Tolerance Zone

Safe Digging: Digging inside the Tolerance Zone - Potholing

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Safely exposing an underground facility is the best way to work within the tolerance zone. That way you know precisely where the underground facility is located, making it easier to avoid.

Before you can use mechanized digging equipment in a tolerance zone, you must verify the presence and location of the buried facility. There are many non-destructive methods to expose underground facilities including hand digging, vacuum excavation, pot holing and soft digging. If you must remove pavement or masonry, equipment can be used, but only to the depth of that pavement or masonry.

If you are unable to locate the facility after performing a reasonable search, contact the facility owner directly for help. Once the facility is located, mechanized digging equipment can be used.

If you will be exposing a facility during your excavation, you are required to provide adequate support and protection for it. An unsupported portion of a line can pull and distort a joint or splice that is out of sight. The damage can occur several feet up the line - underground - and you'd never see it.In addition, you are required to provide an adequate backfill upon completion. 

Safe Digging: Sticky Tolerance Zones

Sometimes tolerance zones can be tricky. In the example below a hospital is adding a drop-off area to the front of the building (indicated by the purple box). It is located in a major intersection with many underground facilities.

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Here, the facility locators have marked the communications and electric lines. The gray area represents your work site, which you have white lined. What you notice is the communications (orange) line runs through your work site and the electric line is outside your worksite. 

Here, the facility locators have marked the communications and electric lines. The gray area represents your work site, which you have white lined. What you notice is the communications (orange) line runs through your work site and the electric line is outside your worksite. 


The entire tolerance zone for the communications line is within your work site. Remember, the tolerance zone is 24 inches on either side of the underground facility. Because the electric line is outside your work site, can you assume that beyond the communications line you can dig freely?

The entire tolerance zone for the communications line is within your work site. Remember, the tolerance zone is 24 inches on either side of the underground facility. Because the electric line is outside your work site, can you assume that beyond the communications line you can dig freely?


NO! When you figure the tolerance zone for the electric line, you see that it runs within your work site. If you dig beyond the communication's tolerance zone without first verifying where the electric line runs, you run the risk of damaging the electric line.

NO! When you figure the tolerance zone for the electric line, you see that it runs within your work site. If you dig beyond the communication's tolerance zone without first verifying where the electric line runs, you run the risk of damaging the electric line.

Safe Digging: Measuring the Tolerance Zone

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Every underground facility has a tolerance zone. The tolerance zone helps protect facilities from damage. It offers a margin of error for those times when the underground facility is not directly underneath the locate marks.

In Florida, the tolerance zone for an underground facility is the width of the line, cable or pipe plus 24 inches on either side.