In the last issue – literally, since TCIA’s monthly safety newsletter is no longer being published – of the Tree Worker (July/August 2020), the page-12 article, “Rope and Pulley … a Dynamic Duo,” definitely caught my attention.
With all due respect to the great staff at TCIA responsible for so many years of solid information, this article would have been a far more effective learning tool if it had been presented as a “What’s Wrong with This Picture?” piece, because there is not much right about it as presented.
- As pictured (Image 1), the lowering line under tension is going to exert a side pull on the “generic lowering device” that no Hobbs, Good, Stein or any other brand of tree-mounted device is designed for.
Running the rope as illustrated straight to the lowering device is a great way to ensure a really bad day. (Image 2).
I am going to say this again – No lowering device is designed to function properly when subjected to a side pull!
It is “OK” to fix a block to the base of the tree being rigged to lead the rope off to another tree that the lowering device is anchored to, but rarely necessary. If you do this, you have to make sure the “base block” is secure. When the system is loaded, the block will be subjected to an upward pull. You do not want the block to slide up the trunk.
Depending on the distance the anchor tree is to the rigged tree, a base block may not be necessary. Quite often, you could eliminate the extra link of running through a base block and go straight from the top block in the tree to the fairlead above the spool. (Image 3)
- When using a lowering device mounted on a tree different from the one being rigged, it is imperative to set a block above the device so the rope enters the spool from 12 o’clock (dead vertical).
All lowering devices are designed for maximum strength when so loaded. Going directly to the spool from 3 o’clock will subject the device to a potentially dangerous side-loading that may result in a catastrophic failure.
This commandment is also applicable to rigging from a lowering device mounted on the tree being removed. Wide-spreading trees like the southern live oak quite often require a fairlead to prevent the rope from entering the spool at an off angle. (Image 4)
Another thing wrong about the scenarios depicted is perpetuating the erroneous belief and practice that the line-handler must be close to the device when working off the tree being rigged. (See Image 1)
Ed Hobbs invented his original lowering device, aptly named the Hobbs Lowering Device, so that the operator could stand as far away from the device as needed for safety. And yet the illustration shows the line-handler right up close to the device while standing in the drop zone. It does not have to be that way and shouldn’t be – ever!