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Worker crushed following collapse of log-yarding system

Date of incident: April 2016
Notice of incident number: 2016166960010
Employers: Cable or high-lead logging company; timber-harvesting company

Incident summary
At a forestry operation, trees were being yarded using a cable yarding system. Stumps were being used to anchor three guylines necessary for stability of the yarder during operation. While a tree was being yarded upslope to a landing, the tree became hung up against a stump and a rock outcrop. A section of the stump used as an anchor for one of the guylines broke off, releasing the guyline. Then a static guyline being used as a stabilizer failed; this guyline connected the top of a spar (a pole elevating the cables) to the tracked crawler of the yarder. The spar tipped over, crushing the yarder cab. The yarder operator was inside the cab and sustained fatal injuries.

Investigation conclusions

Cause

  • Stability of spar was compromised. The stability of the spar was compromised when the tree being pulled upslope became hung up against a stump and a rock outcrop. The tension in the mainline (one of the cables) increased, which increased tensions in the skyline (another cable), the three guylines, and the back static guyline being used to stabilize the spar. One of the three guylines carried most of the additional tension, and a slab broke off the stump that this guyline was anchored to. The guyline attached to the stump released, leaving the skyline, the other two guylines, and the back static guyline to carry the increased tension. The back static guyline failed, and the spar tipped over onto the operator cab, crushing it and causing fatal injuries to the operator.

Contributing factors

  • Improper guyline setup. The guylines used to support the spar in the raised position during the yarding operation were set up in such a way as to compromise the guylines’ ability to distribute and carry the forces created during yarding operations. This positioning was not done in accordance with the specifications from the manufacturer or in a manner acceptable to WorkSafeBC.
  • Unsuitable notches in guyline anchor stump. Deep notches had been cut into the flare-rooted portion of the stump being used to anchor the guyline that released. When the tree became hung up, forces were generated that caused a slab to break free from the stump, releasing the guyline.
  • Inadequate planning. The planning for conducting the yarding activities was inadequate based on the improper guyline setup, notches in the flare-rooted stump, and insufficient lift to keep the butt end of the tree being pulled upslope clear of obstructions.
  • Lack of supervision. There was a lack of supervision at this forestry operation based on the improper guyline setup, lack of pre-use inspections of the yarder, lack of inspection of stump anchors, unsuitable notches in the anchor stumps, and failure to ensure that a tree being pulled upslope had sufficient lift to clear visible obstructions.
  • Design of spar. The design of the spar pin arrangement was such that it could not prevent the spar from rotating past 90 degrees in the direction of the operator cab, and therefore, from tipping toward the cab.

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Publication Date: May 2019 Asset type: Incident Investigation Report Summary NI number: 2016166960010