Chainsaws - Useful and Dangerous Tools
Proper training is required to use a chainsaw safely.
2016 Fallby Peter Kolb
Extension Forestry Specialist, Montana State University Extension
Anyone who has worked with or around trees and forests has probably used, or at least been tempted to use, a power saw, also known as a “chainsaw.” The convenience of being able to cut through a tree trunk or branch in several seconds versus spending a strenuous hour with a handsaw makes a chainsaw an incredibly useful tool. However, the fact that this tool is basically a motorcycle engine with a cutting blade attached that can be dangerous without proper training, should make a person think about a purchase and what training is needed to use it safely.
Chainsaws come in a wide variety of sizes and power options, ranging from very light electric powered saws to ten pound machines with yard-long cutting bars, designed to efficiently cut through 3- to 5-foot diameter logs. New chainsaws are expensive, ranging from several hundred to over one thousand dollars depending on their power, construction, and features.
In general, the majority of chainsaw accidents happen to casual users who purchase a smaller saw for trimming trees, cutting firewood, or clearing access roads. This may be because the smallest electric power saw has more torque than a world-class weightlifter can control when the saw is not used properly. Modern saws have many safety features designed to reduce injury to the user (Figure 1), but the very purpose of the saw – to cut through trees – makes it impossible to protect the user from the most dangerous part, the chain.
A chainsaw operates much like a motorcycle. The motor in the main housing turns a sprocket at the base of the protruding blade (called a bar) that pulls a chain with sharpened teeth around the outside of the bar along a special groove. Each tooth is a razor sharp curved chisel that is engineered to grab into wood (or other material) and pull itself into the wood, chipping out a chunk. This is designed so the saw will pull itself into and through wood rather than fatiguing the user who otherwise would have to push the bar through the wood. When the chain is moving at full throttle, teeth move through wood at the rate of about 10 teeth per inch of wood per second, each gouging out somewhere between ¹/8 to ¼ inch of wood. That translates to about ½ inch of flesh or bone per tooth, or about four inches of leg per second.
Another hazard, called kickback, happens when the tip of a running but poorly held saw touches a hard surface. The force of the spinning chain flips the saw backwards toward a users face or shoulder, potentially inflicting injury or death. Even with a proper grip on the saw, a user’s legs and feet always remain within easy range of the sawblade and account for about 40 percent of chainsaw injuries.
Knowledge of such accidents (more than 28,000 in 1999 across the U.S. according to the Consumer Products Safety Commission) prompted chainsaw engineers to add safety features that reduce the chances of terrible accidents. The first is the chain-brake and handguard on top of the saw. This feature protects the top hand from debris or slipping off the grip onto the cutting bar, and more importantly it is a leveractivated brake that stops the chain from rotating should the saw kick back. Another innovative feature is the anti-kickback chain configuration that has an extra non-sharp tooth built into the chain between each cutting tooth that deflects the rotating chain's power in a kickback situation. Although this feature may slightly impact the chain's cutting efficiency (depending on the saw and wood being cut), it is a highly recommended feature for the novice or occasional user, which the majority of users are. Even for experienced users, being in tune with a saw requires daily use and constant physical conditioning. Thus, taking a two-month break after using a saw puts anyone right back in the novice category when they pull it out and start it up.
There are additional safety features that most modern saws have. These include anti-vibration shock absorbers in the handles to reduce fatigue and nerve damage to hands; a chain-break under the saw to catch a broken chain before it wraps around your lower hand; a throttle brake that prevents the saw from powering up unless you have a firm grip on the back handle and throttle; exhaust that blows wood chips away from the face; a spark arrestor that prevents a saw from throwing sparks and starting fires; and a tip guard on the saw bar that prevents kickbacks, though this feature greatly inhibits sawing ability and is not too common anymore.
Additional external safety features that the user must have are 1) eye protection, 2) hearing protection, 3) saw chaps that protect the legs, ankles, and groin/femoral artery, and 4) a hard hat to protect the head and face from falling debris, kickbacks, and flying debris. Helpful additional features are slip- resistant gloves and hard leather or steel-tipped boots with gripping soles.
Using a chainsaw is hard, physical work and the user should have the necessary strength and coordination to use it. If it is an effort to lift the saw and hold it in a cutting position for more than 5-10 minutes at a time, either a lighter saw should be used or the work turned over to a professional. When a saw is too heavy, the user tends to lunge the saw onto the object they wish to saw rather than move the saw in an easy, controlled manner. Breaks should be taken to avoid muscle fatigue and to properly maintain the saw.
One of the biggest safety issues is a chain that is too loose, which is determined when the saw is off. The ideal tension allows for a dime or penny to barely fit under the chain when it is stretched away from the bar. All chains loosen with use and should be periodically tensioned. It’s important for a user to learn how to do this before using a saw. A loose chain or lack of chain lubricant will cause a chain to pop off the bar or to break.
As with any tool, users should practice using the chainsaw in a controlled setting before using the saw in rough terrain or more difficult circumstances. Stretching toward the object to saw decreases control, thus it is best to step closer and be deliberate about where to cut. The final two tips are: 1) make certain anyone helping stays at least four feet from the furthest cutting reach the saw operator has, preferably 10 feet away in case the operator trips or falls, and 2) be wary of used saws that do not have modern safety features. Older saws may be considerably cheaper to buy, but many lack proper safety features and may have broken parts, metal fatigue, or worn out parts that make them unsafe.
More information about proper chainsaw use can be found online by viewing YouTube videos developed by major brand manufacturers of chainsaws or by visiting the MSU Extension Forestry website under chainsaw safety awareness at www.msuextension.org/forestry/videoresources.html.