One worker went to the hospital and two were treated at the scene after they inhaled fumes, said Cork Witte, a production supervisor.
Fifteen people had to be decontaminated, officials said. The process includes changing clothes and washing, said Pam Bright, Indiana Department of Homeland Security spokeswoman.
Workers were mixing chemicals when the acid cloud was created, and the plant was evacuated in the early afternoon, Dick said.
Hydrochloric acid is highly corrosive and is often used in metal and plastics work. Exposure can irritate the eyes and skin and cause respiratory problems and dizziness. In extreme cases, death can occur.
A hazardous materials team was sent to the plant in Carefree, about 35 miles west of Louisville, Ky., Dick said.
Jasper Engines employs about 1,600 people at locations in Jasper and Crawford County. The company refurbishes engines and transmissions.