WASHINGTON — Prompted by 40 deaths apparently caused by faulty plastic pipe used in natural gas lines, a federal agency is suggesting that some of the pipe is prone to crack and that regulators need to examine the problem.
The April 14 report from the National Transportation Safety Board said explosions caused by brittle plastic pipe killed six people in Waterloo, Iowa, in 1994, 33 people in San Juan, Puerto Rico, in 1996, and one person in Lake Dallas, Texas, in 1997.
``Much of the plastic pipe manufactured and used for gas service from the 1960s through the early 1980s may be susceptible to brittlelike failures when subjected to stress intensification, and these failures represent a potential safety hazard,'' NTSB said.
Plastic pipe used in natural gas transmission is predominately high density polyethylene.
Industry officials and an official with the Department of Transportation's Office of Pipeline Safety raised questions about how widespread the problem is in pipe from that period.
Richard Felder, associate administrator of OPS, said the pipe in the Iowa explosion was a problem and virtually all of that pipe has been replaced. But he said DOT's pipeline officials ``are not aware of the same problem with other manufacturers.''
NTSB concluded that brittlelike failure is the second-leading cause of plastic pipe failure, after excavation damage. Felder said that is not consistent with OPS data.
``Certainly in response to this report, we will re-canvass,'' Felder said. ``We want to address whatever concern the NTSB has.''
The brief NTSB report said that current data is not sufficient to assess the long-term performance of plastic pipe, and that the tests used to measure plastic pipe from the 1960s to the early 1980s may have overrated its strength.
NTSB said it interviewed experts and spoke with gas companies. The full NTSB report is due out in six to eight weeks.
In the Iowa incident, NTSB said plastic pipe from Century Utility Products Inc. and Union Carbide Corp. had poor resistance to brittle cracking.
A Union Carbide spokesman said the company is reviewing the report but said the pipe met the standards for the era.
Felder said the Puerto Rico and Texas incidents were caused by other factors that caused the pipes to fail, not inherent problems with the material.
Richard Gottwald, executive director of the Plastics Pipe Institute, a unit of the Society of the Plastics Industry Inc., in Washington, said today's pipe is much improved. He added that even in the period in question, plastic pipe had better leakage rates than steel.
An official with the American Gas Association in Arlington, Va., said the majority of pipe installed today in local distribution systems is plastic because it is ``far superior'' to steel and cast iron.
``What we don't want to happen as a result of this report is there to be a fear that there is a widespread problem,'' said Lori Traweek, AGA's vice president of operations and engineering.
The pipe used in long-distance lines are steel, but plastic dominates local systems. Of more than 400,000 miles of plastic pipe used in 1990, 95 percent was polyethylene, according to NTSB. In 1978, there was roughly 178,000 miles of plastic pipe used, 85 percent of it PE.