After a mysterious, sulfurous scent from god knows where had San Franciscans plugging up their noses in two December incidents, fingers were pointing at Richmond's Chevron refinery. Were two flareups there that had occurred just before the smell emerged in San Francisco really to blame? Supervisor Mark Farrell called for a hearing into whatever caused the flares, and the cause of the odor is also under investigation by the Bay Area Air Quality Management District.

Chevron submitted two reports to Contra Costa County health officials on the incidents, and KQED reports that the problems led Chevron to demand greater caution from contract workers and to consider upgrading plant alarm systems. The report is here, and you'll see why those conclusions were drawn after reading a bit more.

The first breakdown at the refinery occurred at 11:45 p.m. on December 27. That was caused by a clogged line that separated liquid and gas, but filled with too much liquid, triggering an alarm. The flare gas compressor was turned off for about an hour, and a backup flaring system at the refinery was activated.

Good to know, says Randy Sawyer, county chief environmental health and hazardous materials officer. But it would be better to know even more. “You would like to find out what caused the plug so you can prevent that from happening,” Sawyer told KQED. “It does not look like they’re investigating what actually caused the plug.”

The second flare problem, 16 hours later, lasted longer and was caused by human error according to the report. A compressor was "starved for gas" and had nothing to compress. Without high pressure, the flaring system was operated. What happened? Where was the gas that was supposed to enter the compressor? A device that's placed between two sections of pipe to close them off from each other during maintenance, with a steel plate, called a blind flange, was never removed, because it was supposed to be labelled, with a "T" tab, for turnaround, and was never labeled. The label thing, apparently, wasn't clear to a contracting company who were working on the maintenance.

The report is only partially satisfying to Sawyer, for one. Why, he says he wants to know, were unusually high amounts of hydrogen sulfide detected by one of Chevron's air monitors after at least one and maybe both of the flares? Chevron says it's not quite finished with an investigation into that aspect of the issue.

For those who'd like to dig deeper into Richmond's history with Chevron, the timing, as it so happens, is just right. Labor activist and writer Steve Early released Refinery Town, with a foreword by Bernie Sanders, to a positive review in the Chronicle. Early traces his interest to the 2012 refinery fire there, which made a strong impression on him when he moved west from New England.

Previously: Mysterious Stench Returns With A Vengeance, Chevron Facility In Richmond Suspected Culprit