The hooks and their service history are the focus of attention as a badly worn C-hook on a PG&E transmission tower in Butte County broke early in the morning on November 8, 2018, allowing a loaded length of cable to swing freely. The resulting arc started the bonfire that destroyed most of Paradise and two nearby communities, killing 85 people.
In its Thursday response to a series of 10 technical questions from US District Judge William Alsup, who oversees the company’s criminal probation for federal pipeline safety violations, PG&E released a 1987 report which 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 states that a PG&E transmission and sales manager requested the tests on a pair of worn hooks “because of concerns that they might not be able to support the weight of the isolator cords suspended from them”.
A worn suspension hook, also known 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 worn out from supporting vibrating power lines, was tested in early 1987 and failed at far less than its design strength.
PG&E tested two worn hooks that had been removed from an Oleum-G transmission line tower in Contra Costa County, along with a third hook that showed no visible signs of wear.
The hooks had an “ultimate strength” of 30,000 pounds – the predicted amount of force that could be applied to them before they failed. But in testing, the worn-out hooks on the Oleum G line failed at just 11,500 pounds. The third hook, apparently undamaged, failed at a much deeper point.
“The hook with no visible defects failed at 6,900 lbs. and the rating for these hooks is 30,000 lbs,” the report noted. “This would indicate that a test will be run on some samples of hooks from different manufacturers from PG&E stores to check their strength against specifications.”
In its Thursday filing, PG&E said it could not find any evidence that the recommended testing had taken place.
“PG&E searched for records of such strength tests in the late 1980s but found no such records that were preserved,” the company’s attorneys wrote.
The new document also dismisses expert opinion reported in the December 11 NBC Bay Area report on the 1987 tests that “PG&E was aware of a major problem and did nothing to address it” and that the Company “knew there was a problem”. 30 years.”