Damage Prevention Starts with You

Always verify underground lines, using surface markings, before drilling 
vertically or horizontally to avoid hitting them. Since underground lines can 
be difficult to identify if they are covered by other lines, are undocumented, 
are buried at depths different from code requirements, or are in a different 
position from initial installation due to ground settling, it is important to use 
multiple identification and verification methods before drilling.

To verify and avoid underground utility lines when using HDD:

• Visually inspect the entire planned digging path for structures that 
  indicate potential underground utilities (e.g., gas meters and 
  manhole covers).
• Review drawings and contact utility companies directly, whenever 
  possible, to verify underground utility locations.
• Compare findings with surface markings (discussed below) to 
  identify any missed utility.
• Employ potholing and other safety precautions described below to 
  further identify and avoid lines in the drill path.

One common industry practice is to call 811, the "Call Before You Dig" number, to establish the location of the of any underground utility installations in the work area.

---

The risk of striking underground natural gas or electric utility lines increases when HDD is used in urban areas.

---

Underground service locators typically cannot provide depth information for utility lines. Employers must implement safe work practices that always verify the depth of utility lines near the planned drill path to prevent hitting them.

If possible, physically verify underground utility line locations by potholing along the planned drill path. Potholes are vertical holes dug by hand or with a vacuum excavator. It is important that potholes go to the planned drill path's depth—even if this is beyond the deepest known utility line—to identify any hidden lines. Potholing also allows the tracker to visually observe the drill stem and drill head during drilling to ensure that the HDD machine operator avoids striking utility lines along the drill path. The tracker typically uses a tracking device to determine whether the drill stem and head are following the planned drill path. The tracker is there to warn the HDD machine operator about utility lines with enough time to change direction if needed.

---

Verify underground utility lines visually by potholing. This allows the tracker to guide the HDD machine operator to maneuver the drill stem to avoid striking utility lines and prevent an incident that could result in worker injuries or fatalities

Conduct site-specific safety assessments, develop and implement site-specific work plans, train workers, and provide and ensure the use of the right equipment to workers, including personal protective equipment (29 CFR Part 1926 Subpart E). Ensure the use of safe work practices from the planning phase to completion. Potential hazards associated with HDD operations include mechanical rotating parts (e.g., struck-by, caught-in), high-pressure drilling fluid, and damaging electric and gas lines and other underground utilities (e.g., electrocution, fires, explosions). Take the following safety precautions:

• Use site-specific safety assessments to determine appropriate drilling techniques and safety practices (e.g., when potholing, drilling the bore, or using a back reamer).
• Contact the local utility location service to mark lines and assist with determining utility locations. Compare drawings with surface markings, as some utility lines may miss detection or may be missing from utilities maps.
• Review drawings and contact utility companies directly, whenever possible, to verify underground utility locations. 
• Ensure that the HDD machine operator and tracker walk through the planned drill path during planning and site preparation. Check for structures (e.g., gas meters and manhole covers) that may indicate an underground utility line, obstructions along the drill path, and potential sources of interference that could affect tracking device readings.
• Use safe and appropriate potholing techniques to the planned drill path's depth to expose any hidden underground utilities.
• Train HDD machine operators and trackers before starting the operation to communicate effectively with hand signals and radios.
• Ensure trackers check the tracking device readings frequently during HDD operations and compare them with the pre-operational walkthrough readings. If any changes in readings occur (e.g., depth), the tracker should immediately signal the HDD machine operator to stop drilling, investigate, and take appropriate safety precautions before continuing to drill.
• Instruct trackers to look into the potholes to observe the: 
  - drill stem as it passes near underground utility lines during drilling, and guide the HDD machine  operator along the bore path to avoid striking a line;
  - back reamer to verify that it follows the bore path and avoids utility lines.
• Drill at a pace that is slow enough to permit the tracking device to sense any drill line deflections caused by large obstructions.

Comply with all applicable local, state, and federal regulations, including those issued by OSHA, Department of Transportation (DOT) (e.g., Pipeline and Hazardous Materials Safety Administration), Federal Aviation Administration (FAA), Federal Highway Administration (FHWA),Federal Railroad Administration (FRA), and others.

Striking underground natural gas lines may present explosion and fire hazards in the workplace and surrounding areas. If the drill stem, drill head, or back reamer strikes a natural gas line, gas may leak into the workspace, or build up where air can get trapped in the area (e.g., buildings, vaults, pits), and result in an explosion and fire. Natural gas is easily ignited by an open flame, static electricity, glow plugs from diesel engines, or sparks from the HDD machine or nearby equipment. As natural gas accumulates in a space, higher concentrations increase the risk for an explosion and fire.

Employers must develop a fire protection program and follow it throughout all construction phases, including HDD operations (29 CFR Part 1926 Subpart F). Employers must prohibit open flames and smoking at a worksite when conducting HDD operations (29 CFR 1926.151(a)(3)). Develop and implement an adequate site-specific Emergency Action Plan (EAP) for workers to follow for different emergencies that could occur—such as gas, electric, or sewer line strikes—and communicate the plan to all workers (see 29 CFR 1926.35(e)(2) for OSHA requirements related to EAPs in construction). Include steps in the EAP to take if a natural gas leak is suspected, including immediately evacuating the area and, from a safe location, calling 911, and the utility company. If using a cell phone, move away from the area where there might be gas before calling. Employers need to train all workers on appropriate precautions to take during different emergencies, immediately alert all workers in an emergency, and evacuate workers from unsafe areas to a safe, predesignated assembly location.

Employers must ensure that workers can identify a potential natural gas leak. Handheld natural gas detectors are most effective, but other indicators include:

• Dirt, water, or debris blowing from the ground into the air.
• An unusual sound, such as hissing, whistling, or roaring, near a natural gas line.
• Smelling a distinctive sulfur-like odor, which is typically added to natural gas, although some people cannot smell the odor. Note that not all gas is odorized, especially at large industrial sites, and may be impossible to smell.

---

Immediately contact local emergency responders (e.g., call 911) if excavation damage results in a natural gas release. See OSHA SHIB Hazards Associated with Striking Underground Gas Lines