What is Crane Blocking?
Cranes are very powerful devices. Using hydraulic lifts, they are able to hoist extremely heavy objects, and place them in specific locations. However, since cranes can lift their own weight (if not more), there is a looming fear that they will tip over or lose control of the load. A strong foundation is key to maintaining the integrity of the crane’s lifting potential. This balancing act involves a very specific and calculated procedure, known as "blocking.”
Blocking is the act of distributing weights to ensure the crane’s stability when lifting extremely heavy loads. There are distinct calculations for establishing parameters, procedures for aiding the process, and dangers associated with blocking improperly.
Crane Blocking Calculations
In order to block properly, knowing the specs of your crane is essential. Given these specs, there are two rules for establishing the parameters of blocking. These are the Rule of Three and the Rule of Five:
Rule of Three: Multiply the square footage of the crane’s floats by three. For instance, if the crane’s floats were 4x4 feet (16 square feet), you would multiply by three to get 48 square feet.
Rule of Five: Divide the crane’s maximum lifting capacity by five. For instance, if the crane can handle 20 tons, then you need 4 square feet of blocking.
Rules of Proper Crane Blocking
The following rules will help you maintain proper crane blocking and practices.
Make sure the base is level: Always ensure that the ground beneath the crane is even, as uneven ground can cause a weight differential and jeopardize control of the load.
Check for inconsistencies with the blocking: Search for cracks or bends in the blocking, or any sort of displacement or movement from its initial location.
Don’t over-block: Often times, blocking stacks are made to increase the stability of the blocking. This is not a problem, so long as the stack’s height is not greater than twice the width of the blocking. Otherwise, it distorts the center of gravity, and causes balance issues.
Make sure the outriggers have a solid level surface: If there is any debris underneath the outriggers, or anything else that inhibits a solid, level surface with the ground, you must remedy the situation. Outriggers allow the crane to stand firm.
Paying Attention to Ground Surface:
The lifting potential of the crane is a product of the ground beneath the crane. The total pounds per square inch of load bearing potential depend on how well the ground can support the crane. Asphalt and silt soil will yield a low psi, often ranging from thirty to forty psi, whereas a more robust material, like concrete, can establish a psi of nearly one thousand.
Overall Safety Procedures:
In addition to the blocking rules listed above, there are certain rules that should always be maintained, even if blocking is done correctly.
●When operating a crane, ensure that workers in the proximity are absolutely necessary. If the integrity of the blocking fails, it is best to have as few people around as possible.
●For workers who are nearby, ensure that you do not lift any materials over the worker, and that the worker is not under the load for any reason. This is how a vast majority of workplace accidents occur.
●Ensure that there is always a supervisor on the ground to guide proper crane operations.