Felling Snags
THIS IS A VERY DANGEROUS THING TO DO. IF YOU DO NOT HAVE PLENTY OF EXPERIENCE---AND HOPEFULLY TRAINING AS WELL---DO NOT TRY THIS. THIS IS HERE PRIMARILY TO CONVINCE YOU TO RECOGNIZE SUCH A SITUATION , THEN TO EITHER NOT DO IT; OR IF YOU'RE CRAZY ENOUGH TO THINK YOU CAN, GET PROPER TRAINING!
Snags are dangerous trees---diseased, rotten, with weak limbs, fires in their crowns, etc. They must be put on the ground without anyone being hurt ... before someone else gets hurt by them.
Snag-falling is a very dangerous job. Pity the guys and gals on firelines out West where the snags are large and mean! But all firefighters sometimes face large trees by the side of the road, brought down, or nearly brought down, by storms, etc.
So first of all look for wires that have gotten tangled, or could be entangled, in that tree or others that tree might affect. Wires are bad not just because they may affect the fall of the tree, but because they very well may be "hot"---charged with electricity. Just because the wires are broken---and even if the power company has shut the power off---the lines could be charged by some idiot with an emergency generator that has been wired wrong. If these conditions may exist, leave those situations to the power company ---they've got the equipment and trained workers to deal with it.
By definition, these trees are not merchantable. They will not be used for lumber nor any of the other products that can come from the forest. Therefore the felling of them doesn't have to be concerned at all about conserving wood by cutting low stumps, etc. Just get the tree on the ground without getting hurt!
If something goes wrong---get the hell out of there. For that reason, cut with a high stump---high enough that you are standing so that you can run without having to stand up from a crouched position first. And don't try to force a tree to go in some direction it doesn't want to go---pounding away on a wedge might knock something down. Assume that the hinge might fail---because it's a sick tree, remember?
It's often been suggested that it would be a good idea to have someone else watching, to notify you if a branch starts to fall. Unfortunately, a person's reaction time is not fast enough to notify the cutter in time.
These links point to more information on the subject. The wildfire agencies also provide training. Contact them.
Here are a couple of sites with more info, from the USFS: