Knowing how cranes should be used, and how they should not be used, is critical to crane safety. Overload, side pull, limit switches, secondary braking devices, using the reverse direction for speed control, and daily inspections are surrounded by myth and mystery in the workplace. Sometimes it's a easy as pie but sometimes.. The operator just gets a little cocky!
Overload
Misconception. The crane will handle any weight I throw at it! The manufacturer wouldn't make a crane that could shift things!
Fact. This is the single most dangerous misconception about overhead cranes. Although some parts of an overhead crane are designed with a built-in safety factor, this is not true of the whole crane system. Furthermore, the crane is attached to a 'building' that does not have these same safety factors. Picture an overloaded crane sitting on the floor amid a collapsed building because the crane's safety factors were greater than the building's.
The crane and building probably were supplied by the lowest bidder. Do you really want to bet your life that the low-priced bidder put in extra capacity that wasn't asked for? Because I know I wouldn't! Do you know exactly what 30 tons is when you see it? I know for sure I don't...
Fact. This is the single most dangerous misconception about overhead cranes. Although some parts of an overhead crane are designed with a built-in safety factor, this is not true of the whole crane system. Furthermore, the crane is attached to a 'building' that does not have these same safety factors. Picture an overloaded crane sitting on the floor amid a collapsed building because the crane's safety factors were greater than the building's.
The crane and building probably were supplied by the lowest bidder. Do you really want to bet your life that the low-priced bidder put in extra capacity that wasn't asked for? Because I know I wouldn't! Do you know exactly what 30 tons is when you see it? I know for sure I don't...
Side Pull
Misconception. As long as the hoist has enough rope, I can pull a small piece of steel out of the adjoining bay without a problem. After all, the piece I'm picking up is well below capacity.
Fact. This is one of the most common mistakes made with overhead cranes. Hoists and cranes are designed to lift straight up and lower straight down only.
Side pull causes a number of dangerous conditions. First, the wire rope often comes out of its grooves and "scrubs" against the remaining rope or drum, resulting in damaged rope. Sometimes the rope actually jumps the drum and tangles itself around the shaft, resulting in stress to the rope. Too much stress and 'SNAP!' there's now that danger too!
Just stick to what the crane was designed to do! Lift UP and DOWN!
Fact. This is one of the most common mistakes made with overhead cranes. Hoists and cranes are designed to lift straight up and lower straight down only.
Side pull causes a number of dangerous conditions. First, the wire rope often comes out of its grooves and "scrubs" against the remaining rope or drum, resulting in damaged rope. Sometimes the rope actually jumps the drum and tangles itself around the shaft, resulting in stress to the rope. Too much stress and 'SNAP!' there's now that danger too!
Just stick to what the crane was designed to do! Lift UP and DOWN!
Upper Limit Switch
Misconception. Im lifting a huge load! I need all the height I can get? So I should lift until I hit the 'Upper Switch Limit'?
Fact. Again, this seems like common sense, but it's dead wrong. The upper limit switch in a hoist is designed to prevent the hook assembly from colliding with the drum. It is a safety device!If the ultimate upper limit switch fails, the hook block and the drum will collide and the wire rope probably will fail, dropping the load. Probably crushing anyone below!
If you need an operational upper limit switch, install a second switch that is wired in a fail-safe mode. That way, if the operational limit switch fails and the ultimate upper limit is struck, the hoist still will turn off. Failure of the ultimate limit switch shuts down the hoist in the full up position, telling the operator to get help. If you don't wire it in this manner, you won't be able to tell when the first switch has failed until they both fail and the crane drops the load.
Fact. Again, this seems like common sense, but it's dead wrong. The upper limit switch in a hoist is designed to prevent the hook assembly from colliding with the drum. It is a safety device!If the ultimate upper limit switch fails, the hook block and the drum will collide and the wire rope probably will fail, dropping the load. Probably crushing anyone below!
If you need an operational upper limit switch, install a second switch that is wired in a fail-safe mode. That way, if the operational limit switch fails and the ultimate upper limit is struck, the hoist still will turn off. Failure of the ultimate limit switch shuts down the hoist in the full up position, telling the operator to get help. If you don't wire it in this manner, you won't be able to tell when the first switch has failed until they both fail and the crane drops the load.
Daily Inspections
Misconception. The crane worked yesterday, so I can assume it will work today.
Fact. Daily inspection is the simplest but most overlooked rule of crane operation. This inspection doesn't require a maintenance person, just a common sense check list. It should take one operator about one minute at the beginning of each shift:
Look. Take a quick survey of the area. Does the crane look to be in operable condition? Have any parts fallen to the floor? Is anything hanging? Are there any signs of collisions or damage?
Listen. Start running up the hoist. Do you hear any unusual sounds? Does the hook stop when it hits the upper limit switch or when it is lowered to the ground? (Not all hoists have lower limit switches, so check with a supervisor before performing this test.) Does the trolley and bridge movement sound right? Does the hoist appear to be working in all directions, and are the buttons' directions consistent with the movement? (Remember, if the power phases have been reversed, the directions buttons will be wrong, and all safety circuits will be disabled.) Are the end stops in place and functioning?
Document. On the daily inspection sheet, check off that the crane looks and sounds operational and that it performed normally. Afterwards write your initials/signature!
The misconceptions discussed here probably represent a small fraction of the issues involved with crane safety, but they comprise the overwhelming majority of crane accidents and breakdowns. Make sure you and those around you understand these six topics, and chances are you'll have a safe and productive day.
Fact. Daily inspection is the simplest but most overlooked rule of crane operation. This inspection doesn't require a maintenance person, just a common sense check list. It should take one operator about one minute at the beginning of each shift:
Look. Take a quick survey of the area. Does the crane look to be in operable condition? Have any parts fallen to the floor? Is anything hanging? Are there any signs of collisions or damage?
Listen. Start running up the hoist. Do you hear any unusual sounds? Does the hook stop when it hits the upper limit switch or when it is lowered to the ground? (Not all hoists have lower limit switches, so check with a supervisor before performing this test.) Does the trolley and bridge movement sound right? Does the hoist appear to be working in all directions, and are the buttons' directions consistent with the movement? (Remember, if the power phases have been reversed, the directions buttons will be wrong, and all safety circuits will be disabled.) Are the end stops in place and functioning?
Document. On the daily inspection sheet, check off that the crane looks and sounds operational and that it performed normally. Afterwards write your initials/signature!
The misconceptions discussed here probably represent a small fraction of the issues involved with crane safety, but they comprise the overwhelming majority of crane accidents and breakdowns. Make sure you and those around you understand these six topics, and chances are you'll have a safe and productive day.
And whatever you do! DON'T DO THIS!!