Planning Tree Removals and Rigging Loads

Removals are some of the most dangerous work a tree crew does. You are taking apart a heavy, uneven, possibly rotten structure, often next to a house and wires, while it holds people and rope. Many of the ways a removal goes wrong are set up in the plan, before the first cut. A lead climber or crew leader has to look at a tree and work out how it will come down, where each piece goes, what each piece weighs, and whether the wood can take the load.

Reading this does not qualify you to fell, rig, or climb. This work has killed experienced people. You need supervised, hands-on training, repeated practice, and evaluation by a qualified trainer before you make these calls. Crane work and advanced rigging are specialties with their own training. Use this to understand the thinking.

What You Will Be Able to Do

• Choose between felling, sectioning, a lift, and a crane
• Explain the parts of a felling cut and how they fail
• Estimate the weight of a piece before you cut it
• Explain why rigging forces are far larger than piece weight
• Check gear ratings against realistic loads
• List the signs that a removal needs a different plan

Choosing the Method

Start with what the tree can safely take, then what the site allows.

A dead or badly decayed tree often rules out climbing. Dead wood can break without warning, and dead trees of some species turn brittle fast. Vibration from a saw or the shock from a rigged piece can bring down a top. If the tree cannot be trusted, keep people out of it. Use a lift or a crane instead.

Reading the Tree for the Removal

Add these questions to your usual tree inspection.

1. Which way is the weight? Look at lean and at heavy limbs on one side.
2. How is the wood? Sound the trunk and look for decay at the base, at unions, and at the planned tie-in and rigging points.
3. What is the wind doing now?
4. What is under, beside, and above? Think of wires, roofs, fences, septic lids, and soft ground.
5. Where is each piece going, and how does it get there?
6. Where do people stand for every step? Where do they go if something goes wrong?

Felling Cuts

Felling uses a notch, a hinge, and a back cut. OSHA's logging eTool gives good figures for these, though OSHA's logging standard is written for logging, not tree care. Your training and your employer's procedures set the method you actually use.

• Notch (face cut): Cut on the side the tree should fall. Depth is about 1/4 to 1/3 of the trunk diameter.
• Hinge: The strip of wood left between the notch and the back cut. It steers the tree and holds it to the stump for most of the fall. Hinge width is about 1/10 of the diameter.
• Back cut: Cut from the far side toward the notch. With a horizontal face cut, the logging rule places it above the level of the face cut.

Worked example. A trunk is 24 inches across at the cut. The notch goes about 6 to 8 inches deep, and the hinge is about 2.4 inches wide. Cut the hinge too thin, and it breaks early, so you lose control of the fall. Leave too much, and the tree may not fall, or it may split.

Warning: A tree with a heavy lean can split up the trunk during the back cut and kick back at the feller. This is called a barber chair, and it has killed people. Leaners need a technique taught hands-on, not one learned from reading.

Clear your escape path before you cut, at an angle back from the direction of fall. Move away as soon as the tree starts. OSHA's logging rule keeps other workers at least 2 tree lengths from a tree being felled. Do not leave a partly cut tree standing. Do not push one tree over with another. Domino felling is banned under the logging standard for good reason.

A decayed hinge will not hold. If the trunk is hollow at the cut, the tree can go any direction. That calls for a different plan.

Estimating Piece Weight

You cannot rig what you have not weighed. Volume comes first.

Volume in cubic feet = 3.14 x radius x radius x length, with all three in feet.

Then multiply by how heavy the wood is. Green wood is full of water. Many green hardwoods run around 60 pounds per cubic foot, and softwoods usually weigh less. Some species are heavier. Use a species table for your region when the load is close to any limit, and allow for side limbs.

Worked example. A red oak log is 18 inches across and 6 feet long. The radius is 0.75 feet. 3.14 x 0.75 x 0.75 x 6 is about 10.6 cubic feet. At 60 pounds a cubic foot, that is about 640 pounds.

Weight grows with the square of diameter. This table shows a 4-foot piece at 60 pounds a cubic foot.

Double the diameter and you have four times the weight. A climber who is comfortable with a 12-inch piece is working with a very different thing at 24 inches.

Rigging Forces

Rigging is a chain of parts: the piece, the sling, the rope, the block, the rigging point, and the tree below it. A failure of any of these can kill. The load on those parts is never just the piece's weight.

The Block Sees Double

A rope through a block pulls down on both sides. If a piece hangs still, the rigging point carries about twice the weight of the piece, once for each side of the rope. The exact amount depends on the rope angle and on how much friction the rope has.

