Chain Saw Safety and Selection for Arborists
A PDF of this white paper can be downloaded here.
The proper size and type of saw depends on the nature of the work that you are doing. Are you pruning small, or large branches? Are you working from an aerial device, climbing, working from the ground? Are you removing a tree; in sections aloft or the whole tree from the ground? What size of wood are you cutting? In general, you want the saw to have just a little more power than you need on a daily basis. If the saw is too small, you will overwork the saw and yourself. If the saw is too large you will fatigue faster and have less control of the saw and bar.
One of the key factors in saw selection is to make sure that you are purchasing a professional-grade saw. These saws are designed to have higher performance, more power, last longer, and cost a little more too usually. The consumer/homeowner saws are intended for occasional use, not daily like a professional arborist would use them.
Chain saw manufacturers have different classes of chain saws that are based on engine size, as listed in cc's and overall design/type. We have always viewed them in three broad categories:
Although you need to know it, this paper will not cover saw chain sharpening, engine tuning or the other kinds of saws.
Saws to be used aloft:
These saws are smaller, lighter, balanced and designed to be used inside of a tree whether from a bucket or while climbing. Some of these have a handle on the top that make them easier to use inside the tree, but all of them are designed to be used with two hands, with a firm grip (thumb wrapped) around the handle, more on safety in a bit.
These saws are usually in the 25-35 cc range and are called any number of things:
- Trim saws
- Climbing saws
- Bucket saws
The bar length ranges from 12â€-16â€ usually but can vary depending on the make/model and engine size. They are designed to cut smaller diameter wood; branches and small to medium diameter stems. Many of them have an attachment point on the rear of the saw that is intended as a connection point for a lanyard.
These saws are generally larger, in physical size as well as engine size than the saws used aloft. Bar length varies but can range from 16â€ up to five or six feet. They have rear handles and some additional features for cutting larger diameter wood. These saws can range from 40-125 cc's.
Other than being larger, these saws have some additional features that the aerial saws often do not, including:
- Compression release/decompression valve
- Heated handles
Ground saws are designed for extended cutting and use in larger diameter wood.
Saw Chain and Guide Bars - When purchasing a new saw, it should come with the correct guide bar and chain, but there can be issues later as you replace worn parts if you get the wrong ones. Some wrong combinations of bars and chains will not work together and some will work, incorrectly, causing wear to the saw.
Saw chain primer - Some key terms and concepts that you need to know: Chain pitch- the distance between any three rivets, divided by two. Some common chain pitches you will see on professional grade chain saws are:
- Â¼ inch
- .325 inch
- 3/8 inch
- .404 inch
Chain gauge- the thickness of the drive link of the chain as it fits in the guide bar groove. Common gauges are:
- .043 inch
- .050 inch
- .058 inch
- .063 inch
As we mentioned earlier, this will not be a complete instructional paper on how to sharpen your saw, but you need to know at least the basic components of the cutting tooth.
- Depth Gauge (raker)-the leading edge of the cutting tooth. This regulates how thick the woodchip removed will be. If filed too low, the saw will chatter and jump as it tries to take too large a piece. If not filed enough, the chain will not take a large enough piece of wood and the operator will have to force the chain into the wood, actually burning through instead of cutting.
- Gullet-â€œUâ€-shaped space behind the raker.
- Cutting Corner or point-Sharp edge behind the gullet. This starts the cut into the wood fiber.
- Side Plate-The vertical surface beneath the cutting corner. This severs the long fibers of the wood, does most of the work. Angle should be near 900 for most styles of chain.
- Top Plate-The flat upper surface of the cutting tooth.
- Chisel Angle-Separates the wood chip from the kerf, regulating the cut width by how far the tooth is allowed to move to the side. The more the top plate is angled, the wider the kerf. The chisel works together with the depth gauge.
- Filing Angle-Line on back of top plate that shows the proper angle to sharpen.
Guide bar primer:
The key components of the guide bar are:
- Motor mounting holes-At rear of bar, fit over bolts on saw to mount bar and cover to saw.
- Bar and chain oiler hole-Small holes near upper surface of bar, allows bar and chain oil to pass into the groove of the bar, lubricating both.
- Rails-Raised edges of the bar, with a groove between them, allowing the chain to run in the bar.
- Sprocket-Rotating portion at the end of the bar.
General maintenance of saw chain and guide bar:
Always wear gloves when you are doing any maintenance on your saw! The chain and bar should be properly matched and the chain should be properly tensioned. Flip the bar every often to ensure even wear, there is often more pressure placed on the bottom of the bar as you use it.
