The tolerance zone is a safety area that spans the width of a marked underground utility plus a specified distance from each indicated outside edge of the utility. This specified distance varies from state to state. It is 18 inches in Kentucky and Ohio; 24 inches in Indiana; 30 inches in North Carolina; and 24 inches in South Carolina.
Some states require you to first hand dig to expose the facility and visually verify the precise location of all marked utilities before power digging or using mechanized equipment in the tolerance zone. Other states do not allow any mechanized equipment or power digging within the tolerance zone; only hand digging or other non-intrusive methods are permitted. It is the excavator’s responsibility to know and follow the requirements in each state.
When digging in the tolerance zone, use reasonable care and these nondestructive digging methods:
- Hand digging with a blunt shovel. Never use a pickaxe or pointed spade, and never stomp on a shovel with both feet. That’s a sure way to damage a utility line. Instead, use a blunt shovel to loosen soil, working at an angle.
- Vacuum excavation. This method uses suction and water to quickly and safely remove soil. Be mindful of water pressure; use lower pressure and tips with multiple nozzles.
Once you have exposed buried utilities, proceed with extreme caution. Power digging equipment can damage a section of electrical conduit or pipeline in no time. Even hand digging can compromise buried utilities by removing supporting soil. Take all necessary precautions to protect buried utilities from damage.
Additional digging guidelines, case studies, instructional videos, and training tools can all be found, at no charge to you, on Duke Energy’s e-SMARTworkers™ website.
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