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DOE-HDBK-1092-2004
currents, differential heat, and thermal reflection are also available. Here are three types
presently in use :
a. Terrain Conductivity uses the VLF range, using Eddy Currents to measure
differences in ground conductivity. It has proven useful in locating very deep or short
metallic utilities and air/gas-filled utilities.
b. Ground penetrating Radar uses 1-100 gigahertz microwaves measures reflections
due to dielectric differences in subsurface materials. It measures strength and
amount of time necessary to bounce signal off different layers. This technology
requires resistant soils. Utilities must be of sufficient size to be detected. The deeper
the utility, the larger it must be in order to be detected. Highly different soil/utility
materials give the best results.
c. Thermal measures heat output. When the amount of heat from the utility is different
from that of the surrounding soil, it might be detectable. Some utilities produce their
own exothermic heat or retain heat longer than the surrounding soil.
Choosing the appropriate locator technology and methods will greatly improve the chances
of success.
11.4.3 LOCATOR OPERATOR TRAINING
Each piece of locating equipment is unique. It is very important that operators be trained to use
the equipment before applying it in a field application that will determine safe boundaries for
excavation workers. Some of the ground penetrating radar equipment is very dependent on
operator interpretation of the characterization profiles generated from the locator equipment.
Operators unfamiliar with the equipment specifications and operating instructions can make
interpretive mistakes which can lead to serious injury to the excavation workers.
Proper selection of available techniques and the use and interpretation of data produced by this
equipment is essential to the accurate and comprehensive detection of underground utilities. A
regular calibration and maintenance of locator equipment should be established.
11.4.4 FIELD MARKING OF IDENTIFIED UTILITIES
Paints/Surface Markings are used at many jobsites. Care should be taken to ensure the
markings are clearly present and identifiable at the time the excavation workers arrive at the
excavation site. Many cases of faint markings and/or markings washed away by rain have been
documented at jobsites. The recent use of biodegradable survey paints has increased this
possibility. They are not as durable as former types of survey paints used. Lawn mowing
equipment can erase or diminish the effectiveness of survey paints in outside areas.
Stakes or Flags are used to mark identified utilities at other jobsites. These must be durable,
as well. They must be able to withstand the environments they are exposed to. Lawn mowing
equipment can erase all traces of survey flags in very short order. Incidents resulting from
missing and even relocated stakes or flags have been documented.
Utilities Color Coding is used at most work locations. The standard utilities color-coding is
well understood by most excavations subcontractors, and serves as a very effective
communications tool for the facility owner.
11-6


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