Preparing to use the saw:
We now have the correct saw, saw chain and guide bar. The next step is to make sure that the saw is ready to use, and we are ready to use it. First, us, we need to be physically and mentally ready to use a chain saw. We should be well rested, fed, hydrated and not under the influence of any chemical that would interfere with safe use of the saw.
Next, we need to have proper Personal Protective Equipment (PPE) - , that is properly fitted to us, in good condition and is, at least relatively clean. Starting at the top and working down, we need:
- Head protection-All arborist head protection, helmets, need to conform to ANSI Z89.1. Arborists working in proximity to electrical conductors must use Class â€œEâ€ helmets.
- Eye protection-All eye protection shall conform to ANSI Z87.1 and needs to worn during arboricultural operations. Improvements in helmet design now include shields that can be dropped to protect the eyes. Some of these are ANSI Z87.1 compliant but only when they are pulled completely down to protect the eyes. If the shield is up during work, safety glasses conforming to ANSI Z87.1 must be worn.
- Hearing protection - Hearing protection designed to reduce noise levels to acceptable levels, either muff or plug style, shall be worn.
- Cut resistant leg protection-Leg protection meeting the minimum requirements laid out in ASTM F1897 shall be worn when operating a saw on the ground. The protection can be of the chap or chap-pants type and the protective material should cover from the top of the thigh (inseam) to the top of the foot and wrap around the calf. They should be fitted to the individual, not too tight or too loose and kept relatively clean. Cut resistant material contaminated with petroleum products (gas, bar oil, etc.) can fail to provideprotection.
- Sturdy work boots.
The next step is to inspect the saw.
- Look for any leaking fluids, fuel or bar oil. Inspect all nuts, motor mounts, moving parts for defects or tightness.
- Check the start cord-With the saw in the off position (If possible), slowly pull the starter cord all the way out. Inspect the cord for damage and make sure that it is the correct length. Usually, about 30 inches correct but check with the manual. If the cord is too short, you may not get enough pull or too much and break the cord.
- Check air filter-Make sure the filter is clean and installed properly. Dirty air filters are one of the leading causes of a poorly running saw. â€¢ Check bar, chain and sprocket.
- Make sure the saw is filled with the proper fuel mixture and bar oil.
- Inspect all safety features-If the saw is missing any of these components or they are not operational, the saw is not safe to use!
- Functioning, easily accessible on/off switch
- Manual chain brake-Make sure that the chain brake engages when the hand guard/kickback guard is pushed forward, and releases when pulled back.
- Inspect secondary chain braking mechanism in rear handle if so equipped.
- Inertial chain brake (if so equipped).
- This can be checked when the saw isn't running by standing over a log or stump, releasing the chain brake and while maintaining a full grip on the rear handle of the saw, let go of the front handle, allowing the saw bar to drop onto the piece of wood. You should hear a â€œsnapâ€ as the brake engages but you can check to make sure that the chain doesn't turn.
- Ant vibration features-These are springs or other vibration dampening features the separate the power head from the handles. If they are missing or defective, you will experience more vibration and fatigue.
- Chain catcher-On the underside of the saw, there will be a soft metal or composite piece that is designed to limit the movement of a chain if it comes off the bar or breaks while in use.
- Hand guard-Flat piece of the saw under the gripped portion of the rear handle, often part of the fuel tank that is designed to further protect the hand if a chain comes off the bar. Additionally, this is often a spot that can be used to hold the saw on the ground with one foot when starting, more on that in a bit.
- Throttle interlock-A component on the top of the gripped portion of the rear handle that is connected to the throttle/trigger. Designed so your hand must be on the handle, depressing the throttle interlock before the trigger can be used.
- Spark Arrestor-Metal screen in the exhaust system designed to prevent sparks from being emitted with the exhaust, potentially starting fires.
Before the saw is started, we need to understand some of the basic forces that we will encounter when using the saw. These forces are created because of the fact that the chain rotates around the bar. The chain moves forward from the top of the bar, rotates around the bar tip and then returns back along the bottom of the bar. We need to have a firm grip on the saw and either proper footing or be properly positioned in the tree or aerial lift before beginning the cut to make sure we aren't thrown off balance. There are four main concepts, or forces that are often discussed, and are detailed below:
- Push back-When cutting with the top of the bar, the chain saw will be pushed back towards the operator.
- Pull forward-When using the bottom of the bar, the saw will be pulled forward.
- Kickback- As the chain rotates around the bar there is potential for the saw to be forced back violently towards the operator. There are two main types of kickback; rotational and linear.
