What is chain shot, how does it happen, and how do we ensue operator and bystander safety?
Oregon educates on harvester chain shot. Chain shot is the high velocity separation and ejection of a piece or pieces of cutting chain from the end of a broken chain in saw chain based mechanized harvesting systems. Chain shot potentially exposes both machine operators and bystanders to a risk of serious injury or death. Chain shot typically occurs near the drive end of the cutting system but can also come from the bar tip area.
First, the saw chain breaks. Second, after a saw chain break, the “free” end of the saw chain begins to whip away from the break. Third, if the saw chain is not contained by the saw box or a chain shot guard, the broken saw chain’s free end can speed up rapidly, carrying immense dynamic energy. Finally, at the peak of the whip, saw chain pieces may break loose and be ejected at high speed.
Although the "Shot Cone Zone" reflects the most likely chain shot path, deflections can occur, substantially expanding where chain pieces may travel. To minimize risk, operators should keep out of the Shot Cone Zone. Ground personnel and bystanders should be at least 230 feet away from cutting operations and out of the Shot Cone Zone.
The following best practices will increase your safety and the life of your cutting system. Do not use saw chain that:
- Has broken twice or is severely damaged.
- Has excessive saw chain stretch or has broken or cracked components.
- Has loose rivet joints—if you can rotate the rivets with your fingers, they are too loose.
Important operational recommendations are as follows:
- Never engage in a cut with yourself, ground personnel, or bystanders in the Shot Cone Zone.
- Always cut as close to the ground as possible to reduce the distance that any potential ejected pieces could travel.
- Your cutting systems operates in challenging environments and depend on sufficient lubrication to minimize wear and extend the life of operation.
In the next issue of Logging-on we will look at techniques to minimise the risk of a chain shot event. Source