Battalion Chief Jack Piccinini said several white plastic 1-gallon containers holding muriatic acid and chlorine or sodium bicarbonate tablets fell from the back of an eastbound truck shortly before 8 a.m.
The liquid and powder mixed, forming a vapor cloud that forced the closure of the road in both directions between Mendocino Avenue and Altruria Drive, Piccinini said.
Witnesses said the truck driver stopped and took some of the busted plastic containers, and tried to clean up the mess, but appeared to be affected by the vapor cloud and drove away, Piccinini said.
His identity is still unknown, but it is believed he works for a pool-cleaning company, Piccinini said.
Firefighters found three undamaged plastic containers and one half-full container when they arrived, Piccinini said.
A woman who drove through the area reported feeling ill and was taken to Sutter Medical Center of Santa Rosa, Piccinini said.
The road closure created a traffic nightmare on nearby surface streets, Piccinini said. No businesses or residents were evacuated.
The Santa Rosa Fire Department's hazardous materials team has cleaned up the spill and expected to reopen the road in the early afternoon.