Missoula Electric Coop Jib Failure Incident January 10, 2013

Missoula Electric Cooperative Incident Investigation Report Name of person reporting incident: Mitch Dupree Person reported to: Bart Peterson Witness: Greg Scott, Cliff Bergeson, Scott Burton Date: January 10, 2013 Time: 11:00am Location: Little Ovando Substation Nature of Incident: Jib failure Description Description of how the incident occurred: The crew was re-hanging the top switch of a 3-way 69Kv loadbreak structure. The Switch was suspended and bolts removed in order to insert brackets and longer bolts that were not installed on the initial set. Switch make was a Secco Type 3 GL (CAT#3G06906SN) The crew was using the line truck (Altec D3060 TR) with a 6’ jib extension (3" round Chance). Due to the need to maintain clearance from the boom to the switch the line truck set up further from the structure than normal and full boom extension was used with the jib extension set an angle more horizontal than vertical from the boom. After an extended period of time estimated at 15 min the extension failed at the point of attachment to the boom and barber chaired. This resulted in the top switch assembly dropping down onto the middle switch damaging one vacuum bottle assembly on the middle switch. The crew secured the switch, lowered the boom and replaced the failed 6' extension with 3' Jib extension adjusted truck and jib for a more vertical angle to complete work. The top switch installation was completed and the middle vacuum bottle removed for repair. Damages Damages include: Broken Chance 6' auxiliary mast arm, Two broken welds on center vacuum interrupter requiring repair.

Analysis Acts or conditions contributing to the incident: (1) The switch was heavier than anticipated. The crew estimated the weight to be approximately 450lbs. Using weights from Seeco publications the section of switch weighed approximately 1000lbs. No weights for the various components of the switch were provided from the factory with the switch. (2) There were no load rating charts available for the jib extension assemblies. The Chance technical support advised that the 6' length, 3" diameter Chance Auxiliary Mast Arm was not designed for material handling. It is rated for the lifting of conductors with a maximum transverse load at the wire holders of 450lbs total. Unknowingly, the crews have been using the Auxiliary Mast Arm for the wrong application as a material handler. It had been used in the same capacity for many years without incident. There is the possibility that the jibs structural strength may have been compromised over the years of improper use. (3) The design of the switch requires the boom angles to be lower than usual to provide clearance between the boom and the switch body. (4) Without clear cut procedures for incident reporting and investigation the crews may have placed themselves in additional risk by not stopping work and having incident investigated to determine that potential hazards of using a similar shorter jib to complete the work. Root Cause Insufficient information provided to crews in several areas: Proper use and application of jib extensions No load charts/data on jib extensions Weights not provided or measured for switch

Steps to Achieve Recommended Permanent Solution Job re-training: Review the proper application of material handling and wire handling equipment. Review the importance of knowing your lifting weight and rigging appropriately. Job method change: Use appropriate material handling boom extension within it's rated capacity when required. Ensure that lifting weights are available at the time of lift for non-standard equipment. If no published weights are provided a dynamometer shall be used to determine weight before lifting. If the ability of MEC equipment to safely perform a lift is in question a properly sized crane will be contracted to complete the lift. New incident reporting/investigating procedures to be created and implemented to provide employees with an uniform and structured process for the reporting and investigation of incidents. Engineering change: Engineering shall provide manufacturer's published weights for nonstandard equipment with the work order whenever possible. Completed and reviewed by MEC Accident Investigation Team Sean Eskridge __________________ Date:______ Seth Hill __________________ Steve Douglass __________________ Reviewed by Safety Committee Date:______