811 is a phone number, not a law. Dial it and you reach your state's one-call notification center, which forwards your dig details to the utility owners registered in that area; they mark their lines, and you keep away from the marks by hand digging inside the tolerance zone. What makes it mandatory is your state's one-call statute, backed by OSHA's own requirement that you locate before you open the ground.
Three layers of law sit behind one phone call
Crews argue about whether 811 is "an OSHA thing." It is three things at once, and knowing which layer you are in tells you who writes you up.
| Layer | What it requires | Who it binds |
|---|---|---|
| OSHA 1926.651(b) | Determine the estimated location of installations before opening the excavation; contact the owners; determine the exact location by safe means as you approach; protect, support or remove lines while the excavation is open | The employer doing the digging |
| State one-call law | The ticket itself: how far in advance, what the locator must do, ticket life, tolerance zone width, penalties | Excavators and facility owners in that state |
| 49 CFR 198.37 / 192.614 | Every state must adopt a one-call program meeting federal minimums; gas pipeline operators must mark and inspect | States and buried pipeline operators, enforced through PHMSA |
The federal floor is worth reading once. Under 49 CFR 198.37, a state one-call program must require excavators to notify the center covering the work, giving the caller's name, the excavator's name, address and phone, and the specific location, starting date and description of the work. Emergencies are the one exception: you may begin, but you must notify the center at the earliest practicable moment. Violations must carry civil penalties substantially the same as those under the pipeline safety laws.
The ticket, step by step
- White-line the dig, if the address is not enough. CGA Best Practice 5-2: when the site cannot be clearly identified on the ticket, delineate the route or area in white paint, flags or stakes, before or during the request. A single white stake with your company initials and the radius works for a site inside a 50-foot radius.
- Place the request. Phone 811 or use the state center's online portal, with the information 198.37(c) requires. Vague locations produce vague marks.
- Get the list of who was notified. Under 198.39(e), the center tells you the names of the participating operators the notice went to. That list is how you know whether a color is genuinely absent or simply late.
- Wait out the state's advance notice. Commonly two to three working days. Not a federal number — check your state center.
- Operators mark. For gas, 192.614(c)(4)-(5) requires them to tell excavators what marking to expect and how to identify it, and to mark before the work begins as far as practical.
- Verify on the ground before you dig. Compare the marks against the notified-operator list, photograph them with the ticket number visible, and write the ticket number on the permit or pre-task plan. The excavation permit generator has a field for it, and the pre-task plan keeps it in front of the crew.
What the colors mean
The APWA Uniform Color Code, keyed to ANSI Z535.1, is adopted nationwide through CGA Best Practice 4-3. States may add to it.
| Color | What is under it |
|---|---|
| White | Proposed excavation |
| Pink | Temporary survey markings |
| Red | Electric power lines, cables, conduit and lighting cables |
| Yellow | Gas, oil, steam, petroleum or gaseous materials |
| Orange | Communication, alarm or signal lines, cables or conduit |
| Blue | Potable water |
| Purple | Reclaimed water, irrigation and slurry lines |
| Green | Sewers and drain lines |
A missing color is a question, not a clearance. If the notified-operator list includes a gas utility and there is no yellow paint on the ground, somebody has to answer why before the machine starts.
The tolerance zone: 18 inches, and hands only
Marks are an estimate of position, not a survey. CGA Best Practice 5-19 defines the tolerance zone as the width of the facility plus 18 inches on either side of its outside edge, and states are free to require more. A 12-inch main therefore owns a 4-foot band of ground.
Inside that band, OSHA takes over: 1926.651(b)(3) says that when excavation approaches the estimated location of an installation, the exact location shall be determined by safe and acceptable means. In practice that is hand digging, air or vacuum excavation, or a probe — never a toothed bucket. And once you have exposed the line, (b)(4) requires it to be protected, supported or removed as necessary while the excavation stays open.
What the ticket does not cover
- Private lines. The center reaches its members. Site lighting, propane, irrigation, septic fields, the feed to a shop, a sign or a gate: nobody marks those unless the owner hires a private locator. OSHA still holds you to 1926.651(b)(1) for anything reasonably expected to be encountered.
- Abandoned and unrecorded facilities. Old services that were cut and left, a line replaced on a new alignment, work done before records were kept. Pink paint may mean "unknown facility" on some jobs — treat it as live.
- Depth. A locate marks horizontal position. It does not promise depth, and nothing in Subpart P lets you assume one.
- Anything after the ticket expires. Ticket life and renewal are state law. When the marks are gone, so is the locate.
- The soil. A clean locate says nothing about cave-in protection. That is a separate decision under 1926.652 — see sloping vs shoring vs shielding — and it needs the trench slope numbers before anyone climbs in.
If you hit something anyway
The Common Ground Alliance's 2024 DIRT Report analyzed 196,977 unique damage reports to buried utilities in the United States. Damage is not rare, and what happens in the first minute decides whether it stays a repair bill.
- Stop work. Leave the machine where it is if moving it could worsen the contact, and shut down ignition sources if gas is involved.
- Get everyone out of the excavation and upwind, then call 911 and the facility owner from a distance.
- Do not pinch, plug, cap, tape or backfill over a damaged line, and do not attempt a repair.
- Report the nicks too. Coating damage that nobody logs is what fails months later, and 192.614(c)(6) exists because operators are required to inspect lines they believe may have been damaged.
- Write it up the same day: ticket number, marks present, depth found, equipment in use. That record is your defense and your lesson.
Run the crew through it before the shift rather than after: the Call 811 Before You Dig toolbox talk is a printable 10-minute version of this page.
Bottom line
- 811 reaches your state's one-call center. The obligation is state law plus OSHA 1926.651(b); the federal floor for the system is 49 CFR 198.37.
- Ask the center which operators were notified — that list turns a missing color into a question you can answer.
- Tolerance zone: facility width plus 18 inches each side, hand or vacuum excavation only, per CGA 5-19 and 1926.651(b)(3).
- Private lines, depth and abandoned facilities are outside the ticket. They are still inside your obligation.
- Photograph the marks with the ticket number, and re-notify when the ticket expires or the marks are gone.