In our previous blogs, we reviewed the basics of crane safety, going step by step through everything from setting up to landing zones. Here, we examine the varied types of chokers and slings, the best use for each and how to stay safe throughout the process of fastening them.
What Are Chokers and Slings?
Chokers and slings are the systems used to secure tree limbs for cutting. They are set in place by the arborist performing the cut, who are either put in place with a crane or with proper tree climbing technique.
The choker is the piece that is actually secured in a loop around the limb. The sling, meanwhile, describes the entire configuration. There are multiple ways to set up a sling. An arborist should know how to set up a variety of slings and when to employ each. Slings can largely be broken up into two categories: single- and multi-leg sling configurations.
A single-sling configuration uses only one choker for a sling to stabilize a limb. These configurations are easier to create and work well for lighter limbs. The safety risks of this kind of setup remains, however. To maintain crane safety, the arborist should ensure that the choker is positioned directly beneath the headache ball and at the center of gravity of the limb being cut. Double-check that the choker is secure once it is in place to ensure maximum safety.
Multi-Leg Sling Configurations
Sometimes one choker isn’t enough to safely and securely take down a limb. Adding two or more chokers can reduce the speed at which a limb comes down and increase control, so that you can be sure that it falls in the landing zone. Each choker attaches to the same headache ball. This setup is called a multi-leg sling configuration.
To safely create a multi-leg configuration, ensure that the headache ball is positioned over the center of gravity of the limb for maximum security. Adjust each leg of the sling accordingly to ensure this. Even with a second choker, it’s important to ensure that the limb being removed is under the sling’s Safe Working Load.
Once the configuration is set up, the arborist should check that each sling’s angle is appropriate. Sling angle is important because a wider angle means increased tension. The tension of the sling will have a huge impact on the overall capacity. Calculating the angle incorrectly could have devastating consequences. Most arborists should look to create a 60-degree equilateral triangle between the two legs and the limb that is being cut as a starting benchmark and measure from there. In some cases, this may not be possible depending on overhead clearance.
While single and multi-leg sling configurations may vary in some ways, the general tenets of good arborist crane safety remain steadfast no matter the method.
Once a sling is set in place, the same chainsaw safety protocol generally applies. This includes constant radio communication between the arborist and the crane operator and being sure to cut in a controlled manner.
While there are different kinds of chainsaw cuts that can be used, depending on the circumstances, it is almost always best to avoid using a snap cut. A snap cut is when the crane operator uses the force of the crane to pull the limb off the tree. This technique carries a higher safety risk because the limb is harder to control. In every case, workers on the ground should wait until the branch has fallen before entering the landing zone. Chokers should only be removed from the limb after it is on the ground and the all clear has been given.
Tree care professionals run a risk any time they use a crane for tree limb removal. Crane safety protocol is important and can help to mitigate potential injury to both workers and pedestrians. This ultimately prepares the limb to be cut, so using a proper sling configuration is essential. Arborists should know how to choose the correct type of sling, estimate the weight of the limb and check the leg angles, in the case of multi-leg sling configurations. Even then, good communication and general crane safety protocol must be followed at all times.