This electrical transmission tower has a little problem. can you spot it? Actually, it's not a small problem -- it cost us 16.65 *billion* dollars and caused the deaths of 85 people. [...]Remember that worn C hook? How long was it rubbing against the hangar bracket? The answer is that we don't know. we think it is about 97 (!) years old, but we're not sure because PG&E didn't keep records about it.
After the fire, many of the pieces were taken to the FBI lab's metallurgical unit at Quantico, and they determined that the C hook was made of cast iron. Not all the C hooks on these 100-year old towers were made of cast iron -- many were made of steel. But again: no records.
PG&E knew that this was a problem because at some point they bolted on L brackets and moved the C hooks onto the new brackets, probably concerned that the old bracket hole had mostly worn through. we don't know when they did this because they kept no records.
And yes, PG&E is legally required to inspect these towers periodically. We don't know exactly when, because (you guessed it) no records from before the year 2000.
The investigating team interviewed troublemen (inspectors for PG&E) to find out exactly how they did the inspections. They were done mostly from helicopters. and despite having official procedures, here's what they did:
☑️ Is the tower still standing?
Their helicopters in Mountain View over the past several months have all been being about using ground penetrating radar so they could find the gas lines so they could perform accurate acoustic tests on them to see if they were stressed enough to blow up.
That makes me think of the "Front Fell Off" skit: "I'm not saying that tower wasn't safe, just perhaps not as safe as it could have been. Some of them are designed so the power lines don't fall off at all."
I was working in San Bruno at the time of the 2010 explosion. I recall reading in the local paper in the aftermath that San Bruno was not in the top 100 in PG&E's list of most dangerous sections of pipelines. I am still not sure what interpretation is most disturbing there: that there were at least 100 sections known to be more dangerous or that the list was (at best) incomplete and they had actually no idea which sections were dangerous. Either way, it's fair to say that they were very surprised when that section blew up.
The thing that upsets me the most about the San Bruno explosion is it took PG&E over an hour to shut the gas supply off and stop the flames. This was the difference between losing a few houses and destroying an entire neighborhood.
That can be the nature of gas pipelines, the residual pressure from everything connected downstream from the nearest available valve remains pressurized until the leak drains it even after it's shut off.
It wasn't just upstream pressure.
LA Times: "NTSB officials said PG&E took almost 95 minutes to shut off the gas spewing from the pipeline in San Bruno. The NTSB contends that a lack of automatic shut-off valves and valves that can be closed remotely contributed to the slow response."
Reminds me of the 2009 Black Saturday fires here in Victoria, partially caused by poorly maintained lines as well.
https://en.wikipedia.org/wiki/Black_Saturday_bushfires
It is beyond comprehension why PGE is allowed to exist.. to many obvious reasons to list..
One theory that I didn’t see pursued is that changing the bracket caused the hook to wear through faster. After 80-some years of wear, the original bracket hole was worn to fit the hook and rub over a large smooth surface. Changing the bracket meant the hook now swung against the 2 squared edges of the new hole, cutting it faster—unless they took steps to mitigate this. Also, if the new bracket was a harder steel/iron, it would also cut the hook faster.