By Daniel C. Brown

Horizontal directional drilling (HDD) has dramatically changed the way underground contractors place underground utility lines, from gas and electricity to water and television cable. Relative to trenching, HDD often offers greater productivity, less surface disruption, and lower material handling costs.

But along with those benefits come very serious dangers. Probably the most prevalent one is a utility strike. The most dangerous strikes can occur when a drill hits an electric or gas line. The drill operator or person guiding the bore can be electrocuted. And gas line strikes can cause explosions. In recent years, gas line explosions have resulted from strikes by directional drills working in both Maryland and Colorado, causing significant property damage.

Accidents also can result from the improper use of HDD machines and related equipment. Workers can be caught and seriously injured or killed in rotating drill equipment.

The good news is that the HDD industry has learned a great deal about how to prevent these accidents. All states have one-call systems that result in utility "locates." Recently, says Gregg Austin, product safety and compliance engineer with Vermeer Manufacturing Company in Pella, IA, Congress passed legislation that will make available one national three-digit number that will refer people to the state or local one-call service.

While a complete review of HDD safety practices is beyond the scope of this column, we'll spotlight here some of the more vital points for contractors. The first is to plan and map your bore. Make sure that you plan the pipe depth and route so that the bend radius of your product pipe can go around or well under any obstacles. With a bore plan in hand, a competent person must visit the site and mark the route of the line. Next, a call goes out to the state's one-call locating service, and the utility owners typically send out persons trained to mark their utilities.

Exposing the existing utilities comes next. "There is an OSHA requirement to expose all utilities before you dig or drill," Austin says. That job is up to the HDD contractor. You can manually dig—or you can "pothole" the utility using vacuum excavation or a hydro-excavation machine with a water jet. Austin cites OSHA CFR 29 1926.651 as the rule requiring utility exposure.

You want to do enough potholes so that you don't miss any utilities—their locations may vary from the marks. "Locates may not show how electrical lines have been looped at splice points," according to a new safety video from the Underground Contractors Association of Illinois. Obviously, more potholes cost more money, but utility strikes are expensive—and dangerous.

Take care with the information from your bore-tracking devices, warns an industry safety video produced by the Association of Equipment Manufacturers (AEM). All current bore-tracking devices use electromagnetic fields, and the fields are subject to interference. Such interference can be active, as with radio and TV transmitters and electronic dog fences. Or they can be passive sources, such as reinforcing steel in concrete. You should resolve deviations in bore-tracking information, such as pitch information that is not consistent with depth information. "Rely on common sense and factor in drill pipe length, pitch, ground conditions and thrust pressure," notes the AEM video.

Before the bore starts, secure the job site, Austin says. Keep spectators away, especially if you're drilling around electrical lines. If an electrical strike occurs, the ground can become energized and people can be shocked and possibly electrocuted.

It's important for the drill operator to establish good communication with his tracking operator out in front. Good visual contact is not always possible, so you must set up radio protocols ahead of time. The use of a two-way radio can be tricky—every command should be fully confirmed by the receiver. By the careless use of a radio button, "Don't rotate" can become "Rotate."

Austin points out another major safety rule: Don't work on the drill string unless the drill string is disabled. To disable the drill string, some manufacturers offer radio-controlled lockout systems. Or, when the drill comes out in the exit pit and it's time to change tools, make it a rule for the operator to carry the machine's keys to the exit pit. If the drill strikes an electric line, the drill operator should back up the drill and stay on the machine; dismounting the machine could result in electrocution. The operator should follow the manufacturer's procedures to determine if the machine is electrically charged. The tracking operator should stay in place; the ground may be charged. Be aware that some electric utilities have an automatic reset feature that will re-energize the wire. The industry video strongly warns against persons on the ground touching the machine, the drill pipe, the water system, the mud mixing system—or anything connected with the drill. Touching those things could result in electrocution.

Have someone call 911 or another emergency number. Then contact the electrical utility. "Do not restart the drill until cleared to do so by the electrical utility," warns the industry video.

If a gas line strike occurs, don't move the drill string. Any movement could cause a spark that will ignite the gas. Everyone should evacuate the area immediately, the industry video says. Secure the area, call 911 or another emergency number, and notify the utility. Do not resume drilling until cleared to do so by the utility.

Working safely requires a respectful attitude toward the hazards discussed here. It's not difficult to be informed—but it does take some time and training.

Daniel C. Brown owns TechniComm, a construction industry communications firm.

GEC - November/December 2004