This short presentation describes a preventable workplace incident where a worker in Washington state was killed on the job and is narrated by the L & I safety inspector who conducted the investigation. To view the narration script, click on the button on the lower right corner of the screen. To move between slides, or view a particular slide again, click on the same lower right hand corner button and then click on the back and forward arrows at the bottom of the screen.
Hello, my name is Monte Hanks, and I am a compliance safety and health inspector with the Dept of Labor & Industries, Division of Occupational Safety & Health. In August 2010 I investigated a workplace fatality at a remote logging site. A 47 year-old worker was fatally injured while operating a mechanical timber harvester with an attached saw bar and chain cutting head.
The operator was thinning trees with a mechanical cutting head similar to the one in this photo when a “chain shot” occurred. In mechanized timber harvesting, a “chain shot” is a serious hazard. A chain shot is the high velocity separation and ejection of a piece or pieces of cutting chain after the chain suddenly breaks. This exposes both machine operators and bystanders to risk of serious injury or death. This typically occurs near the drive end of the cutting system but can also come from the tip area of the bar. The small ejected links of chain can travel at speeds over 750 miles per hour.
In this situation, the mechanical harvester was cutting the tree into sections when the chain broke. A piece of chain link separated from the chain and flew at the cab at high speed. The chain link penetrated the polycarbonate side entry window striking the operator in the neck, fatally injuring him, as shown in this animation of the incident.
The photo on the left shows the chain piece that flew off hitting the side window. The photo on the right shows the cab window where it was penetrated by the broken link. The Lexan window of the cab is made up of ˝ inch thick polycarbonate which is sometimes called bullet-proof. However the piece of chain that penetrated the window was traveling as fast as a bullet and broke through this barrier. During the investigation of this tragic accident we discovered that it was both the logging industry's and harvester manufacturer's assumption that the cab 's half–inch thick polycarbonate plastic window provided adequate protection from outside hazards including a chain shot. There was no citation issued from this incident, but a hazard alert has since been published.
After a chain break, the free end of the chain begins to whip away from the break 2. 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.
3. At the peak of the whip, chain parts may break loose and be ejected at super sonic speed. It is important to know that a sudden release can happen from the tip or rear end of the bar. 4. A chain shot can cause parts to be thrown in many directions, especially those along the plane of the saw bar.
Mechanical harvester cutting heads should be equipped with a chain shot guard. Broken chains must be repaired properly using the proper spinner tool and avoid hammered rivets or used parts. Do not repair if the chain has been broken more than once. Replace it.
When possible, position the saw head so that a breaking chain is not in direct line with the cab or nearby workers. Close all snow holes on processor heads, inspect the chain on a regular basis looking for cracks, worn parts and bad rivets; use the right type and amount of lubricant on the chain, and finally, don't pump up or boost chain speed beyond the manufacturers recommendations. Please note that the manual for the chain and bar need to be reviewed in addition to the machine manual. It provides more specific instruction for maintenance and use of the saw than the manual for the harvester itself.
We want to make sure all of you working in the woods go home alive and without injuries each day. Follow these recommendations to avoid a “chain shot” event at your worksite and help us keep Washington safe and working.