In the last post, we discussed the significance of a checklist in preparing a crane or hoist for use. Though this post will be taking a different turn regarding safety, the preliminary checklist that was previously discussed plays a momentous role leading up to the current topic. The primary reason that we encourage the employment of checklists into your daily routine as a crane operator is to prevent accidents such as tipping, which can result in severe, and perhaps unforeseen, consequences. Crane tipping is the most common problem that portable mobile cranes and gantries face, but it’s one of the easier crises to avert. As long as manufacturer ratings, instructions, and checklist are all followed, the likeliness that tipping accidents will occur is fairly low.
Just like when any other object tips over, the weight of the load on one end of the object is too great. The balance between both sides is uneven, which leads to leaning and potentially falling over. Just like a human, a crane is more likely to tip over when it is in action, specifically if it’s carrying too heavy of a load. A load chart is provided by manufacturers and is to be used by an operator to find out the maximum weight that the crane can support. This is dependent on the length of the boom and the angle at which it extends. Tipping issues arise when the operator disregards the load chart or is given an incorrect reading of the load’s weight. One statistic reports that a crane tips every 10,000 hours.
Even with compliance of the maximum load limits, it’s not uncommon for a crane to tip due to a faulty or uneven foundation. When lifting over the side or corner of a carrier, sometimes the outriggers (external supports that secure the crane to the ground) will raise up off of the supporting surface. This action obviously alerts workers, but just because an outrigger lifts off of the surface does not mean that it’s absolutely going to tip.
This “lift-off” provides its first indication with an apparent gap between the outrigger beam and the carrier frame from which the crane projects. If the crane continues to approach its chart limits with a heavier hook load or increased radius, the outrigger beam and float will begin to rise off the ground.
Why does the crane lift off of the ground even if the load limit is not exceeded?
As crane design has evolved, cranes are being made lighter with less material in order to be more transportable. Though strength and capacity are not necessarily sacrificed, science tells us that a lighter crane that retains its strength abilities will become unbalanced more quickly than a crane with a heavier infrastructure. Ultimately, this creates concern on the job site. Because newer cranes can flex and twist to a higher degree, workers may recognize this as load drift or even lift-off.
There’s no question that working at 90% of load capacity as opposed to 50% of load capacity is going to increase the likelihood of tipping. On the other hand, it can be exceedingly frustrating when flexibility and outrigger lift-off characteristics are understood as tipping when no hazards are actually present. Outriggers lifting off of the ground may indeed indicate overload and an imminent tipping hazard. It’s crucial to know the load limits and check for structural issues in the outrigger, which may produce extreme flexibility.
As a crane operator, this information should hopefully make you more cognizant of your load limits as well as the action that is occurring around you at all times. Knowing the signs of potential tipping as well as being disciplined in your daily preliminary checklist will decrease the chance of tipping and other accidents.