How to Avoid Underground Utilities During Directional Drilling

Underground utility lines must be installed safely and appropriately. However, horizontal drilling poses unique challenges due to significantly more limited visibility than vertical drilling. However, it is possible to limit risks by utilizing the most effective horizontal directional drilling (HDD) equipment and ensuring high-quality training. Safety is best ensured by avoiding contact with existing utility lines, including electrical, sewage, gas, water, chemical, and steam. Not only can incorrect drilling pose costly risks to equipment, but it can be dangerous to the operator and others nearby. For example, if the drill comes into contact with underground electrical wires, there is a risk of electrocution, whereas a strike to a natural gas line could result in a gas leak or potential explosion. Reading and understanding the following information will help ensure that drilling is completed efficiently, effectively, and safely.

While HDD is considered a trenchless technique, sometimes trenches must be dug out to accommodate machinery or a reception pit. To guard against cave-ins at trench sites, it is essential that trench/excavation controls are effectively implemented in accordance with (29 CFRE Part 1926 Subpart P).

To avoid potential crush injuries due to unexpected movements of machinery, workers must never be present in the area between a machine and a trench wall when the drilling machine is moving down a ramp towards a hole.

There have been several occurrences of fires and explosions in connection with HDD. Often, these could have been prevented if the appropriate safety measures had been taken. For example, an HDD operation that aimed to install underground cable in Kansas City, MO., had an accident that led to disaster in 2013. The workers at the site relied on hand-dug “potholes” along the anticipated path of the drill for guidance, revealing two utility lines approximately two feet underground. Upon this discovery, they assumed one of these lines was the gas line they were looking to avoid striking, even though it was not quite as deep as they had anticipated. They did not take the additional measure of verifying this assumption, and as it turned out, both of these lines were electrical, and the gas line was set deeper. They continued working, drilling deeper to lay the path for the new cable—until they struck the gas line, causing an explosion and fire injuring three HDD workers, destroying a restaurant, and causing significant damage to nearby structures. Tragically, several bystanders were injured, and an employee of the aforementioned restaurant was killed.

How to Avoid Underground Utility Lines

When using HDD, it is imperative that underground lines are verified using surface markings before drilling begins. It is vital when performing both vertical and horizontal drilling. However, identifying underground lines may not always be straightforward as they may be undocumented, covered by other lines, placed at depths that do not coincide with code requirements, or have shifted to a different position due to settling. It is vital to rely upon several verification methods before beginning the drilling process.  

Best Practices for Verifying and Avoiding Underground Utility Lines

• A visual inspection of the planned digging path should be performed to account for structures that could indicate potential underground utility lines, including gas meters, manhole covers, etc.
• A thorough review of drawings of the area should be conducted, followed by direct contact with utility companies to verify the location of possible underground utility lines.
• Always compare findings from the above preliminary steps with surface markings to identify any potentially missed utilities.

Utilize “potholing” and other safety precautions to ensure no existing utility lines are in the drill's path. Call 811, the “Call Before You Dig” number, can be helpful in more firmly establishing the location of any underground utility installations within the work site.

Potholing: Dig to Verify Utility Lines

It is best to physically confirm the location of underground utility lines with a process of “potholing” along the projected drill path. By hand-digging vertical holes (or using a vacuum excavator), workers can visually observe the projected path for line locations. With potholing, the potholes must be dug to the depth of the planned drill path, even if it is deeper than the deepest expected utility line, to identify lines that may be hidden or undocumented.

Potholing is also an effective tool for monitoring drilling equipment during the drilling process. Potholes enable the tracker to utilize a tracking device to ensure the equipment follows the planned path and to witness the drill stem and head during the drilling process, offering another safeguard to help the machine operator avoid utility strikes. The tracker’s role is to warn the HDD operator of the presence of utility lines or other obstacles in enough time to implement a directional change if necessary.

Implementing Safety Precautions to Avoid Underground Utilities

The risk of contacting underground utilities is dramatically reduced by implementing adequate safety precautions and safe work practices unique to each worksite from start to finish. It is vital to conduct site-specific safety assessments, develop and implement site-specific work plans, ensure all project workers are appropriately trained, and ensure the correct usage of equipment—including personal protective equipment (PPE) under (29 CFR Part 1926 Subpart E).

All HDD workers and management should be aware of the potential hazards associated with HDD operations, including being struck by or caught on mechanical equipment with rotating parts, risks from high-pressure drilling fluid, and the danger of coming into contact with electric, gas, and other underground utility lines.

