Underground Utilities and 811: Locating, Exposing and Protecting Lines

Every excavation starts with the same question: what is already in the ground? Gas, electric, telecom, water and sewer lines can be anywhere, and records are often wrong. OSHA and every state's damage prevention law require excavators to find out before the first bucket goes in.

What OSHA requires

1926.651(b) sets four requirements:

1. Determine the estimated location of sewer, telephone, fuel, electric, water and other underground installations before opening an excavation.
2. Contact utility companies or owners within established or customary local response times, tell them about the proposed work, and ask them to establish the location of their installations before excavation starts. If they can't respond within 24 hours (unless state or local law sets a longer period) or can't establish the exact location, the employer may proceed with caution using detection equipment or other acceptable means to locate the utility.
3. When excavation approaches the estimated location, determine the exact location by safe and acceptable means.
4. While the excavation is open, protect, support or remove underground installations as needed to protect employees.

How the 811 process works

811 is the free national phone number that connects excavators to their state's one-call center (most also take online tickets). The details are set by state law, but the process usually looks like this:

1. White line the proposed excavation area with white paint, flags or stakes, where the state requires or recommends it.
2. Submit a locate request to 811 a set number of business days before digging. Two to three full working days is common, but check your state.
3. The one-call center notifies member utilities, who send locators to mark their lines.
4. Wait for all responses. Many states use a positive response system that tells you whether each utility has marked or cleared.
5. Respect the marks and the tolerance zone, and keep the ticket current. Tickets expire, and marks must be refreshed if they fade or the work continues past the ticket life.

Reading the paint: APWA uniform color code

Marks often include the operator's initials and sometimes the size or material of the line.

The tolerance zone

The marks show an approximate location, not the exact one. State laws define a tolerance zone on either side of the outside edges of the line, commonly 18 to 24 inches. Inside the tolerance zone:

• Use hand tools or vacuum excavation (soft digging) to locate the line. Don't use powered equipment.
• Pothole to expose the line and confirm its depth and direction before excavating near it.
• Once a line is exposed, support and protect it. Long exposed spans, especially cast iron or plastic, can sag and break.

When something goes wrong

If you hit or damage a line, even a scrape on a coating:

• Stop work. Don't try to repair, crimp or bury the damage.
• Gas leak: evacuate everyone upwind, eliminate ignition sources (shut off equipment if safe), keep people away, and call 911 and the gas company from a safe distance.
• Electrical contact: stay on the equipment if it's safe to do so, warn others to keep away, and call 911 and the power company.
• Report the damage to the facility owner and through 811 as your state requires, even if it looks minor. A nicked coating can fail weeks later.
• Treat the trench as a changed condition. A water main break can wash out soil behind a shield or under shoring.

Key takeaways

• OSHA requires you to estimate utility locations, notify owners, find the exact location as you approach, and protect exposed lines.
• Call or click 811 before digging and wait for every utility to respond.
• Red electric, orange communications, yellow gas, green sewer, blue water, purple reclaimed, pink survey, white proposed excavation.
• Hand dig or vacuum excavate inside the tolerance zone, and pothole before mechanical digging nearby.
• After a strike: stop, evacuate if needed, call 911 and the owner, and report it.

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1926 Subpart P. It does not replace the site-specific training and competent person your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.