Читать книгу Chainsaw Manual for Homeowners - Brian J. Ruth - Страница 20

Kickback causes many chainsaw accidents. Kickback can occur whenever the upper part (quadrant) of the tip of the guide bar has contact with, but does not cut through, an obstacle while the chain is moving. The chain is moving away from the operator at that point, so contact transfers the power to the bar, which quickly propels the guide bar upward and backward in an uncontrolled arc—often right toward the operator.

Kickback can happen with lightning speed. With a saw at full throttle, the chain can reach speeds upwards of seventy miles per hour. This speed, transformed to the saw’s rotation, means the tip of the bar can reach the operator in ¹⁵/₁₀₀ of a second. No one can react that quickly and an accident is very likely to happen.

The chain brake was designed to prevent such accidents from happening. An inertial chain brake (sometimes called an “automatic chain brake”) can stop the chain in ⁶/₁₀₀ of a second. A manual chain brake that must be pushed forward with the left hand can stop the chain in ¹¹/₁₀₀ of a second. It is easy to see the importance of these safety features.

Avoiding kickback

Most chainsaw accidents result from kickback: when the upper part of the guide bar tip—known as the kickback danger zone—contacts any solid object, the guide bar will jump back toward the operator.

Although some chainsaws have safety features to prevent kickback, handling the saw correctly is the best insurance. Always be aware of the guide bar tip’s location, and never cut with the tip. Watch for objects behind the one you are cutting; such hazards may be obscured by branches or leaves.