Safety Recommendations

Chains on mechanical harvester saws can travel 15,000 revolutions per minute (rpm.)  Higher chain speeds with attendant power input generally equates to faster cutting speeds but faster cutting speeds mean increased wear, shorter service life and increased chance of chain breakage and injury. Chain shot whistling through the air has as much kinetic energy as a bullet fired from a rifle.

Chain shot can occur when chains are worn, damaged, repaired with used linkages or operated at speeds beyond the manufacturers recommendations.  The direct hazard to the equipment operator occurs when the plane of the saw bar is facing the cab, placing the operator in the line of fire should a chain failure occur.  Employers should create a system of maintenance that reduces the likelihood of chain breakage.

Is Chain Shot a Common Occurrence?

There has been a number of investigated chain shot incidents in the forest industry.  Swedish researchers estimate that a chain shot might occur in 1 in every 50 chain breaks (Hallonborg 2002.)

In British Columbia a harvester operator sustained severe abdominal injuries when he was struck by a chain link that passed through a 1/2" poly-carbonate cab window. The WBC investigation:

Another worker was using a manual chain saw to cut a dead stump when the chain broke.  The broken linkages flew through the air and struck another worker about 35' away.  The chain piece removed in life saving surgery had caused injuries similar to being shot by a bullet.

In addition, workers have reported near misses after nearly being struck by pieces of chain linkages released from equipment operated up to 300' away.

How to Reduce the Chance of Chain Shot Occurring:

There are a number of ways to protect yourself from being injured by chain shot including:

  • Follow Manufacturers Guidelines for Use
  • Installing Proper Guarding
  • Positioning & Training
  • Purchasing Decisions

Follow Manufacturers Guidelines for Use

  • Keep the chain tensioned properly
  • Don't repair the chain with used linkages or hammered rivets, often these contain small fractures that weaken the link and increase the possibility of breakage
  • Chains should be inspected for damage, particularly on drive links, before sharpening
  • Chains should be randomly inspected after being sharpened and prior to being installed
  • Inspect the saw for damage/wear to the sprocket, bar and chain
  • Keep the bar and chain adequately lubricated
  • Inspect the chain before replacing, even new chains can be defective
  • Check the chain to make sure it is designed for the cutting speed of your saw
  • Don't overpower the chain; higher cutting speeds wear the chain faster and may contribute to chain breakages
  • Operators and workers responsible for chain maintenance effectively communicate

Install Proper Guarding

Fit harvester head with a chain catcher. This device may reduce the whip like action that produces chain shot by absorbing the kinetic energy released from the chain breaking. To ensure the safety of harvester operators, purchasing harvesters with at least 1 1/4" (32mm) poly-carbonate laminate would be the most effective.

Positioning & Training

While many operators cross cut the stems immediately in front to see if the cuts are being properly made, this positions the saw blade toward the cab and directly places them in the line of fire should the chain break. Re-position the stem for cross cutting so the saw does not point towards the cab.

Workers on the ground around the cutting area should be sufficiently away (70m/230ft) from the cutting and aware of the direction of the chain so they can be positioned on the opposite side to avoid being struck should the chain break.

Purchasing Decisions

Perform a risk assessment when purchasing new equipment to consider if engineering designs can reduce the risk to the operator.  Ask manufacturers what designs are in place to reduce risks to the operators.

Chain shot remains a significant issue and it is important to be vigilant in reducing risks.  On August 12, 2010, a 47-year-old timber harvester operator (employed by a logging company in Washington State, USA) was fatally injured when he was struck in the neck by a broken saw chain link while processing a Douglas-fir tree and the cutting chain experienced chain shot.  The Washington Labor and Industry investigation:

Ways to Further Reduce Likelihood of Chain Breakage:

  • Maintain the whole cutting system not one element of the cutter unit at a time.
  • Avoid fitting new cutter components with worn equipment as this dramatically shortens the life of the new component.
  • Keep chains sharp, maintain correct depth gauge clearance.
  • Don't continue to cut with blunt cutter unit or with no lubrication.
  • Check for chain stretch and replace as necessary.
  • Repair chains using correct components - replace whole chain after second chain breakage.
  • Maintain bar - dress and reverse regularly to balance even wear.
  • Monitor wear on sprocket - use the 6 chains, 3 bars, 1 sprocket ratio as a guide for total replacement.
  • Ensure correct chain tension throughout the operation cycle - auto tension systems provide ultimate chain life and optimum cutting efficiency
  • Ensure adequate lubrication: use good quality, clean bar lube, use clean filling utensils.  Treat it like you would treat your hydraulic system, keep bar lube holes clean.
  • Allow main saws and top saws to warm up before operating: cycle saws six times at low speed. Do not allow saw motors to run at speed with no load for longer than 5 seconds.
  • Maintain correct saw motor RPM and chain speed, bar out speed and bar pressure (refer to your machine's owner's manual or contact the manufacturer for advice.)

(Sources - BC Forest Safety Council, Washington State Labor and Industry, Waratah Forestry Equipment, Forestry Research Institute Sweden, SMP Svenska Mankinproving AB, Washington Fatality Assessment and Control Evaluation, Safety and Health Assessment and Research for Prevention)