Shock Multiplies Everything

When a piece falls and the rope stops it, the force is many times its weight. In UK research for the Health and Safety Executive, with the friction device locked, forces at the block were on average 8 to 12 times the weight of the lowered section. The multiple fell as the sections got heavier. A later rule of thumb from drop tests is about 8 times the section's mass plus a fixed amount. Results change with rope type, length, and setup, so use these figures to understand scale, not as a limit you can design to.

Worked example. You plan to let a 190-pound piece drop and stop it hard on a locked rope. At 8 to 12 times its weight, the block could see about 1,500 to 2,300 pounds. A piece the crew could lift between them is loading the stem like a small car.

Those peaks also pull on the stem at an angle, which bends it. A stem that holds a straight load can snap under a side load. Trees have failed at the rigging point and at the base, with climbers in them.

Lowering the Force

• Cut smaller pieces.
• Reduce how far a piece falls before the rope takes the load.
• Rig above the piece where you can. Negative rigging, where the rigging point sits below the piece, means a longer fall.
• Let the rope run a little through a friction device, instead of locking it. This takes a trained operator.
• Keep the rigging point close to the main stem, on sound wood.

Rating Your Gear

Know two numbers for every part.

• Breaking strength: Where a new part fails in a test.
• Working load limit (WLL): The most load the maker says to put on it in use. It is far lower than the breaking strength.

Tree work is hard on gear, so suppliers suggest bigger margins than in other trades. One common guideline uses a 5 to 1 ratio for static loads and a 10 to 1 ratio where a load may fall and shock the system. Block makers often set the WLL at around 20 to 25 percent of breaking strength. Your employer's rule and the maker's data are what count.

Worked example. A rope has a breaking strength of 12,000 pounds. At 10 to 1, you would treat 1,200 pounds as the limit. The 1,500 to 2,300 pounds from the shock example is beyond that, so you need a smaller piece, a shorter drop, or a controlled run. Knots also weaken a rope, and so do worn spots and tight bends.

Use rope, slings, and blocks rated for rigging, and inspect them on every job. Never rig on a climbing line.

The Rope Operator

The person on the friction device controls the load, so that person needs training and a clear view or a clear signal. Run through the plan for each cut together: where it lands, how much rope to let run, and what "stop" sounds like.

Stay out of the bight, which is any loop or bend in the rope that could snap tight. Do not stand between the load and the block, under the piece, or in line with a rope that could break.

Cranes

A crane can take a piece straight off a dangerous tree. It also adds a different set of ways to get hurt. Crane removal is a specialty, and it takes a qualified operator, a trained rigger, and a climber who has done it before.

• Know the pick weight. Estimate it low and you can tip the crane or overload it.
• Do not shock the crane. A piece that drops onto the hook after the cut can damage it or bring it over.
• Use a clear signal system. One signal person talks to the operator.
• Set up on firm ground. Check for buried utilities, soft ground, and overhead lines.
• Workers on the hook have strict rules. Do not assume you may ride.

Which federal crane rules apply can depend on the job, and states may add operator rules. Your employer needs to work that out before the job starts.

When the Plan Must Change

Stop and rethink if any of these turn up:

• The base sounds hollow, or a tie-in looks weak
• Wind picks up
• A piece does not act the way you planned
• Anyone is unsure of the next step
• A line, a person, or a vehicle is in a new place
• Someone on the crew is tired or rattled

Anyone on the crew should feel able to call a stop. A re-plan takes minutes.

Common Mistakes

Check Your Understanding

1. A trunk is 30 inches across at the cut. About how deep should the notch be, and how wide is the hinge?

A notch depth of about 7-1/2 to 10 inches, and a hinge of about 3 inches.

2. A crane operator asks you for the pick weight of a bare trunk section that is 16 inches thick and 10 feet tall. You have no species table with you. What figure do you give, and what do you say about it?

The radius is about 0.67 feet. 3.14 x 0.67 x 0.67 x 10 is about 14 cubic feet, so about 840 pounds at a planning figure of 60 pounds a cubic foot. Say that it is an estimate. Check a species table if the pick is anywhere near the crane's limit.

3. A climber wants to cut pieces twice as thick as before, with the same length, on the same rigging. What happens to the load?

Weight goes up about four times, because it grows with the square of diameter. Forces at the block go up a lot too. Rework the plan.

4. A dead tree stands next to a garage, and the top shakes when you sound the trunk. What do you do?

Do not climb it. Look at a lift or crane, and keep people out of the fall zone until a qualified person makes the plan.

Key Takeaways

• Choose the method from what the tree can take, then from the site.
• A notch of 1/4 to 1/3 of the diameter and a hinge of about 1/10 are common figures.
• Estimate weight first, and remember that it grows with the square of diameter.
• Shock can multiply load many times, and blocks see about double.
• Use smaller pieces, shorter drops, and rated gear.
• Hands-on training comes first. Reading never replaces it.