Interpretation Response #PI-82-0113
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PI-82-0113
U. S. Department of Transportation
Research and Special Programs Administration
400 Seventh Street, S.W.
Washington, D.C. 20590
December 27, 1982
The Honorable Jim Leach
U.S. House of Representatives
Washington, D.C. 20515
Dear Mr. Leach:
This refers to your communication of December 7, 1982, requesting our consideration of a letter from Bonnie T. Eggers regarding the proper depth at which gas pipelines should be buried. Ms. Eggers' concern stems from the death of two relatives in a recent pipeline accident at Hudson, Iowa.
The Federal safety standards for gas pipelines are set forth in Part 192 of Title 49 of the Code of Federal Regulations. These standards were issued under the Natural Gas Pipeline Safety Act of 1968 (49 U.S.C. 1671 et seq.). Section 192.327 of the standards requires that buried transmission lines in rural areas, like the one involved in the Hudson accident, be constructed with at least 30 inches of soil cover or 18 inches of rock cover. The required cover increases to 36 inches and 18 inches, respectively, for areas with a higher population density. These burial depths exceed the depths that were recommended for gas pipelines by the American Society of Mechanical Engineers in its B31.8 Code for pressure piping that was in effect when the standards were adopted.
The purpose of the prescribed depths is to reduce the likelihood that a buried pipeline will be damaged by normal cultivation or other digging activities. While a greater burial depth might logically be expected to further reduce this likelihood, there is no empirical evidence supporting the proposition that increasing burial depth would be cost-effective from a safety perspective.
In contrast, experience has shown that measures such as line marking, mapping, and advance coordination of construction work provide more effective and economical approaches to damage prevention than deeper burial. In this regard, the Federal safety standards require operators of buried pipelines in rural areas to install permanent marking signs along the pipelines to show their location. Each sign provides a warning, the name of the operator, and a telephone number that an excavator may call to learn more specific information about the pipeline before beginning to dig. Another standard that was recently adopted for pipelines in populated areas (47 FR 13818; April 4, 1982) requires operators to provide a damage prevention program. Typically, under these programs an excavator calls a publicized number before digging, and the pipeline operator furnishes temporary marking at the job site. Such programs provide advance coordination between operators and excavators and are often run in cooperation with operators of other underground utilities. We will be monitoring the effects of the various damage prevention programs established under the new regulation before taking any further rulemaking action toward prevention of outside force damage to buried pipelines. The protective measures that the Federal standards provide are, of course, not infallible. I understand that the pipeline involved in the tragic Hudson accident had been temporarily marked before it was damaged by the trenching equipment. Human error, particularly by excavators outside the pipeline industry and the reach of our jurisdiction, will inevitably continue to be a causal factor in pipeline accidents despite the most diligent Federal regulatory efforts.
I trust this adequately responds to your inquiry, but should you need additional information, do not hesitate to contact me.
Sincerely,
Howard Dugoff