- Rotational kickback-Occurs when the upper quadrant of the bar, called the kickback corner, contacts a hard surface while the chain is spinning. This happens because as the chain rotates around the end of the guide bar the cutting point contacts a piece of wood for example and as the raker isn't there to limit the size of the piece, the chain stops at that point. The energy from the rotating chain is transferred back upwards towards the operator as the chain encounters an object in the kickback zone.
- Linear kickback-This type of reaction usually occurs when cutting larger diameter wood, often in the tree with guide bar horizontal. As the saw moves through the wood, creating space, or kerf, the wood can drop, pinching the saw. As this happens the energy from the rotating chain is transferred back into the bar, pushing it straight back out towards the operator.
- Attack corner-Not really a force, but is often included in the discussion of forces and how to use the saw bar. This is the lower quadrant of the bar, which is used to initiate bore or plunge cuts.
Starting the saw
Always wear chaps, and all appropriate PPE when holding or working near a running chain saw.
- 1. Chain brake is set. Make sure the brake is employed, before starting. Check it, twice if you have to.
- 2. Depress compression release if saw is so equipped. The larger saws have a button you can press to open up an airway to the cylinder so it is easier to start. This way you are not fighting the force of making the engine turn and the force of compressing the air inside the cylinder.
- 3. Turn saw on.
- 4. Choke as needed. Check the operator's manual to be sure you are using the choke correctly.
- a. Hot & Cold Starting
- i. If the motor is cold it should be started at full choke until it pops, then set to high speed idle until it starts, then depress the throttle trigger once to bring it down to idle. If you do not press the trigger and bring the saw back down to slow idle you can damage the engine and chain brake (think about stepping on both the accelerator and brake in your car at the same time).
- ii. If the motor is warm you should set the choke to high speed idle or partial choke until it starts, then depress the throttle trigger once as soon as it starts to bring it down to idle.
- 5. Two best methods to start (always have two hands on the saw when starting with the left elbow locked). The key with proper, safe starting is to not â€œdrop startâ€ the saw. A drop start is when you push the saw away from your body with one hand while on the starter cord with the other hand. The key to doing this safely is to have the elbow locked on the arm that is holding the saw (Not the arm pulling the starter cord).
- a. Ground start- (For rear handled saws) Step into handle with your right foot, hold the front handle with the left arm with the elbow locked and pull straight up with the right hand.
- b. Leg clamp-Trap handle/body behind right knee, keep left arm straight and elbow locked and pull.
- i. Variations of this method can be employed to safely start the saw while in a tree on spurs, rope and saddle climbing or working out of an aerial lift.
Now that the saw is running and warmed up a little bit, we need to make sure that it is tuned properly.
- Rev up the engine, squeeze the trigger all the way, and listen for the â€œflutter.â€
- Release the trigger and let the saw come back down to idle, the chain should not be turning at idle RPM.
- With the chain brake engaged, roll the saw over and around and listen to see if the engine RPM's change. If the saw is out of tune, when you roll it over and back to level fuel can pool and then flood the cylinder.
- Release the brake and squeeze the trigger all the way. The saw should rev up to full RPM's quickly. If it is slow to rev or sputters, it is out of tune.
Using the saw (General)
The key to safe and efficient chain saw use is to maintain control of the saw, with both hands, at all times. Additionally, below are some general points for use:
- Always keep both hands on the saw with the thumb and forefingers wrapped on the handles at all times while the saw is running and the chain brake is off.
- Use the chain brake as a parking brake; engage it if you are talking more than 2 steps, or moving in the tree or bucket.
- Keep the saw as close to your body when cutting, it is easier to control. You will also fatigue faster if you hold the saw away from your body.
- There are no left-handed saws; the right hand operates the throttle.
- Whenever possible, position your body to the left of the saw bar, this will reduce the chance of coming into contact with the saw in case of kickback.
- Start all cuts at high rpms, otherwise the chain may catch and throw your balance off.
- Keep your chain sharp and let the saw do the work, you shouldn't have to force the saw into the wood.
- Be aware of what and where you are cutting, pay close attention to the tip of the bar, the kickback zone. Avoid contacting the kickback zone while cutting, and avoid putting the bar into the ground.
- Try to bend your knees if you are cutting close to the ground and not bend at the back.
- Avoid using the saw above your shoulders, you will have less control and will fatigue faster.
- Keep your feet apart for better balance when you are on the ground or in the bucket.
There are many finer points of using and maintaining a chain saw but this paper should get you started in the right direction. This paper is not meant to replace training and there may be situations where the material presented here may not be appropriate.
Authored by Tim Walsh