The C-hook that failed on a PG&E high-voltage transmission line on Nov. 8, 2018, sparking the Camp Fire. (PG&E via U.S. District Court for Northern California)
In the latest twist in the saga surrounding how PG&E maintained the high-voltage power line that sparked California's deadliest wildfire, the company is acknowledging that it received troubling information about a key piece of hardware used on its transmission towers more than 30 years ago, but is unable to say what steps, if any, it took in response.
In a federal court filing Thursday, the company confirmed part of a recent NBC Bay Area report that it had conducted tests of "C-hooks" used in connecting insulators and power lines to transmission towers.
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The hooks and their maintenance history are the focus of attention because a badly worn C-hook on a PG&E transmission tower in Butte County snapped early the morning of Nov. 8, 2018, allowing a charged piece of cable to swing free. The resulting arc sparked the Camp Fire, which destroyed most of Paradise and two nearby communities and killed 85 people.
In its Thursday response to a series of 10 technical questions from U.S. District Judge William Alsup, who is overseeing the company's criminal probation for federal pipeline safety violations, PG&E released a 1987 report that briefly outlined concerns about worn hooks discovered on a Contra Costa County transmission line and reported the results of strength tests on the hardware.
The 1987 report says a PG&E transmission and distribution manager asked for the tests on a pair of worn hooks "because there was a concern that they may not be able to hold the weight of insulator strings that are suspended from them."
A worn suspension hook, variously referred to as a C-hook or J-hook, found on a PG&E high-voltage transmission tower in Contra Costa County. The hook, which a PG&E lab said may have suffered wear from supporting swinging power lines, underwent testing in early 1987 and failed at far less than its design strength.
PG&E tested two worn hooks, which had been removed from a tower on the Oleum-G transmission line in Contra Costa County, along with a third hook that had no visible sign of wear.
The hooks had an "ultimate strength" rating of 30,000 pounds — the predicted amount of force that could be applied to them before they failed. But in the tests, the worn hooks from the Oleum-G line failed at just 11,500 pounds. The third, apparently undamaged, hook failed at a much lower point.
“The hook without visible flaws failed at 6,900 lbs. and the rating for these hooks is 30,000 lbs," the report observed. "This would suggest that a test be done on some random samples of different manufacturers’ hooks from PG&E stores to check their strength against specifications.”
In its Thursday filing, PG&E said it had been unable to find any evidence that the recommended testing had taken place.
"PG&E has searched for records relating to any such strength testing during the late 1980s but has not located any such records that have been retained," the company's lawyers wrote.
The new document also rejects expert opinions reported in the Dec. 11 NBC Bay Area report about the 1987 tests that "PG&E was aware of a big problem and did nothing to solve that problem," and that the company "knew there was a problem for 30 years."
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The company said that those statements ignored its program of transmission line inspections. For the tower involved in starting the Camp Fire, PG&E has said it conducted routine ground inspections every five years and that aerial and infrared inspections were conducted repeatedly on the associated transmission line.
But the California Public Utilities Commission noted in its recently released investigative report on the Camp Fire that PG&E crews had not performed a close-up climbing inspection of the tower that sparked the fire since at least 2001.
"This omission is a violation of PG&E's own policy requiring climbing inspection on towers where recurring problems exist," the report said. "... A climbing inspection of the incident tower during that time could have identified the worn C-hook before it failed, and that its timely replacement could have prevented ignition of the Camp Fire."
PG&E's new filing notes that the utility's 50,000-plus transmission towers include hundreds of thousands of C-hooks.
In answer to a specific question from Alsup about whether the company had ever noticed any worn C-hooks or hanger plates — devices that secure the hooks to towers — prior to the Camp Fire, PG&E listed about a dozen cases of wear involving hooks on about 70 towers dating back to 1987. It noted two other occasions where hooks failed in the decade before the Camp Fire.
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