These safety precautions can help ensure a safe worksite:

• Always rely upon site-specific information. For example, site-specific safety assessments should be performed to determine the best drilling technique and safety practices for the particular job (i.e., when potholing, drilling the bore, or using a back reamer).
• Be sure to reach out to the local utility location service to have lines marked and
• Contact the local utility location service to mark lines and provide information about the location of existing utility installations. Even after receiving this information, it is important to compare drawings to these surface markings to ensure all lines—even those missing from utility maps—are on the project’s radar.
• Carefully review drawings and reach out to utility companies to confirm the location of underground utilities.
• Require that the HDD machine operator and the tracker perform a site walk along the projected drill path during the project's planning and site preparation phase. It is important to check for structures, such as gas meters and manhole covers, that could indicate an existing underground utility line, obstruction, or other sources of interference to the drill or tracking device readings.
• Rely upon potholing techniques that are safe and effective to expose potential underground utilities along the projected drill path.
• Ensure that all HDD machine operators and trackers are well trained before the operation begins. In particular, they should be able to communicate effectively using hand signals and radios.
• Trackers should also be taught to check transmitter readings often throughout the HDD operation and to compare them with readings obtained during the pre-operational walkthrough. Should they note any changes in readings, such as discrepancies in depth, the tracker should signal the HDD operator to stop the drilling process to investigate. Appropriate safety measures should be taken before the drilling begins again.
• Trackers must be instructed to observe the potholes for the o drill stem as it passes near utility lines, then guide the HDD operator to drill along the bore path to avoid striking lines.
• Drilling should be performed slowly to allow the tracking device to maintain its ability to sense large obstructions in time to pause drilling and redirect.
• Drilling projects must comply with applicable local, state, and federal regulations from start to finish, including OSHA, Department of Transportation (DOT)—particularly Pipeline and Hazardous Materials Safety Administration—Federal Aviation Administration (FAA), Federal Highway Administration (FHWA), Federal Railroad Administration (FRA), and others.

Natural Gas Line Strikes: Risk of Explosion and Fire

As indicated previously, a strike to natural gas line can dramatically impact the work area and the area surrounding the worksite, including an explosion and fire hazard. All workers should be aware of the ramifications of the drill stem, head, or back reamer striking a natural gas line, including the possibility of leaking gas into the workspace or causing a build-up of trapped air that could result in an explosion due to the explosive nature of natural gas.

Natural gas is highly flammable and easily ignited by everyday activities, including the presence of an open flame, static electricity, diesel engine glow plugs, or sparks from HSS machinery or equipment. As it builds up in a space, there is an increased risk of explosion and fire. This underscores the importance of verifying natural gas lines and all utilities through safe and effective potholing techniques. This simple act that allows the tracker to better guide the HDD operator could prevent a tragedy that could result in injuries and fatalities to workers and others nearby.  

Preventing Natural Gas Explosions and Fires as an Employer

Employers have a crucial role to play in preventing natural gas explosions and fires in the HDD industry. All employers should develop a carefully constructed fire protection program and ensure workers follow it through all phases of construction—including HDD operations (29 CFR 1926 Subpart F). Additionally, employers have the responsibility of prohibiting any open flames or smoking at a worksite where HDD operations are occurring (29 CFR 1926.151(a)(3).

It is essential to prepare an appropriate site-specific Emergency Action Plan (EAP) that workers are expected to follow should any emergency occur. This should include potential emergencies like gas, electric, or sewer line strikes, and it should be effectively communicated to anyone who will work at the particular site in any capacity in accordance with OSHA requirements for EAPs in construction (29 CFR 1926.35(e)(2). This document should include the potential steps to be taken in the event of a natural gas leak—or a suspected gas leak—including evacuating staff and those nearby to a safe location, calling 911, and reaching out to the utility company immediately. It is critical that anyone using a cell phone to make these calls move away from any area where natural gas could be present beforehand.

It is the employer's responsibility to train all workers about appropriate actions to take as precautions to avoid such situations and how to respond during different types of emergencies. All workers should be immediately alerted and evacuated to a safe, predesignated assembly area in an emergency.

Identifying a Natural Gas Leak

All workers should be able to identify natural gas leaks. There are several ways to do this, which include:

• Utilizing handheld natural gas detectors—the most effective method.
• Monitoring the site for dirt, water, or debris blowing from the ground into the air.
• Hearing an unexpected hissing, whistling, or roaring sound near a natural gas line.
• Smelling a sulfur-like odor due to the element added to some natural gas. However, not all gas is odorized, nor can everyone smell the scent. Therefore, it should not be an expectation that any unusual smell will be noticed during a gas leak event.