My State:
May 07, 2018
Recognizing the hazards of trenchless drilling

One of OSHA’s priority goals for 2018 is the reduction of worker injuries from excavation and trenching accidents. The goal emerged from a troubling upswing in trenching fatalities over the past 7 years. One approach to the problem is horizontal directional drilling (HDD), also called trenchless drilling. This technology eliminates the hazards of open trenches, mainly cave-ins or collapses of the trench walls. HDD is expected to piggyback with the growth of telecommunication and natural gas distribution, particularly in urban areas where traditional trenching can be highly disruptive.

But HDD comes with its own set of hazards, at least one of which places more people at risk than trench cave-ins. OSHA, the Department of Transportation, and standards organizations such as ASTM International have promoted basic safety procedures that reduce the risk of injuries to workers and others at HDD sites. OSHA recently reviewed the fundamentals of these procedures in a Safety and Health Information Bulletin (

What is it?

HDD uses surface-launched equipment to drill underground horizontally and install pipes, conduits, and cables.  The process comprises three fundamental steps:

  • Drill the pilot bore. The HDD machine operator makes a pilot bore by running the drill stem and head through the entire drill path, from the entry point to the exit point in the reception pit. A worker called a tracker uses a handheld tracking device and potholes to ensure that the operator is drilling along the predetermined path and avoiding underground utility lines. Drilling fluid is pumped through the drill head to reduce friction, make the bore stable, and remove cuttings. Workers may change or add drill rods to extend the drill stem, as needed.
  • Enlarge the bore. Once the pilot bore reaches the reception pit, the drill head is removed, and a back reamer is attached to the drill stem. HDD machine operators pull the back reamer from the exit point through the pilot bore to the entry point, making the bore hole larger.
  • Install conduit/casing. Concurrent with the bore-enlarging operation, conduit or casing (i.e., product pipe) is attached to the back reamer and pulled into the bore until arrives at the entry point, where the drill stem and back reamer are removed. During the entire operation, the tracker continues to monitor with the handheld device and the potholes to ensure that no utilities or obstacles are hit.


Although HDD technology takes less time, requires fewer workers, and causes less surface damage compared to traditional open trench excavations, it is more difficult to avoid utility lines when using HDD because of the limited visibility inherent in the process. There have been instances of boring drill bits penetrating underground gas lines that the operators did not know were in the vicinity or believed were located at different depths. Leaking natural gas that contacts an ignition source will explode into flames. Gas can also travel underground and explode in neighboring areas if ignited. Also, a struck underground electrical line can electrocute the drill operator. Because of the nearly blind aspect of trenchless drilling, these risks cannot be completely eliminated. But a strong safety and prevention program that both follows OSHA requirements for construction and addresses the unique risks of HDD will go a long way to avoiding accidents, injuries to workers and others, and potentially catastrophic property damage.

Avoid utility lines

The risk of most concern with HDD is striking underground natural gas or electric utility lines, a risk that increases when HDD is used in urban areas. To avoid hitting lines, the presence and location of the lines should be identified by using surface markings.  Since underground lines can be difficult to identify if they are covered by other lines, are sometimes 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. Specifically:

  • 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 to verify underground utility locations.
  • Compare findings with surface markings to identify any missed utility.
  • Employ potholing and other safety precautions 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 any underground utility installations in the work area. However, 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.


Potholing involves digging small test holes along the planned drilling path to verify the location of underground utility lines. The tracker is able 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.

Potholes can be dug by hand, which can be labor intensive if lines are deep; also, hand digging can damage lines. The preferred—and more costly—method is the use of a vacuum excavator. Regardless of the method, potholes must go to the planned drill path's depth—even if this is beyond the deepest known utility line—to identify any hidden lines.

Safety assessments

Before starting HDD, employers should 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 (PPE). In addition to the potential danger of striking an underground utility line, other HDD hazards include mechanical rotating parts (e.g., struck-by or caught-in hazards) and high-pressure drilling fluid. The following safety precautions should be taken:

  • 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. Contact utility companies about discrepancies.
  • 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 to the planned drill path's depth to expose any hidden underground utilities.
  • Train HDD machine operators and trackers before starting the operation on how to communicate effectively with hand signals and radios.
  • Ensure trackers check the tracking device readings frequently during HDD operations, and compare them with the preoperational walk-through 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; trackers should guide the HDD machine operator along the bore path to avoid striking a line; and
    • 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.


In addition to the above recommended safety practices, employers must comply with all applicable local, state, and federal regulations, including those issued by OSHA, the Department of Transportation’s Pipeline and Hazardous Materials Safety Administration, the Federal Aviation Administration, the Federal Highway Administration, and the Federal Railroad Administration. Specific OSHA regulations that will apply in an HDD operation include:

  • PPE (29 CFR 1926.95(a)). PPE, which includes protection for eyes, face, head, and extremities; protective clothing; respiratory devices; and protective shields and barriers, must be provided, used, and maintained in a sanitary and reliable condition wherever it is necessary by reason of hazards of processes or environment, chemical hazards, radiological hazards, or mechanical irritants encountered in a manner capable of causing injury or impairment in the function of any part of the body through absorption, inhalation, or physical contact.
  • Fire protection and prevention (29 CFR 1926 Subpart F). The employer is responsible for the development of a fire protection program to be followed throughout all phases of construction and demolition and must provide firefighting equipment that is maintained at all times and is conspicuously located.
  • Smoking (29 CFR 1926.151(a)(3)). Employers must prohibit open flames and smoking at a worksite when conducting HDD operations.
  • Emergency action plans (29 CFR 1926.35). Employers must develop emergency action plans that cover actions employers and employees must take to ensure employee safety from fire and other emergencies. Minimum elements of plans include emergency escape procedures and emergency escape route assignments; procedures to be followed by employees who remain to operate critical operations before they evacuate; procedures to account for all employees after emergency evacuation has been completed; rescue and medical duties for those employees who are to perform them; the preferred means of reporting fires and other emergencies; and the names or regular job titles of persons (or departments) who can be contacted for further information or explanation of duties under the plan.
  • Training (29 CFR 1926.21). The employer must instruct each employee in the recognition and avoidance of unsafe conditions and the regulations applicable to his or her work environment to control or eliminate any hazards or other exposure to illness or injury.
  • Qualified employees (29 CFR 1926.20(b)(4)). The employer may permit only those employees qualified by training or experience to operate equipment and machinery.


Apart from safety issues, HDD will almost always cost more per linear foot than traditional trenching. But, again, HDD usually causes far less surface disruption and is also viewed as more environmentally friendly than trenching. The decision to trench or use HDD should, therefore, be based on site-specific conditions as well as budget.

William C. Schillaci

Copyright © 2022 Business & Legal Resources. All rights reserved. 800-727-5257
This document was published on
Document URL: