MARTINEZ (KCBS) – Contra Costa County, which has the highest concentration of petro-chemical plants in Northern California, has seen a significant decline in serious chemical accidents over the last few years.

The 1990’s were a tough time in terms of severity Level 3 petro-chemical accidents in Contra Costa. In 1992 at the Rhone-Poulenc facility in Martinez, one person was killed and another seriously injured.

The following year, a sulfuric acid cloud was released from General Chemical in Richmond, with thousands seeking medical treatment. But County Hazardous Materials Director Randy Sawyer said the deadliest incident was at the Tosco Refinery in 1999.

“It was a flash fire at a crude unit. Four workers were killed and another was seriously injured,” he said.

KCBS’ Dave Padilla Reports:

But Sawyer said over the last decade, the number of petro-chemicals accidents has dropped off.

“Since 1999, we haven’t had a major accident where there’s been a fatality at a facility or a major impact to the community,” Sawyer said.

Sawyer said there were four severity Level 1 incidents last year, with two coming at the Tesoro Refinery.

He credits the county’s tough Industrial Safety Ordinance, viewed as the toughest in the country, and a dramatic shift in the safety culture at refineries for the drastic reduction in these type of accidents.

(© 2011 CBS Broadcasting Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)