“The Tolerance Zone.” It might sound like The Twilight Zone, a classic TV series hosted by Rod Serling, or The Phantom Zone, an interdimensional prison seen in Superman comic books.
Actually, it’s neither.
The Tolerance Zone shows up once you’ve made the free call to 811 to get underground utilities flagged in your work area. When those small multi-colored flags are in the ground, or painted marks are on the ground, the Tolerance Zone appears as if by magic. Well, ok, you have to imagine it, but it’s there.
The Tolerance Zone refers to the amount of space parallel and directly next to the underground utility.
Here’s a diagram.
In the state of Texas, and in this diagram, the Tolerance Zone is half the nominal diameter of the underground pipeline plus a minimum of 18 inches on either side of the outside edge of the underground pipeline on a horizontal plane.
The Tolerance Zone is there as an added protection to buried utilities.
Digging methods to consider in the Tolerance Zone other than careful hand digging include pot holing, soft digging and vacuum excavation methods. Of course, if you have to break through pavement or concrete, these non-invasive methods are not required until after the hard shell is off.
No matter how you uncover what’s below, ALWAYS verify the location of a buried utility by sight before using ANY power or mechanical equipment within the Tolerance Zone.
Until next week, safe digging!