Underground utility contractors are familiar with horizontal directional drilling (HDD). In fact, many underground utility construction firms use HDD equipment to complement open-cut excavation to install utilities.
In some situations, HDD offers many advantages, including efficiency, speed, cost-savings and less disruption to the environment and traffic flow. Although it does not eliminate the need for open-cut utility construction, it is another tool in the contractor’s arsenal of machines and methods.
From the safety perspective, no method is perfect. As with open-cut utility construction, HDD has its share of hazards that must be controlled or eliminated in order to ensure worker and public safety. The biggest problem that all directional drillers face is striking existing underground utilities. Therefore, the first step in preventing damage is that the contractor must call Dig Safe or the local one-call center for a locate to get the existing utilities marked and physically identified. Without a doubt, these are probably the two most important things an HDD contractor must do before beginning any job.
Once the horizontal location is known and the utilities have been exposed to determine their depth at regular intervals along the drill path, the next step is to start drilling. The drill head should be tracked by an experienced worker using a tracking device so he/she can direct the operator to steer the drill over, under or around the existing utilities. Just going deep under existing utilities is not the answer and often leads to serious problems. Many directional drillers have drilled deep only to find that somebody else had the same idea before them.
After utilities are marked on the surface, they should be exposed at regular intervals along the drill line to ensure they are where they should be. Hand dig or use vacuum excavation to expose existing utilities. It is important for crews to remember that marks/flags on the surface of the ground only provide the approximate horizontal location of underground utilities. The only information you can expect to obtain from the Dig Safe locator is the approximate line on which the utility was installed. Don’t expect them to tell you the depth of the utility.
Take extra care when planning a drill path parallel to an existing utility. Pipelines may have valves, tees or other connections protruding into the drill path. Buried cables may not have been installed in a straight line and excess cable loops are often buried.
Always double-check the area around the drill path for any evidence of an existing utility that may not have been marked by the locator. Look for pedestals, pole risers, drops, manhole covers, storm drain outlets, meters, utility structures, etc. Remember that sewer and water lines are often overlooked and not marked because many states do not require all facility owners to be members of the one-call system.
Another area of considerable concern that affects drilling contractors is that laterals to homes and businesses are not generally marked. There have been numerous incidents where contractors have drilled through sewer laterals followed by installing a gas line through the lateral. The consequences of such an action is a clogged sewer lateral followed by a plumber clearing the line and a gas explosion. People have been fatally injured and property severely damaged when this type of situation occurs.
Before drilling, make sure the workers have been trained to perform their tasks and they have the right safety equipment. Inspect all equipment, including safety equipment, to make sure it is in good condition.
The Association of Equipment Manufacturers (AEM) recommends that all workers wear properly rated, electrically insulated footwear at all times, including during setup, drilling and other activities. Proper footwear will reduce the possibility of a worker being electrically shocked if contact is made with an underground electric cable that could create ground voltages, some of which could be deadly. Workers should wear eye protection, electrically insulated rubber gloves, highly visible clothing and, in some situations, hearing protection.
The drill head must always be tracked to ensure that it stays on course. Tracking devices use electromagnetic fields to detect and track the drill head. Before starting work, check for sources of interference.
AEM suggests the following: “Walk the planned drill path with the drill operator. Turn your tracking receiver on but leave the transmitter off. Look for signal strength variations or other unusual readings and mark these locations.”
Active sources of interference include but are not limited to:
- Traffic-sensing loops and traffic signal pads,
- Electric dog fences
- Buried utility line with cables or trace lines that transmit high frequency signals
- Other transmitters such as radio and TV transmission facilities,
- Cathodic protection currents,
- Microwave or radar transmission facilities,
- Thunderstorms, and
- Other locating equipment being used in the same vicinity.
- Passive sources of interference include but not limited to:
- Underground metal structures such as tanks,
- Towers and vehicles,
- Reinforced-concrete roadways, sidewalks and driveways,
- Steel or cast-iron pipes, and
- Proximity to salt water.
The drill operator and the tracking equipment operator must communicate. Before starting the job, they should discuss the planned drill path and any potential problems or obstacles, including sources of interference. They should also establish a means of communicating with each other. Two-way radio communications are considered the best method. Communications must be clear and all directions must be confirmed. Hand signals are another option but a line of sight must be maintained and a set of pre-established signals must be established.
If unexpected or inconsistent readings are encountered, stop drilling. Cross-check all information and find the problem. If readings are still wrong, pull back to the last known drill-head position and verify that the equipment is working properly. Do not start drilling again until the problem is found and corrected.
When crossing or working near an existing utility, slow down and allow enough room for the back-reamer to clear with space to spare during the pullback. Don’t back fill a pothole until the back-reamer is clear and you are sure the existing utility is undamaged.
There are a number of potential hazards that workers could be exposed to. These hazards should be discussed with workers during training. Struck-by hazards are the most common cause of employee injuries. Employees should be instructed not to use pipe wrenches to separate the pipe string. There are special tools known as tongs for this purpose. A pipe wrench can slip. Workers have also been known to strike wrenches with hammers or even use the backhoe to press on the wrench only to have it spring free and strike somebody.
Coiled plastic pipe is another potential source of workers being struck when it is uncoiled or when being cut. Poly-pipe should be restrained when cut, and workers should be aware of its ability to unravel violently. Workers should also wear eye protection at all times.
Although common to any type of work along the road, workers can be struck by moving vehicles. Workers should not enter into the roadway except when absolutely necessary and they should wear high-visibility clothing at all times so that they are visible to drivers and equipment operators.
Workers should always stay clear of the rotating drill and shaft. Never allow workers to stand on or straddle the drill string. Workers should not stand in the receiving pit or area where the drill is expected to exit.
Other hazards include the possibility of being electrocuted if a power line is hit. Therefore, they should not be touching the pipe string or equipment when the drill is being pushed into the ground. Only the operator should be in contact with the equipment and he/she should follow the manufacturer’s procedures. If a gas pipe is hit during drilling, everybody in the area should be notified and get away from the work area and equipment. In both situations, 911 and the utility company should be notified immediately.
George Kennedy is NUCA vice president of safety.