Jack Hammering of Electrical Conduit Incident Root Cause Analysis Final Report

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1 Root Cause Analysis Final Report Department: O&M Incident Date: Jobsite: Sun Valley Mall just outside of Lucille s Smokehouse BBQ Nature/Severity: No injury; Damage to 480 V electrical power line Incident Summary: A crew was in the process of installing two new service lines, meters and a backflow device for a restaurant. Based on design drawings produced by Engineering all known utilities had been located through the USA process and some design changes had already been discussed with the Design Engineer due to actual field conditions. After installation of the new lines and the completion of cut-overs, the existing service lines were to be abandoned. Design drawings provided by Engineering indicated a 21 KV duct bank would transverse the trench. This duct bank was located during trenching without incident. However, a private 4 electrical conduit that ran parallel with trench was not shown in the Engineering drawings. The applicant provided the background survey and utility data to assist in design development. However, Engineering did not cross check the utility record information directly from Sun Valley Mall staff. Later, Sun Valley Mall staff provided O&M a drawing indicating a private electrical conduit was also present in the trench area but their drawing was imprecise and the electrical conduit s depth was not provided. The private 4 electrical conduit was not marked in the USA process so CCWD s locators were called in to assist in marking it. Based on information from Mall staff, CCWD locators identified an electrical line running parallel at the location where the crew was planning to trench. The electrical marking was within two or three inches of the actual 4 electrical conduit location. The crew decided to trench at the location of the marked electrical line because other existing utility conflicts indicated on the drawings and located in the field, precluded them from working around the marking. The crew was able to safely expose the 4 electrical conduit in the beginning of the trench at a depth of two feet. Later in the trench work, a crew member was jack hammering the sidewalk near the electrical conduit markings when an electrical contractor from inside Lucille s BBQ informed the crew that a loud arc blast occurred at electrical equipment located in the basement. The jack hammer had struck a 480 V electrical line that was encased in the concrete sidewalk just 10 inches from the surface causing the power to go out at the nearby Firestone business. The crew member did not sense an electrical shock and was not injured in any way. He was wearing safety boots and leather gloves. The 4 electrical conduit was encased in the sidewalk concrete and not visible when the incident occurred. The electrical power was turned off and locked out by Mall staff prior to fully exposing the broken conduit. The crew carefully chipped the concrete to expose the conduit without further damage.

2 Page 2 of 5 View of the site just after a 480 V conduit was struck by a jack hammer. The conduit is not visible. 480 V conduit was encased in concrete 10 inches below the sidewalk surface. Note the conduit s locating mark between the feet of the worker. At the lower right, an unmarked 4 communication conduit was safely exposed though just inches below the pavement section. The 4 conduit was later identified as AT&T who had failed to mark it during USA clearence.

3 Page 3 of 5 Section of punctured metal electrical conduit along with jack hammer gad with burned point. Note the two private electrical conduits are not encased and very shallow to clear an old concrete wall.

4 Page 4 of V conduit after repair made.

5 Page 5 of 5 Contributing Factor(s): Though the 480 V electrical conduit was located and marked, it was at a shallower depth than the crew expected and encased in non-red-colored concrete (along with the sidewalk). There was not enough room to excavate while avoiding all utility conflicts. Root Cause (s): The Excavation SOP does not cover the safe removal of pavement within 24 inches of electrical markings. The procedures do not include the required use of electricallyrated PPE such as insulated boots, gloves or mats. Corrective Action Plan: Revise the Excavation SOP to include a request for the deenergization and lockout-tagout of electrical lines suspected of being less than two feet from the surface prior to powered pavement removal. If the electrical line cannot be deenergized or cannot be positively identified but known to be present in the vicinity, use insulating mats, gloves and boots rated for the hazard. As an additional precaution, ground the jack hammer where a proper ground is available. Update the Excavation Awareness training program to include changes to the Excavation SOP and to instruct employees not to assume depths of utilities to remain constant, and where possible, fully expose utilities to identify alignment by soft-digging before proceeding to power excavate, jack hammer or saw cut. Although not a factor in this incident, update Engineering Standard Practices to ensure all survey information is obtained and cross checked, where feasible, as part of the design development. Person Responsible: Pete Schoemann Spiro Zapantis Due Date: 6/15/13 Spiro Zapantis 6/15/13 Rachel Murphy 8/15/13