What is the goal of damage prevention?

Damage prevention focuses on mitigating the risk of endangering lives and the loss of money. Adherence to best practices and use of the latest recognized methods can substantially ameliorate both.

1. First, define the nature of the risk. What is the potential for injury or death and what, if any, potential costs can be accommodated?
2. Next, define the costs of mitigating the risks. What are the costs of using systematic damage prevention methods to reduce the risk?
3. After following best-practice damage prevention, what residual risk remains?
4. How will the residual risk be managed? Should one use insurance, attempt to contract away the liability, or just ignore it?

Proactive damage prevention for subsurface construc¬tion incorporates the following elements:

1. Exploit all knowledge of land use history including old records, photographs, drawings and even people’s memories (eye witness accounts).
2. Investigate and classify direct observations of above-round indicators such as poles, pipes, monu¬ments, caps, etc.
3. Utilize subsurface detection systems to map all detectable underground objects.
4. Employ systematic site marking and labeling.
5. Use invasive testing and careful excavation methods.
6. Compile and/or update drawings and database re¬cords with field locates and intrusive testing findings.
7. Educate all contractors and workers about the marking system conventions, excavation procedures and risk factors.

This discussion focuses on point (c) above, the technol¬ogies that ‘sense’ the presence of subsurface objects using phenomena that obey the basic laws of physics. There are no magic solutions – only sound science, adherence to proper procedure and intelligent use of the observations.

Sensing Technologies

Most sensing technologies use electric and magnet¬ic fields or acoustic signals to detect the presence of underground objects. All technologies depend on the signals interacting with the buried objects in a manner that uniquely determines the presence and position of a buried object. Further, the operator must be provided with a simple, systematic means for marking the posi¬tion of the detected object.

Three technologies are most frequently used for locating buried utilities and similar structures:

1. The most common is the traditional pipe and cable locator which detects magnetic fields associated with electric current flow on a buried pipe or cable. Logical¬ly, this requires a metallic structure or tracer wire to carry the electric current.
2. Magnetometers are occasionally used to detect magnetic fields from buried ferrous objects. Unfor¬tunately, few buried utilities are composed of ferrous material.
3. Ground Penetrating Radar (GPR) uses radio waves to image the subsurface. GPRs contain a transmitter which directs radio waves into the ground. Subsur¬face objects are detected by sensing the radio waves reflected from the object.