RODEO (CBS SF) – Contra Costa County hazardous materials officials said at least 10 people have reported nausea, throat irritation and respiratory symptoms due to gas released in the air from a water tank rupture Thursday at the ConocoPhillips refinery in Rodeo.

A ruptured seam on a sulfur-water tank at the plant around 7 a.m. caused a sour smell and reports of adverse health effects, but the levels of hydrogen sulfide in the air remain about 1,000 times below what is considered dangerous, said officials at the Contra Costa County Hazardous Materials Program.

Program director Randy Sawyer said the hydrogen sulfide measured as much as 65 parts per billion at Cummings Skyway and Interstate 80, “which is a very, very strong odor.”

Sawyer said ConocoPhillips was pumping out the one million-gallon tank, and was considering adding diesel which would float to the top of the tank and prevent the sulfur from leaving the water.

The Contra Costa County Health Department has advised people with respiratory problems to stay indoors or avoid Crockett, Rodeo, Hercules and other areas around the refinery.

Sawyer did not have an estimate for how long the health advisory would remain in place.

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