Toolbox Topic: Overhead Crane and Hoist Safety
Overhead crane and hoist safety can be the difference between life and death. In this episode, we will discuss ways you can stay safe when working with overhead cranes and hoists.
Definitions of Overhead Crane
According to OSHA 1910.179(a)(8), Overhead crane means a crane with a movable bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure.
In other words, Overhead cranes move loads side to side, backward, and forward over a rectangular area.
History of Lifting Devices
Starting in some of the earliest civilizations, man created machines to lift objects to heights never imagined. From an engineering perspective, these devices were impressive. The only significant difference today is our ability to power these machines.
The Egyptians used the principle of a seesaw or teeter-totter to develop simple lifting devices such as inclined planes and levers. Clearly, moving something up a ramp rather than lifting it straight up requires less force but takes more time.
There are somewhere around 140 Egyptian pyramids. Most of the stones that make up the pyramids weigh 2 to 3 tons. Some of these stones can weigh up to 50 tons or more. The pyramids can reach 147 meters or nearly 500 ft.
Although the Egyptian’s methods were advantageous, they required massive manpower. Some historians estimate it took between 20,000 and 50,000 men over several decades to complete some Pyramids. Similar structures are built today in just a few years using powered cranes and a small workforce.
Cranes began appearing in Greece around the 5th century BC. They were simple machines that used a rope passed over a pulley. Early on, the single pulley was used for drawing well water. A single pulley changes the direction of the pull but offers no real mechanical advantage. Pulling down on a rope is always easier than pulling up. Later, in the 4th century BC, the compound pulley was developed, combining single pulleys into a block. The mechanical advantage is equal to the number of pulleys used. So, a crane with five pulleys allows you to lift five times more than you otherwise could. The disadvantage is that the rope must be pulled over five times the distance.
Winches and capstans
Another significant improvement was the introduction of the capstan and the winch. The only difference between the capstan and the winch is that the former has a verticle axle, and the latter has a horizontal one. Both devices substitute for pulling the rope by using handspikes or levers inserted into slots on a drum that moves in a circular rotation. They were invented around the same time as the compound pulley.
When you combine the capstan or winch with a compound pulley, it creates a powerful lifting machine. A single man exerting a force of 110 lbs. can lift 3300 lbs. To perform a similar task, the Egyptians would have required 30 to 60 men.
Around 230 BC, treadwheels started appearing and were used until the latter half of the 19th century. Treadwheels generate power by walking within the wheel, which is much greater than just using your arm and shoulder to turn a winch or capstan. Typically, these devices have a diameter of 4 or 5 meters. Because of the wheel’s larger radius, they have a greater mechanical advantage than winches or capstans. Depending on the size, a treadwheel can have a mechanical advantage of 14 to 1.
Similar to overhead cranes found in many shops today, the first horizontal crane was created in 1666 by Frenchman Claude Perrault. A trolley could be moved along the entire length of the jib by two ropes that were wound and unwound via a spindle attached to the trolley. In fact, one of the early uses was for building carriages and stagecoaches. The overhead crane could set the cab on its axle and provide easy access for installing the wheels.
At first, the speed of lifting machines was extremely slow, while the amount of manpower required to operate them remained high. However, later in the 19th century, before steam power became available, human-powered devices became so sophisticated that a single person could lift 15 tons using one hand.
Crane safety mechanisms were introduced late in the 18th century. These features would prevent falling loads and sudden reverse rotation of the treadwheel or capstan.
Cranes have continued to develop, and today the most common tower crane can lift anywhere between 12 and 20 tons. The average overhead crane has a capacity range from 1 to 16 tons. These cranes are widely used in factories, warehouses, and stockyards.
Crane Safety Statistics
According to an extensive 10-year study, there were 249 industrial overhead crane incidents. The study revealed the following:
- 37% crushed by the Load
- 27% dropped loads, with the root cause being poor rigging
- 12% of the victims fell from heights of 8 ft. to 100 ft. or more
- 11% were crushing injuries -almost all of these resulted in a fatality
- 6% were due to either improper Lock Out Tag or failure to Lock out tag out The result was 838 OSHA violations and 2.3 million dollars in fines. Half of these incidents ended in injury, and the other half were fatalities.
Overhead Crane Safety Tips
Safety Tip #1 – PPE
Crane operators, riggers, and any other employees who work in areas where overhead cranes operate should wear the appropriate PPE, including hard hats, safety glasses, gloves, and steel-toed boots. As always, observe your company-specific requirements for your location.
Safety Tip #2 – Frequent Visual Inspections
Perform a crane inspection at the beginning of every shift or whatever frequency your company currently mandates. Document all crane inspections. If you are using the crane after it has been inspected, check and ensure the inspection is complete. Visually inspect the crane and surrounding area:
- Check for good housekeeping, look for leaks or other tripping hazards
- Inspect the wire rope for damage
- Inspect the drum for proper rope alignment
- Inspect the block and hook
- Inspect the bumpers
- Look for deformed, distorted cracked, or corroded parts
If issues are discovered during inspection, do not operate the crane and report immediately
Safety Tip #3 Operational Test
A Basic Operational Test should include:
- Operate the crane in each direction and listen for any unusual noises or jerky movements
- Check the control station and make sure all the buttons are labeled- make sure it functions correctly and it doesn’t stick
- Raise and lower the hook
- Check the upper hoist limit switch- slowly raise the block to trip the limit switch
- Lower the hoist block to activate the lower limit switch if the crane is so equipped -if not, stop the block before it contacts the floor
- The hook must have a safety latch that closes
- A warning tag should be located on the control station or lower hook block with some reminders about many of the checks we just covered
Safety Tip #4 General Safety
- Be sure to ask your employer if there are any special certifications needed before operating a specific piece of equipment
- Stay alert and pay attention to the warning signal from overhead hoisting equipment
- Never carry a load over another worker. Never stand or walk under a load
- Never operate an unsafe crane
- Never allow unauthorized persons to operate the crane or give hand signals
- Lock out equipment when doing any repair work
- Never exceed the limits of the equipment
- If the lift appears to become unstable or unsafe, stop immediately
- Do not operate any overhead crane tagged out or marked as ‘do not operate’
- If it is necessary to leave the controls unattended lower the load first As we discussed in the worker fatigue episode, ensure you are alert and have had sufficient rest before operating equipment
Safety Tip #5 Operators, Riggers, and Signal Persons
Hoist operators and riggers should be trained in standard crane operation hand signals. This is especially important for situations when voice communication could be interrupted
Operators and riggers must know the load ratings before attempting the lift
Verify that the load is not heavier than the maximum load capacity
Operators and riggers should not engage in any behavior that could divert their attention
The operator and signal person must stay in communication at all times