BART officials said Tuesday that Monday morning’s meltdown – the latest in a string of major service disruptions – was due to a still unexplained power surge near Montgomery station in downtown San Francisco. BART dispatch recordings show that the incident began at 6:52 a.m., when a train o perator reported to BART controllers that he had just witnessed a small explosion in front of his train, with smoke filling the tunnel at Montgomery station. “It was a loud blast as I was coming in,” the operator said. “The train went right through it. I couldn’t stop in time.” The operator reported there was “a lot of smoke behind me.” BART spokesman Chris Filippi issued a statement Tuesday saying at the time of the incident, there was a sudden power surge. BART Dec 8 BART service resumes after major delays due to power issue BART Dec 1 BART police to boost patrols through the holiday season San Francisco Nov 25 BART train operator reports explosion and fire occurring right in front of his train That surge triggered the system’s circuit breakers – designed to shut off power to prevent too much energy damaging the system – to function as designed, stopping trains. Filippi said crews then checked the subway for the cause of the surge and found an “old, worn-out” insulator that “does not appear to be related to this latest event.” But BART operators have reported other explosions recently, and the agency has found damaged insulators in some of the incidents now under investigation by a third-party expert. Experts say insulators are ceramic devices designed to keep power from flowing from the high-voltage third rail into the ground. A blown insulator was found after a fire in the Transbay Tube on Aug. 29, which filled the tunnel with smoke and stopped a train. BART has called in experts to review the cause of that incident. Smoky incidents continued in October, including one on Oct. 7th near Embarcadero station in which the operator reported witnessing an insulator explode “right in front of me.” BART has blamed that incident on unspecified debris in the trackway, not insulator failure. On Nov. 25, another train operator recounted seeing an explosion in front of his train. BART acknowledged that an insulator did explode, but suggested debris – possibly hurled by a vandal – may be to blame. While BART has discounted sudden insulator failure, alone, for any of the incidents, BART officials previously have attributed two incidents back in 2015 to dust collecting on insulators. When too much dust collects, it can allow power to flow from the third rail to the ground, creating a sudden “flash-over” event and possible fire inside a confined subway area. BART records show that BART had cleaned its insulators following the two 2015 incidents. But BART stopped cleaning them in 2020 – opting to replace old insulators instead. BART officials explained that it stopped the cleaning to avoid the risk of dry ice particles damaging the protective coating and limit their lifespan. However, BART recently told its governing board that it is reconsidering whether to restart periodic cleaning. ...read more read less