Washington (CNN) -- The National Transportation Safety Board on Monday issued seven recommendations, calling six of them urgent, as the result of its investigation into the fiery natural gas pipeline explosion that killed eight people and destroyed 37 homes in San Bruno, California, four months ago.
The safety board said record-keeping problems could create conditions in which pipelines are operated at higher-than-allowable pressures, but added, "It is not known at this time if that is what happened," in the September 9 San Bruno accident.
Nonetheless, the board said the investigation could have far-reaching ramifications for the nation's gas transmission lines, and it voted to hold a fact-finding hearing into the San Bruno explosion.
"This accident has exposed issues that merit further attention and have implications for the pipeline infrastructure throughout the country," NTSB Chairwoman Deborah Hersman said in a prepared statement.
The massive explosion in the pipeline, which was installed around 1956, created a 72-foot long, 26-foot wide crater, and residents of the San Francisco suburb originally thought an airliner had crashed there. A 28-foot pipe segment was found about 100 feet away from the crater.
NTSB investigators found that although the pipeline operator, Pacific Gas and Electric Company, indicated the pipeline in the area of the rupture was constructed of seamless pipe, it was partially constructed of seam-welded pipe. Some of the seams were welded from the inside and outside of the pipe, while others were welded only from the outside, the NTSB said.
The NTSB said it is concerned that the seam-welded sections may not be as strong as the seamless pipe that was indicated in PG&E's records.
"Because it is critical to consider all of the characteristics of a pipeline in order to establish a safe maximum allowable operating pressure (MAOP), the NTSB believes that these inaccurate records may lead to potentially unsafe MAOPs," the NTSB said in a statement Monday.
The urgent recommendations call on pipeline operators and regulators to ensure that the records, surveys and documents for all pipeline systems accurately reflect the pipeline infrastructure as built throughout the United States so that maximum safe operating pressures are accurately calculated.
In a previous release, the NTSB noted that the pipeline may have been operated at pressures exceeding its "specified maximum operating pressure of 375 pounds per square inch gauge (psig). According to PG&E, the maximum allowable operating pressure for the line was 400 psig.
Just before the accident, the NTSB said PG&E was working on a power supply system at a facility about 40 miles southwest of the site. During that work, the power supply malfunctioned, killing an electronic signal to a regulating valve for the pipeline. As a result, the pressure increased to 386 psig, while pressure at a downstream station built to 390 psig.
The NTSB Monday issued three safety recommendations, two of which it classified as urgent, to PG&E. It is asking the utility to search its records to identify all gas transmission lines that had not previously undergone tests designed to validate a safe operating pressure and to determine the maximum operating pressure based on the weakest section of pipelines.
Saying record discrepancies could potentially compromise pipelines throughout the U.S., the safety board also made an urgent recommendation to the Pipeline and Hazardous Materials Safety Administration (PHMSA) to inform the pipeline industry of the circumstances of the San Bruno accident and investigative findings. That will allow operators to implement corrective measures, the NTSB said.
"While it may seem like a small paperwork error, if companies are basing operating pressures on inadequate or erroneous information contained in their records, safety may be compromised," Hersman said.
The NTSB also directed three urgent recommendations to the California Public Utilities Commission (CPUC), which regulates PG&E and other California pipeline operations. CPUC was asked to ensure that PG&E "aggressively and diligently" search documents and records, and CPUC was asked to inform California operators of the circumstances of the San Bruno accident so these operators can likewise proactively implement any corrective measures for their pipeline systems.
The NTSB said it will hold its hearing on the San Bruno accident on March 1 and 2 in Washington.