Safety Fundamentals for Chain Saws

Chain saws are a fundamental tool for arborists. They also are one of the most dangerous tools and often the one we have the least training on of all the tools in our arsenal. It doesn’t matter if it’s a top-handle, battery-powered saw or a 100cc behemoth with a 3-foot bar, they are all equally dangerous. Here, a volunteer with the Massachusetts Arborists Association makes the final cut on this removal at Appleton Farms in Ipswich, Mass., on Arbor Day 2019. TCIA staff photo.

Let’s start by saying I love chain saws – the bigger, the louder and the sharper, the better. I feel more alive when holding a well-running, sharp saw than at most other points in my day! How many of you also feel that way?

Chain saws are a fundamental tool for folks working in the green industry. They are also one of the most dangerous tools and often are the one we have the least training on of all the tools in our arsenal. It doesn’t matter if it’s a top-handle, battery-powered saw or a 100cc behemoth with a 3-foot bar, they are all equally dangerous.

Since its inception, the chain saw has gone through numerous modifications, some of them to improve cutting performance, but many to improve operator safety. Most significant design changes in the past 30 years have been paid for in blood by chain saw operators. In this article, I’ll explain some of the most significant safety features of the modern chain saw and the reasons for those changes. Most chain saw manufacturers agree these are the basic safety features that should be present and functioning on a chain saw before it is put into operation.

Inertia chain brake: Inertia chain brake refers to its activation with sudden, violent movement of the saw. The chain brake is actually dual-activated – it can also be operated with a push or pull from the hand/wrist. If your left wrist forces the kickback guard forward, the chain brake will activate. Photo courtesy of Husqvarna.

Inertia chain brake

This is the most commonly known and recognized safety feature on the saw. This is to protect the operator from rotational kickback. This is caused when the upper quadrant of the bar (the “no zone”) contacts the wood. The inertia chain brake is designed to activate much like a seat belt. If the saw moves rapidly in any direction, the force or inertia of that movement should engage the brake, regardless of where the operator’s hands are.

This feature should be tested prior to operation by simply holding the saw out at shoulder height and letting the bar of the saw drop onto a log on the ground. The inertia from this should cause the brake to activate. If not, there is most likely a maintenance issue, and the brake band and spring should be cleaned.

The chain brake is also designed to be engaged whenever the operator is moving more than two steps with the saw running, or whenever carrying or starting the saw, to further protect the operator from any accidental cutting incidents.

This diagram shows the location of the safety features discussed in this article. TCIA graphic by Richard May.

Chain catch-pin/peg and hand/wrist guard

These two features work together to protect the operator in the event the chain comes off the bar during operation. Chains travel at incredible speeds, and when a chain comes off the bar, it could potentially wrap around the operator’s leg or come back under the body of the saw and strike the operator’s right hand or wrist. The chain catch-pin/peg was designed to catch the chain as it comes off the bar and use its normal rotational direction and energy to redirect its momentum under the body of the saw rather than around the operator’s leg. The hand or wrist guard was added so that when this occurred, the chain would not come back and strike the right hand of the operator.

Posting of this warning sign was mandated by the U.S. Forest Service to help prevent forest fires. As the saw runs, it creates sparks from the muffler. The spark arrestor is a filter designed to prevent any spark large enough to ignite a forest fire from escaping the saw. The spark arrester in modern chain saws also provides back pressure on the engine that keeps the saw running at peak performance. Photo by Tbmaynard@wikipedia.org.

Spark arrestor

This was mandated by the U.S. Forest Service to help prevent forest fires. As the saw runs, it creates sparks from the muffler. The spark arrestor is a filter designed to prevent any spark large enough to ignite a forest fire from escaping the saw. The spark arrester in modern chain saws also provides back pressure on the engine that keeps the saw running at peak performance.

Modifying or removing the spark arrestor is not recommended. Not only will it get the operator in trouble with OSHA – think California wildfires – but it also will cause damage to the piston and shorten the overall lifespan of the chain saw.

The chain catcher (arrow) helps prevent the chain from being thrown back toward the user if the chain breaks or becomes derailed. Chain catchers are made of aluminum (as shown here) or plastic so as not to damage the chain. A worn-out chain catcher can and should be changed. Photo courtesy of Husqvarna.

Anti-vibration mounts

These mounts are a set of springs or rubber grommets designed to isolate the engine of the saw from the operator handles. When chain saws first came out, they did not have this feature, and a lot of operators developed serious muscle and vascular issues in their wrists and arms due to the constant vibration from the saw. Sometimes it was so extreme they literally had to pry their fingers off the top handle at the end of a day. These mounts dampen the vibration, allowing an operator to cut for a full day with dramatically fewer short- or long-term health effects.

Chain saw spring mount. The handles of the saw are isolated from the engine and cutting bar to reduce vibration for the operator. Excess vibration can cause “white finger,” a vascular issue. The spring mount is part of this vibration-isolation system. Photo by Emrys2@wikipedia.com.

Throttle interlock

This is the plastic piece above the trigger. It is put there so that in order to rev the saw up, the operator must have his or her right hand fully wrapped around the handle and in the correct position to allow for maximum control of the saw during operation. If you can squeeze the trigger without first depressing the interlock, the saw should be taken out of service.

The safety-throttle interlock prevents the chain from being driven if the trigger is accidentally pushed by an obstruction, such as a branch in undergrowth. It also prevents throttle activation when hot-starting a saw on the ground with one boot inside the rear handle. The safety throttle is an additional layer of protection in this case, since the chain brake should be applied before starting a saw in any context. Photo by Emrys2@wikipedia.com.

Conclusion

Every time you pick up a saw, there should be a brief pre-operation inspection to make sure all the safety features are in place and functional. A chain saw remains an extremely hazardous tool that requires no proof of training or competency to purchase. Thousands of stitches are put in people’s flesh every year due to a lack of understanding and respect for this potentially deadly tool. Please take the time to inspect your saw and teach someone else these basics, so we can all tell great tall tales of the biggest tree we ever removed!

Phillip Kelley is a safety team leader at Wright Tree Service and lead instructor with North American Training Solutions, a 10-year TCIA Associate Member company based in Douglas, Massachusetts.

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