"Vapor leaks are very dangerous, because they can just trigger like that, explode without any forewarning," Bay Area Air Quality Management District director Mark Ross said.
And that, say investigators, is exactly what happened. Early findings in the report by the CSB reveals that a large number of workers were engulfed in the refinery's vapor cloud caused by the hydrocarbon leak. Workers that might have been killed or severely injured, had they not escaped as the cloud ignited shortly after.
Workers noticed the leak and were in the process of repairs when the leak, without warning, intensified, sparking a fire and a trail of smoke that could be seen for miles.
Before Ross was a director and former chairman of the Bay Area Air Quality Management District, he was a refinery operator with more than a decade of experience under his belt.
"There are very intense pressures in these columns that are cooking the crude, up 750 degrees, very hot, very pressurized and when you remove that bandage or that clamp over a leak, bad things can happen and apparently, that's what happened," he said.
According to the CSB, both Chevron and the United Steelworkers have been cooperating with the investigation.
Safety inspectors could be seen Monday combing through the site of the fire searching for clues and looking for the answers to tough questions, just like the crew that works there.
"We need to make sure we get a thorough root cause investigation accomplished," United Steelworkers spokesperson Jeff Clark said.
The CSB says that an unrelated inspection in November led Chevron to replace an old pipe connected to the one that failed last Monday. Now, their investigation will also probe why the pipe that failed was kept in service at all.
And, Ross says, there's more.
"You're also going to have to check pipes that apparently weren't damaged; you have to check all the valves and meters and monitors, everything around the unit to make sure it wasn't damaged by the intense heat of the fire, even though apparently it may be intact," he said.
For their part, Chevron says that CSB in onsite, continuing their investigation, as are other agencies.
CSB investigations look into all aspects of chemical accidents including physical causes and equipment failure.