal movement of load-bearing trolleys. While end-stops are usually sturdy enough to stop loaded trolleys, the sudden, jolting stop can stress every component of a crane. On hoists powered by electric motors, operators should avoid "jogging" the motor to start or stop loads or to make fine adjustments. Some jogging is unavoidable, but quickly bumping a control button off and on causes excessive amperage loads to the motor, which can cause heat and eventual failure.

Get help if you need it
Finally, when lifting large loads or using cranes where the operator cannot always see the load, "spotters" should help direct the cranes operator.

In noisy environments, use prearranged hand signals. Construction workers use universal hand signals, but many industrial workers use a mish-mash of Marcel Marceau hand gestures that can be confusing, if not dangerous. Agree on hand signals for "up," "down," "faster," "slower" and "stop" before beginning any lift utilizing more than one worker.

This article appeared in the February/March 1998 issue of MRO Today magazine. Copyright, 1998.