The April 17 pipeline explosion at the Fresno Sheriff’s Foundation shooting range in northwest Fresno that killed one man and injured 12 others was caused by a Fresno County employee driving a front loader that struck the Pacific Gas & Electric Co. pipeline, a state report concludes.
The 260-page report prepared by Exponent, a consulting firm for the California Public Utilities Commission, was released Monday afternoon. It says the “PG&E line ruptured when it was struck by a front loader that was operating in the area at the time of the incident.”
The report adds: “The significant gouging, scraping and deformation present at the rupture location could only have been caused by contact with the front-loader bucket.”
The front-end loader was being driven by a county employee on a road formed over a berm that sat above the shooting range, near Highway 99 and the San Joaquin River. The explosion injured two sheriff’s deputies, the county employee and about 10 inmates, including one who later died of his injuries.
Several of the inmates, along with the county and the county worker, have sued PG&E, claiming improper maintenance of the pipeline.
The Exponent report is not the final word on the PUC’s investigation. A PUC spokeswoman said more work remains to be done before the PUC determines who was at fault.
In its report, Exponent ruled out the possibility of a bullet striking the pipeline and causing the 19-inch fracture that triggered the explosion.
“The front loader struck the pipe and punctured it, nearly instantaneously causing the rupture,” the report says. “The cause of the rupture cannot be attributed to inadequate material properties or manufacturing defects.”
The report says dirt covering the pipeline measured to nearly 4 feet except where it was punctured. There, the report says the “pipe was found to have minimal depth of cover at the strike location on the uphill side of the dirt road cut into the hillside.”
The pipeline met American Petroleum Institute standards, the report says. There were some irregularities in the pipe noted, but those did not contribute to the incident, according to the report.
The significant gouging, scraping and deformation present at the rupture location could only have been caused by contact with the front-loader bucket.
Report prepared by Exponent, a consulting firm hired to examine the ruptured pipeline
“No evidence of progressive cracking such as stress corrosion cracking or fatigue was observed,” the report says. “Only minor areas of corrosion were observed. Magnetic particle inspection found three crack-like indications that were the result of lack of fusion during original pipe manufacture. These indications did not contribute to the rupture.”
The pipe was 53 years old, but the report says it “did not exhibit signs of embrittlement, brittle fracture or progressive cracking.”
The cause of the metal deforming and fracturing was “application of forces that exceeded the strength of the material,” the report says.
PG&E spokesman Denny Boyles said the company continues to cooperate with the CPUC in its ongoing investigation, and that “our thoughts continue to be with the individuals who were impacted by this incident.”
PG&E officials said the Fresno pipeline was operating normally, with gas flowing at a pressure of 370 pounds per square inch, until just moments before the explosion when a drop in pressure was noted.
PG&E crews did a ground survey of the pipeline on April 1 and an aerial survey the day before the explosion and found no leaks in the line.
The testing and analysis performed by Exponent included a visual examination, dimensional analysis and other non-destructive examination, as well as “fractographic” examination, “metallographic” examination, mechanical testing, and compositional analysis.
Public Utilities Commission spokeswoman Terrie Prosper said the commission will use the report’s findings in its investigation of what caused the explosion, and whether PG&E violated any laws or regulations that might have contributed to the accident.
Assistant Sheriff Tom Gattie said Monday that he had not seen the report. The county’s hired lawyer, David M. Overstreet, also said he had not seen the report late Monday afternoon.
Overstreet filed a lawsuit on behalf of the county against PG&E two weeks ago. He said PG&E created a harmful condition at the site. The county suit says a county employee was “re-establishing a path on top of the berm (above the shooting range) when, without warning, the pipeline suddenly ruptured in a mechanical explosion, which created a large dirt cloud and sent debris far and wide. Shortly thereafter, a second explosion occurred, in which a giant fireball erupted.”
The county claims that PG&E “failed to exercise sufficient care” in inspecting and repairing the pipeline and did not ensure adequate soil depth covering the pipeline.
Lawyers for some of the inmates injured in the explosion say the investigation has a long way to go.
“I don’t know how they came to a conclusion on the depth of the pipeline since the ground was blown to smithereens,” said Butch Wagner, who represents three Fresno County inmates who were working at the shooting range the day of the explosion. “PG&E had a responsibility to make sure the soil compaction was significant enough to prevent something like a front loader from coming in contact with the pipeline.”
Warren Paboojian, who represents one of the inmates, said Monday that “the report is only one piece of the puzzle and we are not going to truly know what happened until we can take depositions.”
No inmates remain in the hospital, Fresno County Sheriff’s officials said. The driver of the front loader, Ismael Arreazola, also is no longer in Community Regional Medical Center following an extended stay for severe burns, a hospital official said Monday.