The tanker was unloading anhydrous ammonia at a Tanner Industries distribution facility in Lexington County about 8 a.m. when a hose connecting the truck to a storage tank ruptured, Department of Health and Environmental Control spokesman Thom Berry said.
About 1,800 gallons of the 7,500 gallons on board spilled out before one of the truck's drivers could hit an emergency shutoff valve, Berry said.
The ammonia a hazardous chemical typically used in cleaning products quickly evaporated, creating a plume of noxious gas that drifted across nearby U.S. Highway 321, Berry said.
Jacqueline Ginyard, 38, of Wagener, drove into the cloud, tried to get out of her vehicle and was overcome by the fumes, Lexington County Coroner Harry Harman said.
"This material was nearly 100 percent pure ammonia," Berry said. "It is a strong irritant. It does cause burning of the eyes, throat and lungs."
In all, more than a dozen people in the area received medical attention. Seven were taken to a hospital in Lexington for treatment of non-life threatening injuries, while seven others either declined treatment or were assisted at the scene, Berry said.
All employees at the Tanner facility were evacuated.
Officials do not believe nearby residents are in danger, although Berry said several DHEC teams are going door-to-door in the predominantly rural area, talking with people about the leak. The agency has also set up a toll-free number for questions.
Since the ammonia evaporated almost instantly, little cleanup is needed, Berry said, although some bushes and grass were blackened by the spilled liquid.
A spokesman for Tanner Industries said the Southampton, Pa.-based company would send a team to South Carolina to investigate.
"It's been a terrible day for us obviously," said David Binder. "We've had a good track record, and we've always been committed to protecting the health and safety of employees, communities and the environment."
Binder said Tanner processes anhydrous ammonia and other chemical products used by power plants, cold-storage facilities and water-treatment plants.
The U.S. Chemical Safety Board is also sending a team of investigators.
Authorities are still looking at the role of ammonia gas released in a blast at a North Carolina ConAgra Inc. last month that killed three people. Several weeks later, an ammonia leak at a poultry processing plant in the state killed one worker and injured four others.