Authorities went door to door to warn the 2,500 people living within 3 miles to evacuate. About 250 went to shelters in nearby Karns City, North Washington and Bruin.
Authorities were concerned about the potential for respiratory damage and skin burns, said Freda Tarbell, spokeswoman for the state Department of Environmental Protection. She said residents were cleared to return home after officials from the federal Environmental Protection Agency monitored the air and determined that no acid remained.
Authorities said three residents were taken to hospitals with apparent respiratory problems, but it was unclear whether the problems were related to the leak.
Residents who were in the path of the dense cloud Saturday night were told to remain inside, to close doors, windows and vents, to shut down any system that draws air from the outside, and to put out any fires in fireplaces.
The plant, which produces a bonding agent for the tire industry, will remain closed until the cleanup is completed.