Chainsaw shot is the high-speed separation and ejection of a piece or pieces of cutting chain from the end of a broken chain. Chainsaw shots occur after the initial break and is often caused when the chain strikes something, such as the saw box, causing pieces from the chain to break loose. While chain shots can travel in any direction, the pieces of broken chain usually travel along the plane of the saw bar. However, a chain shot can also spread out from the plane of the saw bar in a cone-like pattern. This is sometimes called the “cone zone” and starts at each end of the saw bar and increases in circular area away from the saw where the chain shot is most likely to travel.
Chainsaw shot potentially exposes both machine operators and bystanders to a risk of serious injury or death. Chainsaw shot typically occurs near the drive end of the cutting system but can also come from the bar tip area.
Sequence of events
|After a chain break...|
|The free end of the chain begins to whip away from the break.|
|If the chain is not contained by the saw box or an energy-absorbing guard, the broken chain's free end can speed up rapidly and carry immense dynamic energy.|
|At the peak of the whip. chain parts may break loose and be ejected at high speed, especially if the free end of the chain strikes the saw box. Chainsaw shot can cause chain parts to be thrown in many directions, especially along the plane of the saw bar.||Fragments have been measured at between 180 and 310 m/s under laboratory conditions.|
Figure 1: Diagram of chain shot from Oregon's The mechanical Harvesting Handbook.
Can chainsaw shot be eliminated?
In simple terms NO. Properly designed chain shot guards and shields reduce the danger of a chain shot from the drive sprocket area. However, there is currently no known way to place similar guards in the bar tip area without significant disruption to the cutting operation.
To minimize risk, operators should keep out of the Cone Zone. Ground personnel and bystanders should be at least 300 feet away from cutting operations and out of the Cone Zone.
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