Photos obtained by NBC Bay Area’s Investigative Unit reveal that several hooks on the Caribou-Palermo transmission line after the Camp Fire last year show significant long-term wear — besides the hook that failed and sparked the fire.

Experts who reviewed the photos say some wear was so extreme it should have been readily evident during any detailed inspection. The company relied mostly on aerial and ground patrols of the line before the fire, not climbing inspections.

Some 80 last-minute climbing inspections also failed to uncover any serious threats, despite the wear visible in the photos of several hooks and steel hanger plates.

“This is bad as you can get — this is terrible.” said Dan Mulkey, a four-decade veteran electrical engineer with PG&E who is now a consultant. “I can’t imagine how it got that bad and no one saw it — it’s flabbergasting,”

It was a worn C-hook on Tower No. 27-222 on the nearly 100-year-old line that failed and caused the 115,000-volt line to hit the tower and spark the fire that destroyed the town of Paradise and left 85 people dead.

But photos of a hook on another tower just 3 miles away showed significant wear due to what engineers call “fretting erosion.”

One of the eroded hooks appears to have only about a 16th of an inch of steel left.

“When I saw that hook, I said, ‘Oh my goodness … I’ve got the welfare of an entire community hanging by that hook,’’’ said Bob Bea, an engineering professor emeritus at UC Berkeley who studies manmade disasters.

Bea said the damage he saw would not have happened overnight – it is the product of decades of rubbing of a hook and the hole in the steel plate that they hang from.

“Those two surfaces sand each other,” Bea said. “So one surface wears into the other surface; it takes a long time to develop, with high stresses and sometimes water.”

Bea said all the factors were at work on the towers of the Caribou-Palermo line, with wear both on the hooks and the plates that hold them in position. One plate appears to have completely worn out.

“It’s amazing it was still up in the air — with that much damage,” Mulkey said. “That level of damage, it really makes me wonder about the whole inspection — what the heck is going on? You are not finding things that should be obvious and things that are absolutely critical. How much more is there out there?”

The company said in a statement that the line has been shut down since December 2018 and permanently decommissioned as of June.

The company has since inspected some 50,000 transmission towers and structures, 700,000 distribution poles and 222 substations — covering more than 5,500 miles of transmission line and 25,200 miles of distribution line in high fire-threat areas. The inspections, the company says, “looked at all aspects of PG&E assets, including cross-arms, insulators and footings, along with critical electrical components and equipment. PG&E and contract crews inspected electric towers and poles from top to bottom through ground, climbing, helicopter or drone inspections.”

The company identified more than 11,000 problems in high fire zones, about 1,000 of them considered critical. It found 18 critical problems on the Caribou-Palermo line, what it called a “significant number” and brought in an outside consulting firm at the request of state regulators “to conduct a records-based review” of that line. State regulators say that firm’s report is not yet final.

Meanwhile, the company says it now uses “a risk-based approach to identify components on electric towers and poles that have an increased risk of potential wildfire ignition. And, we are using new technology such as drones as part of these enhanced inspections.”

PG&E Wildfire Safety Inspection Program

This map shows high priority cases that PG&E identified in the weeks and months after the Camp Fire. As of Aug. 31, 2019, 1677 out of 11260 total cases were open. Cases labeled with an "A" tag require immediate action, whereas "B" cases generally need to be addressed within three months, according to PG&E. Click or hover above a case to see more information.